SipHash is a 64-bit keyed hash function that is actually a
cryptographically secure PRF, like HMAC. Except SipHash is super fast,
and is meant to be used as a hashtable keyed lookup function.
SipHash isn't just some new trendy hash function. It's been around for a
while, and there really isn't anything that comes remotely close to
being useful in the way SipHash is. With that said, why do we need this?
There are a variety of attacks known as "hashtable poisoning" in which an
attacker forms some data such that the hash of that data will be the
same, and then preceeds to fill up all entries of a hashbucket. This is
a realistic and well-known denial-of-service vector.
Linux developers already seem to be aware that this is an issue, and
various places that use hash tables in, say, a network context, use a
non-cryptographically secure function (usually jhash) and then try to
twiddle with the key on a time basis (or in many cases just do nothing
and hope that nobody notices). While this is an admirable attempt at
solving the problem, it doesn't actually fix it. SipHash fixes it.
(It fixes it in such a sound way that you could even build a stream
cipher out of SipHash that would resist the modern cryptanalysis.)
There are a modicum of places in the kernel that are vulnerable to
hashtable poisoning attacks, either via userspace vectors or network
vectors, and there's not a reliable mechanism inside the kernel at the
moment to fix it. The first step toward fixing these issues is actually
getting a secure primitive into the kernel for developers to use. Then
we can, bit by bit, port things over to it as deemed appropriate.
Dozens of languages are already using this internally for their hash
tables. Some of the BSDs already use this in their kernels. SipHash is
a widely known high-speed solution to a widely known problem, and it's
time we catch-up.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Jean-Philippe Aumasson <[email protected]>
Cc: Daniel J. Bernstein <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Eric Biggers <[email protected]>
---
Changes from v1->v2:
- None in this patch, but see elsewhere in series.
include/linux/siphash.h | 20 +++++++++++++
lib/Kconfig.debug | 6 ++--
lib/Makefile | 5 ++--
lib/siphash.c | 76 +++++++++++++++++++++++++++++++++++++++++++++++++
lib/test_siphash.c | 74 +++++++++++++++++++++++++++++++++++++++++++++++
5 files changed, 176 insertions(+), 5 deletions(-)
create mode 100644 include/linux/siphash.h
create mode 100644 lib/siphash.c
create mode 100644 lib/test_siphash.c
diff --git a/include/linux/siphash.h b/include/linux/siphash.h
new file mode 100644
index 000000000000..6623b3090645
--- /dev/null
+++ b/include/linux/siphash.h
@@ -0,0 +1,20 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#ifndef _LINUX_SIPHASH_H
+#define _LINUX_SIPHASH_H
+
+#include <linux/types.h>
+
+enum siphash_lengths {
+ SIPHASH24_KEY_LEN = 16
+};
+
+u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN]);
+
+#endif /* _LINUX_SIPHASH_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e6327d102184..32bbf689fc46 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1843,9 +1843,9 @@ config TEST_HASH
tristate "Perform selftest on hash functions"
default n
help
- Enable this option to test the kernel's integer (<linux/hash,h>)
- and string (<linux/stringhash.h>) hash functions on boot
- (or module load).
+ Enable this option to test the kernel's integer (<linux/hash.h>),
+ string (<linux/stringhash.h>), and siphash (<linux/siphash.h>)
+ hash functions on boot (or module load).
This is intended to help people writing architecture-specific
optimized versions. If unsure, say N.
diff --git a/lib/Makefile b/lib/Makefile
index 50144a3aeebd..71d398b04a74 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -22,7 +22,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
sha1.o chacha20.o md5.o irq_regs.o argv_split.o \
flex_proportions.o ratelimit.o show_mem.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
- earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
+ earlycpio.o seq_buf.o siphash.o \
+ nmi_backtrace.o nodemask.o win_minmax.o
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
@@ -44,7 +45,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
obj-y += kstrtox.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
-obj-$(CONFIG_TEST_HASH) += test_hash.o
+obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
obj-$(CONFIG_TEST_KASAN) += test_kasan.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
obj-$(CONFIG_TEST_LKM) += test_module.o
diff --git a/lib/siphash.c b/lib/siphash.c
new file mode 100644
index 000000000000..7b55ad3a7fe9
--- /dev/null
+++ b/lib/siphash.c
@@ -0,0 +1,76 @@
+/* Copyright (C) 2015-2016 Jason A. Donenfeld <[email protected]>
+ * Copyright (C) 2012-2014 Jean-Philippe Aumasson <[email protected]>
+ * Copyright (C) 2012-2014 Daniel J. Bernstein <[email protected]>
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <asm/unaligned.h>
+
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+#include <linux/dcache.h>
+#include <asm/word-at-a-time.h>
+#endif
+
+#define SIPROUND \
+ do { \
+ v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
+ v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
+ v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
+ v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
+ } while(0)
+
+u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
+{
+ u64 v0 = 0x736f6d6570736575ULL;
+ u64 v1 = 0x646f72616e646f6dULL;
+ u64 v2 = 0x6c7967656e657261ULL;
+ u64 v3 = 0x7465646279746573ULL;
+ u64 b = ((u64)len) << 56;
+ u64 k0 = get_unaligned_le64(key);
+ u64 k1 = get_unaligned_le64(key + sizeof(u64));
+ u64 m;
+ const u8 *end = data + len - (len % sizeof(u64));
+ const u8 left = len & (sizeof(u64) - 1);
+ v3 ^= k1;
+ v2 ^= k0;
+ v1 ^= k1;
+ v0 ^= k0;
+ for (; data != end; data += sizeof(u64)) {
+ m = get_unaligned_le64(data);
+ v3 ^= m;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= m;
+ }
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+ if (left)
+ b |= le64_to_cpu(load_unaligned_zeropad(data) & bytemask_from_count(left));
+#else
+ switch (left) {
+ case 7: b |= ((u64)data[6]) << 48;
+ case 6: b |= ((u64)data[5]) << 40;
+ case 5: b |= ((u64)data[4]) << 32;
+ case 4: b |= get_unaligned_le32(data); break;
+ case 3: b |= ((u64)data[2]) << 16;
+ case 2: b |= get_unaligned_le16(data); break;
+ case 1: b |= data[0];
+ }
+#endif
+ v3 ^= b;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= b;
+ v2 ^= 0xff;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ return (v0 ^ v1) ^ (v2 ^ v3);
+}
+EXPORT_SYMBOL(siphash24);
diff --git a/lib/test_siphash.c b/lib/test_siphash.c
new file mode 100644
index 000000000000..336298aaa33b
--- /dev/null
+++ b/lib/test_siphash.c
@@ -0,0 +1,74 @@
+/* Test cases for siphash.c
+ *
+ * Copyright (C) 2015-2016 Jason A. Donenfeld <[email protected]>
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+
+/* Test vectors taken from official reference source available at:
+ * https://131002.net/siphash/siphash24.c
+ */
+static const u64 test_vectors[64] = {
+ 0x726fdb47dd0e0e31ULL, 0x74f839c593dc67fdULL, 0x0d6c8009d9a94f5aULL,
+ 0x85676696d7fb7e2dULL, 0xcf2794e0277187b7ULL, 0x18765564cd99a68dULL,
+ 0xcbc9466e58fee3ceULL, 0xab0200f58b01d137ULL, 0x93f5f5799a932462ULL,
+ 0x9e0082df0ba9e4b0ULL, 0x7a5dbbc594ddb9f3ULL, 0xf4b32f46226bada7ULL,
+ 0x751e8fbc860ee5fbULL, 0x14ea5627c0843d90ULL, 0xf723ca908e7af2eeULL,
+ 0xa129ca6149be45e5ULL, 0x3f2acc7f57c29bdbULL, 0x699ae9f52cbe4794ULL,
+ 0x4bc1b3f0968dd39cULL, 0xbb6dc91da77961bdULL, 0xbed65cf21aa2ee98ULL,
+ 0xd0f2cbb02e3b67c7ULL, 0x93536795e3a33e88ULL, 0xa80c038ccd5ccec8ULL,
+ 0xb8ad50c6f649af94ULL, 0xbce192de8a85b8eaULL, 0x17d835b85bbb15f3ULL,
+ 0x2f2e6163076bcfadULL, 0xde4daaaca71dc9a5ULL, 0xa6a2506687956571ULL,
+ 0xad87a3535c49ef28ULL, 0x32d892fad841c342ULL, 0x7127512f72f27cceULL,
+ 0xa7f32346f95978e3ULL, 0x12e0b01abb051238ULL, 0x15e034d40fa197aeULL,
+ 0x314dffbe0815a3b4ULL, 0x027990f029623981ULL, 0xcadcd4e59ef40c4dULL,
+ 0x9abfd8766a33735cULL, 0x0e3ea96b5304a7d0ULL, 0xad0c42d6fc585992ULL,
+ 0x187306c89bc215a9ULL, 0xd4a60abcf3792b95ULL, 0xf935451de4f21df2ULL,
+ 0xa9538f0419755787ULL, 0xdb9acddff56ca510ULL, 0xd06c98cd5c0975ebULL,
+ 0xe612a3cb9ecba951ULL, 0xc766e62cfcadaf96ULL, 0xee64435a9752fe72ULL,
+ 0xa192d576b245165aULL, 0x0a8787bf8ecb74b2ULL, 0x81b3e73d20b49b6fULL,
+ 0x7fa8220ba3b2eceaULL, 0x245731c13ca42499ULL, 0xb78dbfaf3a8d83bdULL,
+ 0xea1ad565322a1a0bULL, 0x60e61c23a3795013ULL, 0x6606d7e446282b93ULL,
+ 0x6ca4ecb15c5f91e1ULL, 0x9f626da15c9625f3ULL, 0xe51b38608ef25f57ULL,
+ 0x958a324ceb064572ULL
+};
+
+static int __init siphash_test_init(void)
+{
+ u8 in[64], k[16], i;
+ int ret = 0;
+
+ for (i = 0; i < 16; ++i)
+ k[i] = i;
+ for (i = 0; i < 64; ++i) {
+ in[i] = i;
+ if (siphash24(in, i, k) != test_vectors[i]) {
+ pr_info("self-test %u: FAIL\n", i + 1);
+ ret = -EINVAL;
+ }
+ }
+ if (!ret)
+ pr_info("self-tests: pass\n");
+ return ret;
+}
+
+static void __exit siphash_test_exit(void)
+{
+}
+
+module_init(siphash_test_init);
+module_exit(siphash_test_exit);
+
+MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");
+MODULE_LICENSE("Dual BSD/GPL");
--
2.11.0
Many jhash users currently rely on the Nwords functions. In order to
make transitions to siphash fit something people already know about, we
provide analog functions here. This also winds up being nice for the
networking stack, where hashing 32-bit fields is common.
Signed-off-by: Jason A. Donenfeld <[email protected]>
---
Changes from v1->v2:
- None in this patch, but see elsewhere in series.
include/linux/siphash.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)
diff --git a/include/linux/siphash.h b/include/linux/siphash.h
index 6623b3090645..1391054c4c29 100644
--- a/include/linux/siphash.h
+++ b/include/linux/siphash.h
@@ -17,4 +17,37 @@ enum siphash_lengths {
u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN]);
+static inline u64 siphash24_1word(const u32 a, const u8 key[SIPHASH24_KEY_LEN])
+{
+ return siphash24((u8 *)&a, sizeof(a), key);
+}
+
+static inline u64 siphash24_2words(const u32 a, const u32 b, const u8 key[SIPHASH24_KEY_LEN])
+{
+ const struct {
+ u32 a;
+ u32 b;
+ } __packed combined = {
+ .a = a,
+ .b = b
+ };
+
+ return siphash24((const u8 *)&combined, sizeof(combined), key);
+}
+
+static inline u64 siphash24_3words(const u32 a, const u32 b, const u32 c, const u8 key[SIPHASH24_KEY_LEN])
+{
+ const struct {
+ u32 a;
+ u32 b;
+ u32 c;
+ } __packed combined = {
+ .a = a,
+ .b = b,
+ .c = c
+ };
+
+ return siphash24((const u8 *)&combined, sizeof(combined), key);
+}
+
#endif /* _LINUX_SIPHASH_H */
--
2.11.0
This gives a clear speed and security improvement. Siphash is both
faster and is more solid crypto than the aging MD5.
Rather than manually filling MD5 buffers, we simply create
a layout by a simple anonymous struct, for which gcc generates
rather efficient code.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Andi Kleen <[email protected]>
---
Changes from v1->v2:
- Rebased on the latest 4.10, and now uses top 32-bits of siphash
for the optional ts value.
net/core/secure_seq.c | 160 +++++++++++++++++++++++++-------------------------
1 file changed, 79 insertions(+), 81 deletions(-)
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 88a8e429fc3e..abadc79cd5d3 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -1,3 +1,5 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>. All Rights Reserved. */
+
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/cryptohash.h>
@@ -8,14 +10,14 @@
#include <linux/ktime.h>
#include <linux/string.h>
#include <linux/net.h>
-
+#include <linux/siphash.h>
#include <net/secure_seq.h>
#if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
+#include <linux/in6.h>
#include <net/tcp.h>
-#define NET_SECRET_SIZE (MD5_MESSAGE_BYTES / 4)
-static u32 net_secret[NET_SECRET_SIZE] ____cacheline_aligned;
+static u8 net_secret[SIPHASH24_KEY_LEN];
static __always_inline void net_secret_init(void)
{
@@ -44,44 +46,39 @@ static u32 seq_scale(u32 seq)
u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
__be16 sport, __be16 dport, u32 *tsoff)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
- u32 i;
-
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 sport;
+ __be16 dport;
+ } __packed combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .sport = sport,
+ .dport = dport
+ };
+ u64 hash;
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32)daddr[i];
- secret[4] = net_secret[4] +
- (((__force u16)sport << 16) + (__force u16)dport);
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- *tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
- return seq_scale(hash[0]);
+ hash = siphash24((const u8 *)&combined, sizeof(combined), net_secret);
+ *tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;
+ return seq_scale(hash);
}
EXPORT_SYMBOL(secure_tcpv6_sequence_number);
u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
__be16 dport)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
- u32 i;
-
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 dport;
+ } __packed combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .dport = dport
+ };
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32) daddr[i];
- secret[4] = net_secret[4] + (__force u32)dport;
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- return hash[0];
+ return siphash24((const u8 *)&combined, sizeof(combined), net_secret);
}
EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
#endif
@@ -91,33 +88,37 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport, u32 *tsoff)
{
- u32 hash[MD5_DIGEST_WORDS];
-
+ const struct {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 sport;
+ __be16 dport;
+ } __packed combined = {
+ .saddr = saddr,
+ .daddr = daddr,
+ .sport = sport,
+ .dport = dport
+ };
+ u64 hash;
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- *tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
- return seq_scale(hash[0]);
+ hash = siphash24((const u8 *)&combined, sizeof(combined), net_secret);
+ *tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;
+ return seq_scale(hash);
}
u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
- u32 hash[MD5_DIGEST_WORDS];
-
+ const struct {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 dport;
+ } __packed combined = {
+ .saddr = saddr,
+ .daddr = daddr,
+ .dport = dport
+ };
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = (__force u32)dport ^ net_secret[14];
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- return hash[0];
+ return seq_scale(siphash24((const u8 *)&combined, sizeof(combined), net_secret));
}
EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
#endif
@@ -126,21 +127,22 @@ EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport)
{
- u32 hash[MD5_DIGEST_WORDS];
+ const struct {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 sport;
+ __be16 dport;
+ } __packed combined = {
+ .saddr = saddr,
+ .daddr = daddr,
+ .sport = sport,
+ .dport = dport
+ };
u64 seq;
-
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- seq = hash[0] | (((u64)hash[1]) << 32);
+ seq = siphash24((const u8 *)&combined, sizeof(combined), net_secret);
seq += ktime_get_real_ns();
seq &= (1ull << 48) - 1;
-
return seq;
}
EXPORT_SYMBOL(secure_dccp_sequence_number);
@@ -149,26 +151,22 @@ EXPORT_SYMBOL(secure_dccp_sequence_number);
u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
__be16 sport, __be16 dport)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 sport;
+ __be16 dport;
+ } __packed combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .sport = sport,
+ .dport = dport
+ };
u64 seq;
- u32 i;
-
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32)daddr[i];
- secret[4] = net_secret[4] +
- (((__force u16)sport << 16) + (__force u16)dport);
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- seq = hash[0] | (((u64)hash[1]) << 32);
+ seq = siphash24((const u8 *)&combined, sizeof(combined), net_secret);
seq += ktime_get_real_ns();
seq &= (1ull << 48) - 1;
-
return seq;
}
EXPORT_SYMBOL(secure_dccpv6_sequence_number);
--
2.11.0
This duplicates the current algorithm for get_random_int/long, but uses
siphash24 instead. This comes with several benefits. It's certainly
faster and more cryptographically secure than MD5. This patch also
hashes the pid, entropy, and timestamp as fixed width fields, in order
to increase diffusion.
The previous md5 algorithm used a per-cpu md5 state, which caused
successive calls to the function to chain upon each other. While it's
not entirely clear that this kind of chaining is absolutely necessary
when using a secure PRF like siphash24, it can't hurt, and the timing of
the call chain does add a degree of natural entropy. So, in keeping with
this design, instead of the massive per-cpu 64-byte md5 state, there is
instead a per-cpu previously returned value for chaining.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Jean-Philippe Aumasson <[email protected]>
Cc: Ted Tso <[email protected]>
---
Changes from v1->v2:
- Uses u64 instead of uint64_t
- Uses get_cpu_ptr instead of get_cpu_var
drivers/char/random.c | 50 +++++++++++++++++++++++++++++++-------------------
1 file changed, 31 insertions(+), 19 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index d6876d506220..61c4b45427dc 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -262,6 +262,7 @@
#include <linux/syscalls.h>
#include <linux/completion.h>
#include <linux/uuid.h>
+#include <linux/siphash.h>
#include <crypto/chacha20.h>
#include <asm/processor.h>
@@ -2042,7 +2043,7 @@ struct ctl_table random_table[] = {
};
#endif /* CONFIG_SYSCTL */
-static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
+static u8 random_int_secret[SIPHASH24_KEY_LEN];
int random_int_secret_init(void)
{
@@ -2050,8 +2051,7 @@ int random_int_secret_init(void)
return 0;
}
-static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash)
- __aligned(sizeof(unsigned long));
+static DEFINE_PER_CPU(u64, get_random_int_chaining);
/*
* Get a random word for internal kernel use only. Similar to urandom but
@@ -2061,19 +2061,25 @@ static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash)
*/
unsigned int get_random_int(void)
{
- __u32 *hash;
unsigned int ret;
+ struct {
+ u64 chaining;
+ unsigned long ts;
+ unsigned long entropy;
+ pid_t pid;
+ } __packed combined;
+ u64 *chaining;
if (arch_get_random_int(&ret))
return ret;
- hash = get_cpu_var(get_random_int_hash);
-
- hash[0] += current->pid + jiffies + random_get_entropy();
- md5_transform(hash, random_int_secret);
- ret = hash[0];
- put_cpu_var(get_random_int_hash);
-
+ chaining = get_cpu_ptr(&get_random_int_chaining);
+ combined.chaining = *chaining;
+ combined.ts = jiffies;
+ combined.entropy = random_get_entropy();
+ combined.pid = current->pid;
+ ret = *chaining = siphash24((u8 *)&combined, sizeof(combined), random_int_secret);
+ put_cpu_ptr(chaining);
return ret;
}
EXPORT_SYMBOL(get_random_int);
@@ -2083,19 +2089,25 @@ EXPORT_SYMBOL(get_random_int);
*/
unsigned long get_random_long(void)
{
- __u32 *hash;
unsigned long ret;
+ struct {
+ u64 chaining;
+ unsigned long ts;
+ unsigned long entropy;
+ pid_t pid;
+ } __packed combined;
+ u64 *chaining;
if (arch_get_random_long(&ret))
return ret;
- hash = get_cpu_var(get_random_int_hash);
-
- hash[0] += current->pid + jiffies + random_get_entropy();
- md5_transform(hash, random_int_secret);
- ret = *(unsigned long *)hash;
- put_cpu_var(get_random_int_hash);
-
+ chaining = get_cpu_ptr(&get_random_int_chaining);
+ combined.chaining = *chaining;
+ combined.ts = jiffies;
+ combined.entropy = random_get_entropy();
+ combined.pid = current->pid;
+ ret = *chaining = siphash24((u8 *)&combined, sizeof(combined), random_int_secret);
+ put_cpu_ptr(chaining);
return ret;
}
EXPORT_SYMBOL(get_random_long);
--
2.11.0
Hello,
On 14.12.2016 04:59, Jason A. Donenfeld wrote:
> SipHash is a 64-bit keyed hash function that is actually a
> cryptographically secure PRF, like HMAC. Except SipHash is super fast,
> and is meant to be used as a hashtable keyed lookup function.
Can you show or cite benchmarks in comparison with jhash? Last time I
looked, especially for short inputs, siphash didn't beat jhash (also on
all the 32 bit devices etc.).
> SipHash isn't just some new trendy hash function. It's been around for a
> while, and there really isn't anything that comes remotely close to
> being useful in the way SipHash is. With that said, why do we need this?
>
> There are a variety of attacks known as "hashtable poisoning" in which an
> attacker forms some data such that the hash of that data will be the
> same, and then preceeds to fill up all entries of a hashbucket. This is
> a realistic and well-known denial-of-service vector.
This pretty much depends on the linearity of the hash function? I don't
think a crypto secure hash function is needed for a hash table. Albeit I
agree that siphash certainly looks good to be used here.
> Linux developers already seem to be aware that this is an issue, and
> various places that use hash tables in, say, a network context, use a
> non-cryptographically secure function (usually jhash) and then try to
> twiddle with the key on a time basis (or in many cases just do nothing
> and hope that nobody notices). While this is an admirable attempt at
> solving the problem, it doesn't actually fix it. SipHash fixes it.
I am pretty sure that SipHash still needs a random key per hash table
also. So far it was only the choice of hash function you are questioning.
> (It fixes it in such a sound way that you could even build a stream
> cipher out of SipHash that would resist the modern cryptanalysis.)
>
> There are a modicum of places in the kernel that are vulnerable to
> hashtable poisoning attacks, either via userspace vectors or network
> vectors, and there's not a reliable mechanism inside the kernel at the
> moment to fix it. The first step toward fixing these issues is actually
> getting a secure primitive into the kernel for developers to use. Then
> we can, bit by bit, port things over to it as deemed appropriate.
Hmm, I tried to follow up with all the HashDoS work and so far didn't
see any HashDoS attacks against the Jenkins/SpookyHash family.
If this is an issue we might need to also put those changes into stable.
> Dozens of languages are already using this internally for their hash
> tables. Some of the BSDs already use this in their kernels. SipHash is
> a widely known high-speed solution to a widely known problem, and it's
> time we catch-up.
Bye,
Hannes
Hi David,
On Wed, Dec 14, 2016 at 10:56 AM, David Laight <[email protected]> wrote:
> ...
>> +u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
> ...
>> + u64 k0 = get_unaligned_le64(key);
>> + u64 k1 = get_unaligned_le64(key + sizeof(u64));
> ...
>> + m = get_unaligned_le64(data);
>
> All these unaligned accesses are going to get expensive on architectures
> like sparc64.
Yes, the unaligned accesses aren't pretty. Since in pretty much all
use cases thus far, the data can easily be made aligned, perhaps it
makes sense to create siphash24() and siphash24_unaligned(). Any
thoughts on doing something like that?
Jason
Hi David,
On Wed, Dec 14, 2016 at 10:51 AM, David Laight <[email protected]> wrote:
> From: Jason A. Donenfeld
>> Sent: 14 December 2016 00:17
>> This gives a clear speed and security improvement. Rather than manually
>> filling MD5 buffers, we simply create a layout by a simple anonymous
>> struct, for which gcc generates rather efficient code.
> ...
>> + const struct {
>> + struct in6_addr saddr;
>> + struct in6_addr daddr;
>> + __be16 sport;
>> + __be16 dport;
>> + } __packed combined = {
>> + .saddr = *(struct in6_addr *)saddr,
>> + .daddr = *(struct in6_addr *)daddr,
>> + .sport = sport,
>> + .dport = dport
>> + };
>
> You need to look at the effect of marking this (and the other)
> structures 'packed' on architectures like sparc64.
In all current uses of __packed in the code, I think the impact is
precisely zero, because all structures have members in descending
order of size, with each member being a perfect multiple of the one
below it. The __packed is therefore just there for safety, in case
somebody comes in and screws everything up by sticking a u8 in
between. In that case, it wouldn't be desirable to hash the structure
padding bits. In the worst case, I don't believe the impact would be
worse than a byte-by-byte memcpy, which is what the old code did. But
anyway, these structures are already naturally packed anyway, so the
present impact is nil.
Jason
Hi Hannes,
On Wed, Dec 14, 2016 at 12:21 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> Can you show or cite benchmarks in comparison with jhash? Last time I
> looked, especially for short inputs, siphash didn't beat jhash (also on
> all the 32 bit devices etc.).
I assume that jhash is likely faster than siphash, but I wouldn't be
surprised if with optimization we can make siphash at least pretty
close on 64-bit platforms. (I'll do some tests though; maybe I'm wrong
and jhash is already slower.)
With that said, siphash is here to replace uses of jhash where
hashtable poisoning vulnerabilities make it necessary. Where there's
no significant security improvement, if there's no speed improvement
either, then of course nothing's going to change.
I should have mentioned md5_transform in this first message too, as
two other patches in this series actually replace md5_transform usage
with siphash. I think in this case, siphash is a clear performance
winner (and security winner) over md5_transform. So if the push back
against replacing jhash usages is just too high, at the very least it
remains useful already for the md5_transform usage.
> This pretty much depends on the linearity of the hash function? I don't
> think a crypto secure hash function is needed for a hash table. Albeit I
> agree that siphash certainly looks good to be used here.
In order to prevent the aforementioned poisoning attacks, a PRF with
perfect linearity is required, which is what's achieved when it's a
cryptographically secure one. Check out section 7 of
https://131002.net/siphash/siphash.pdf .
> I am pretty sure that SipHash still needs a random key per hash table
> also. So far it was only the choice of hash function you are questioning.
Siphash needs a random secret key, yes. The point is that the hash
function remains secure so long as the secret key is kept secret.
Other functions can't make the same guarantee, and so nervous periodic
key rotation is necessary, but in most cases nothing is done, and so
things just leak over time.
> Hmm, I tried to follow up with all the HashDoS work and so far didn't
> see any HashDoS attacks against the Jenkins/SpookyHash family.
>
> If this is an issue we might need to also put those changes into stable.
jhash just isn't secure; it's not a cryptographically secure PRF. If
there hasn't already been an academic paper put out there about it
this year, let's make this thread 1000 messages long to garner
attention, and next year perhaps we'll see one. No doubt that
motivated government organizations, defense contractors, criminals,
and other netizens have already done research in private. Replacing
insecure functions with secure functions is usually a good thing.
Jason
On 14.12.2016 13:53, Jason A. Donenfeld wrote:
> Hi David,
>
> On Wed, Dec 14, 2016 at 10:51 AM, David Laight <[email protected]> wrote:
>> From: Jason A. Donenfeld
>>> Sent: 14 December 2016 00:17
>>> This gives a clear speed and security improvement. Rather than manually
>>> filling MD5 buffers, we simply create a layout by a simple anonymous
>>> struct, for which gcc generates rather efficient code.
>> ...
>>> + const struct {
>>> + struct in6_addr saddr;
>>> + struct in6_addr daddr;
>>> + __be16 sport;
>>> + __be16 dport;
>>> + } __packed combined = {
>>> + .saddr = *(struct in6_addr *)saddr,
>>> + .daddr = *(struct in6_addr *)daddr,
>>> + .sport = sport,
>>> + .dport = dport
>>> + };
>>
>> You need to look at the effect of marking this (and the other)
>> structures 'packed' on architectures like sparc64.
>
> In all current uses of __packed in the code, I think the impact is
> precisely zero, because all structures have members in descending
> order of size, with each member being a perfect multiple of the one
> below it. The __packed is therefore just there for safety, in case
> somebody comes in and screws everything up by sticking a u8 in
> between. In that case, it wouldn't be desirable to hash the structure
> padding bits. In the worst case, I don't believe the impact would be
> worse than a byte-by-byte memcpy, which is what the old code did. But
> anyway, these structures are already naturally packed anyway, so the
> present impact is nil.
__packed not only removes all padding of the struct but also changes the
alignment assumptions for the whole struct itself. The rule, the struct
is aligned by its maximum alignment of a member is no longer true. That
said, the code accessing this struct will change (not on archs that can
deal efficiently with unaligned access, but on others).
A proper test for not introducing padding is to use something with
BUILD_BUG_ON. Also gcc also clears the padding of the struct, so padding
shouldn't be that bad in there (it is better than byte access on mips).
Btw. I think gcc7 gets support for store merging optimization.
Bye,
Hannes
Hi Hannes,
Thanks for the feedback.
> __packed not only removes all padding of the struct but also changes the
> alignment assumptions for the whole struct itself. The rule, the struct
> is aligned by its maximum alignment of a member is no longer true. That
> said, the code accessing this struct will change (not on archs that can
> deal efficiently with unaligned access, but on others).
That's interesting. There currently aren't any alignment requirements
in siphash because we use the unaligned helper functions, but as David
pointed out in another thread, maybe that too should change. In that
case, we'd have an aligned-only version of the function that requires
8-byte aligned input. Perhaps the best way to go about that would be
to just mark the struct as __packed __aligned(8). Or, I guess, since
64-bit accesses gets split into two on 32-bit, that'd be best descried
as __packed __aligned(sizeof(long)). Would that be an acceptable
solution?
Jason
From: Jason A. Donenfeld
> Sent: 14 December 2016 13:44
> To: Hannes Frederic Sowa
> > __packed not only removes all padding of the struct but also changes the
> > alignment assumptions for the whole struct itself. The rule, the struct
> > is aligned by its maximum alignment of a member is no longer true. That
> > said, the code accessing this struct will change (not on archs that can
> > deal efficiently with unaligned access, but on others).
>
> That's interesting. There currently aren't any alignment requirements
> in siphash because we use the unaligned helper functions, but as David
> pointed out in another thread, maybe that too should change. In that
> case, we'd have an aligned-only version of the function that requires
> 8-byte aligned input. Perhaps the best way to go about that would be
> to just mark the struct as __packed __aligned(8). Or, I guess, since
> 64-bit accesses gets split into two on 32-bit, that'd be best descried
> as __packed __aligned(sizeof(long)). Would that be an acceptable
> solution?
Just remove the __packed and ensure that the structure is 'nice'.
This includes ensuring there is no 'tail padding'.
In some cases you'll need to put the port number into a 32bit field.
I'd also require that the key be aligned.
It probably ought to be a named structure type with two 64bit members
(or with an array member that has two elements).
David
Hello,
On 14.12.2016 14:10, Jason A. Donenfeld wrote:
> On Wed, Dec 14, 2016 at 12:21 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
>> Can you show or cite benchmarks in comparison with jhash? Last time I
>> looked, especially for short inputs, siphash didn't beat jhash (also on
>> all the 32 bit devices etc.).
>
> I assume that jhash is likely faster than siphash, but I wouldn't be
> surprised if with optimization we can make siphash at least pretty
> close on 64-bit platforms. (I'll do some tests though; maybe I'm wrong
> and jhash is already slower.)
Yes, numbers would be very usable here. I am mostly concerned about
small plastic router cases. E.g. assume you double packet processing
time with a change of the hashing function at what point is the actual
packet processing more of an attack vector than the hashtable?
> With that said, siphash is here to replace uses of jhash where
> hashtable poisoning vulnerabilities make it necessary. Where there's
> no significant security improvement, if there's no speed improvement
> either, then of course nothing's going to change.
It still changes currently well working source. ;-)
> I should have mentioned md5_transform in this first message too, as
> two other patches in this series actually replace md5_transform usage
> with siphash. I think in this case, siphash is a clear performance
> winner (and security winner) over md5_transform. So if the push back
> against replacing jhash usages is just too high, at the very least it
> remains useful already for the md5_transform usage.
MD5 is considered broken because its collision resistance is broken?
SipHash doesn't even claim to have collision resistance (which we don't
need here)?
But I agree, certainly it could be a nice speed-up!
>> This pretty much depends on the linearity of the hash function? I don't
>> think a crypto secure hash function is needed for a hash table. Albeit I
>> agree that siphash certainly looks good to be used here.
>
> In order to prevent the aforementioned poisoning attacks, a PRF with
> perfect linearity is required, which is what's achieved when it's a
> cryptographically secure one. Check out section 7 of
> https://131002.net/siphash/siphash.pdf .
I think you mean non-linearity. Otherwise I agree that siphash is
certainly a better suited hashing algorithm as far as I know. But it
would be really interesting to compare some performance numbers. Hard to
say anything without them.
>> I am pretty sure that SipHash still needs a random key per hash table
>> also. So far it was only the choice of hash function you are questioning.
>
> Siphash needs a random secret key, yes. The point is that the hash
> function remains secure so long as the secret key is kept secret.
> Other functions can't make the same guarantee, and so nervous periodic
> key rotation is necessary, but in most cases nothing is done, and so
> things just leak over time.
>
>
>> Hmm, I tried to follow up with all the HashDoS work and so far didn't
>> see any HashDoS attacks against the Jenkins/SpookyHash family.
>>
>> If this is an issue we might need to also put those changes into stable.
>
> jhash just isn't secure; it's not a cryptographically secure PRF. If
> there hasn't already been an academic paper put out there about it
> this year, let's make this thread 1000 messages long to garner
> attention, and next year perhaps we'll see one. No doubt that
> motivated government organizations, defense contractors, criminals,
> and other netizens have already done research in private. Replacing
> insecure functions with secure functions is usually a good thing.
I think this is a weak argument.
In general I am in favor to switch to siphash, but it would be nice to
see some benchmarks with the specific kernel implementation also on some
smaller 32 bit CPUs and especially without using any SIMD instructions
(which might have been used in paper comparison).
Bye,
Hannes
On Wed, Dec 14, 2016 at 3:47 PM, David Laight <[email protected]> wrote:
> Just remove the __packed and ensure that the structure is 'nice'.
> This includes ensuring there is no 'tail padding'.
> In some cases you'll need to put the port number into a 32bit field.
I'd rather not. There's no point in wasting extra cycles on hashing
useless data, just for some particular syntactic improvement. __packed
__aligned(8) will do what we want perfectly, I think.
> I'd also require that the key be aligned.
Yep, I'll certainly do this for the siphash24_aligned version in the v3.
From: "Jason A. Donenfeld" <[email protected]>
Date: Wed, 14 Dec 2016 13:53:10 +0100
> In all current uses of __packed in the code, I think the impact is
> precisely zero, because all structures have members in descending
> order of size, with each member being a perfect multiple of the one
> below it. The __packed is therefore just there for safety, in case
> somebody comes in and screws everything up by sticking a u8 in
> between.
Just marking the structure __packed, whether necessary or not, makes
the compiler assume that the members are not aligned and causes
byte-by-byte accesses to be performed for words.
Never, _ever_, use __packed unless absolutely necessary, it pessimizes
the code on cpus that require proper alignment of types.
Hi David,
On Wed, Dec 14, 2016 at 6:56 PM, David Miller <[email protected]> wrote:
> Just marking the structure __packed, whether necessary or not, makes
> the compiler assume that the members are not aligned and causes
> byte-by-byte accesses to be performed for words.
> Never, _ever_, use __packed unless absolutely necessary, it pessimizes
> the code on cpus that require proper alignment of types.
Oh, jimminy cricket, I did not realize that it made assignments
byte-by-byte *always*. So what options am I left with? What
immediately comes to mind are:
1)
struct {
u64 a;
u32 b;
u32 c;
u16 d;
u8 end[];
} a = {
.a = a,
.b = b,
.c = c,
.d = d
};
siphash24(&a, offsetof(typeof(a), end), key);
2)
u8 bytes[sizeof(u64) + sizeof(u32) * 2 + sizeof(u16)];
*(u64 *)&bytes[0] = a;
*(u32 *)&bytes[sizeof(u64)] = b;
*(u32 *)&bytes[sizeof(u64) + sizeof(u32)] = c;
*(u16 *)&bytes[sizeof(u64) + sizeof(u32) * 2] = d;
siphash24(bytes, sizeof(bytes), key);
Personally I find (1) a bit neater than (2). What's your opinion?
Jason
SipHash is a 64-bit keyed hash function that is actually a
cryptographically secure PRF, like HMAC. Except SipHash is super fast,
and is meant to be used as a hashtable keyed lookup function.
SipHash isn't just some new trendy hash function. It's been around for a
while, and there really isn't anything that comes remotely close to
being useful in the way SipHash is. With that said, why do we need this?
There are a variety of attacks known as "hashtable poisoning" in which an
attacker forms some data such that the hash of that data will be the
same, and then preceeds to fill up all entries of a hashbucket. This is
a realistic and well-known denial-of-service vector.
Linux developers already seem to be aware that this is an issue, and
various places that use hash tables in, say, a network context, use a
non-cryptographically secure function (usually jhash) and then try to
twiddle with the key on a time basis (or in many cases just do nothing
and hope that nobody notices). While this is an admirable attempt at
solving the problem, it doesn't actually fix it. SipHash fixes it.
(It fixes it in such a sound way that you could even build a stream
cipher out of SipHash that would resist the modern cryptanalysis.)
There are a modicum of places in the kernel that are vulnerable to
hashtable poisoning attacks, either via userspace vectors or network
vectors, and there's not a reliable mechanism inside the kernel at the
moment to fix it. The first step toward fixing these issues is actually
getting a secure primitive into the kernel for developers to use. Then
we can, bit by bit, port things over to it as deemed appropriate.
Secondly, a few places are using MD5 for creating secure sequence
numbers, port numbers, or fast random numbers. Siphash is a faster, more
fittting, and more secure replacement for MD5 in those situations.
Dozens of languages are already using this internally for their hash
tables. Some of the BSDs already use this in their kernels. SipHash is
a widely known high-speed solution to a widely known problem, and it's
time we catch-up.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Jean-Philippe Aumasson <[email protected]>
Cc: Daniel J. Bernstein <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: David Laight <[email protected]>
---
Changes from v2->v3:
- There is now a fast aligned version of the function and a not-as-fast
unaligned version. The requirements for each have been documented in
a docbook-style comment. As well, the header now contains a constant
for the expected alignment.
- The test suite has been updated to check both the unaligned and aligned
version of the function.
include/linux/siphash.h | 30 ++++++++++
lib/Kconfig.debug | 6 +-
lib/Makefile | 5 +-
lib/siphash.c | 153 ++++++++++++++++++++++++++++++++++++++++++++++++
lib/test_siphash.c | 85 +++++++++++++++++++++++++++
5 files changed, 274 insertions(+), 5 deletions(-)
create mode 100644 include/linux/siphash.h
create mode 100644 lib/siphash.c
create mode 100644 lib/test_siphash.c
diff --git a/include/linux/siphash.h b/include/linux/siphash.h
new file mode 100644
index 000000000000..82dc1a911a2e
--- /dev/null
+++ b/include/linux/siphash.h
@@ -0,0 +1,30 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#ifndef _LINUX_SIPHASH_H
+#define _LINUX_SIPHASH_H
+
+#include <linux/types.h>
+
+enum siphash_lengths {
+ SIPHASH24_KEY_LEN = 16,
+ SIPHASH24_ALIGNMENT = 8
+};
+
+u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN]);
+
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+static inline u64 siphash24_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
+{
+ return siphash24(data, len, key);
+}
+#else
+u64 siphash24_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN]);
+#endif
+
+#endif /* _LINUX_SIPHASH_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e6327d102184..32bbf689fc46 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1843,9 +1843,9 @@ config TEST_HASH
tristate "Perform selftest on hash functions"
default n
help
- Enable this option to test the kernel's integer (<linux/hash,h>)
- and string (<linux/stringhash.h>) hash functions on boot
- (or module load).
+ Enable this option to test the kernel's integer (<linux/hash.h>),
+ string (<linux/stringhash.h>), and siphash (<linux/siphash.h>)
+ hash functions on boot (or module load).
This is intended to help people writing architecture-specific
optimized versions. If unsure, say N.
diff --git a/lib/Makefile b/lib/Makefile
index 50144a3aeebd..71d398b04a74 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -22,7 +22,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
sha1.o chacha20.o md5.o irq_regs.o argv_split.o \
flex_proportions.o ratelimit.o show_mem.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
- earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
+ earlycpio.o seq_buf.o siphash.o \
+ nmi_backtrace.o nodemask.o win_minmax.o
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
@@ -44,7 +45,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
obj-y += kstrtox.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
-obj-$(CONFIG_TEST_HASH) += test_hash.o
+obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
obj-$(CONFIG_TEST_KASAN) += test_kasan.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
obj-$(CONFIG_TEST_LKM) += test_module.o
diff --git a/lib/siphash.c b/lib/siphash.c
new file mode 100644
index 000000000000..32acdc26234f
--- /dev/null
+++ b/lib/siphash.c
@@ -0,0 +1,153 @@
+/* Copyright (C) 2015-2016 Jason A. Donenfeld <[email protected]>
+ * Copyright (C) 2012-2014 Jean-Philippe Aumasson <[email protected]>
+ * Copyright (C) 2012-2014 Daniel J. Bernstein <[email protected]>
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <asm/unaligned.h>
+
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+#include <linux/dcache.h>
+#include <asm/word-at-a-time.h>
+#endif
+
+#define SIPROUND \
+ do { \
+ v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
+ v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
+ v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
+ v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
+ } while(0)
+
+static inline u16 le16_to_cpuvp(const void *p)
+{
+ return le16_to_cpup(p);
+}
+static inline u32 le32_to_cpuvp(const void *p)
+{
+ return le32_to_cpup(p);
+}
+static inline u64 le64_to_cpuvp(const void *p)
+{
+ return le64_to_cpup(p);
+}
+
+/**
+ * siphash24 - compute 64-bit siphash24 PRF value
+ * @data: buffer to hash, must be aligned to SIPHASH24_ALIGNMENT
+ * @size: size of @data
+ * @key: key buffer of size SIPHASH24_KEY_LEN, must be aligned to SIPHASH24_ALIGNMENT
+ */
+u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
+{
+ u64 v0 = 0x736f6d6570736575ULL;
+ u64 v1 = 0x646f72616e646f6dULL;
+ u64 v2 = 0x6c7967656e657261ULL;
+ u64 v3 = 0x7465646279746573ULL;
+ u64 b = ((u64)len) << 56;
+ u64 k0 = le64_to_cpuvp(key);
+ u64 k1 = le64_to_cpuvp(key + sizeof(u64));
+ u64 m;
+ const u8 *end = data + len - (len % sizeof(u64));
+ const u8 left = len & (sizeof(u64) - 1);
+ v3 ^= k1;
+ v2 ^= k0;
+ v1 ^= k1;
+ v0 ^= k0;
+ for (; data != end; data += sizeof(u64)) {
+ m = le64_to_cpuvp(data);
+ v3 ^= m;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= m;
+ }
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+ if (left)
+ b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
+#else
+ switch (left) {
+ case 7: b |= ((u64)data[6]) << 48;
+ case 6: b |= ((u64)data[5]) << 40;
+ case 5: b |= ((u64)data[4]) << 32;
+ case 4: b |= le32_to_cpuvp(data); break;
+ case 3: b |= ((u64)data[2]) << 16;
+ case 2: b |= le16_to_cpuvp(data); break;
+ case 1: b |= data[0];
+ }
+#endif
+ v3 ^= b;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= b;
+ v2 ^= 0xff;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ return (v0 ^ v1) ^ (v2 ^ v3);
+}
+EXPORT_SYMBOL(siphash24);
+
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+/**
+ * siphash24 - compute 64-bit siphash24 PRF value, without alignment requirements
+ * @data: buffer to hash
+ * @size: size of @data
+ * @key: key buffer of size SIPHASH24_KEY_LEN
+ */
+u64 siphash24_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
+{
+ u64 v0 = 0x736f6d6570736575ULL;
+ u64 v1 = 0x646f72616e646f6dULL;
+ u64 v2 = 0x6c7967656e657261ULL;
+ u64 v3 = 0x7465646279746573ULL;
+ u64 b = ((u64)len) << 56;
+ u64 k0 = get_unaligned_le64(key);
+ u64 k1 = get_unaligned_le64(key + sizeof(u64));
+ u64 m;
+ const u8 *end = data + len - (len % sizeof(u64));
+ const u8 left = len & (sizeof(u64) - 1);
+ v3 ^= k1;
+ v2 ^= k0;
+ v1 ^= k1;
+ v0 ^= k0;
+ for (; data != end; data += sizeof(u64)) {
+ m = get_unaligned_le64(data);
+ v3 ^= m;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= m;
+ }
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+ if (left)
+ b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
+#else
+ switch (left) {
+ case 7: b |= ((u64)data[6]) << 48;
+ case 6: b |= ((u64)data[5]) << 40;
+ case 5: b |= ((u64)data[4]) << 32;
+ case 4: b |= get_unaligned_le32(data); break;
+ case 3: b |= ((u64)data[2]) << 16;
+ case 2: b |= get_unaligned_le16(data); break;
+ case 1: b |= data[0];
+ }
+#endif
+ v3 ^= b;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= b;
+ v2 ^= 0xff;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ return (v0 ^ v1) ^ (v2 ^ v3);
+}
+EXPORT_SYMBOL(siphash24_unaligned);
+#endif
diff --git a/lib/test_siphash.c b/lib/test_siphash.c
new file mode 100644
index 000000000000..69ac94dec366
--- /dev/null
+++ b/lib/test_siphash.c
@@ -0,0 +1,85 @@
+/* Test cases for siphash.c
+ *
+ * Copyright (C) 2015-2016 Jason A. Donenfeld <[email protected]>
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+
+/* Test vectors taken from official reference source available at:
+ * https://131002.net/siphash/siphash24.c
+ */
+static const u64 test_vectors[64] = {
+ 0x726fdb47dd0e0e31ULL, 0x74f839c593dc67fdULL, 0x0d6c8009d9a94f5aULL,
+ 0x85676696d7fb7e2dULL, 0xcf2794e0277187b7ULL, 0x18765564cd99a68dULL,
+ 0xcbc9466e58fee3ceULL, 0xab0200f58b01d137ULL, 0x93f5f5799a932462ULL,
+ 0x9e0082df0ba9e4b0ULL, 0x7a5dbbc594ddb9f3ULL, 0xf4b32f46226bada7ULL,
+ 0x751e8fbc860ee5fbULL, 0x14ea5627c0843d90ULL, 0xf723ca908e7af2eeULL,
+ 0xa129ca6149be45e5ULL, 0x3f2acc7f57c29bdbULL, 0x699ae9f52cbe4794ULL,
+ 0x4bc1b3f0968dd39cULL, 0xbb6dc91da77961bdULL, 0xbed65cf21aa2ee98ULL,
+ 0xd0f2cbb02e3b67c7ULL, 0x93536795e3a33e88ULL, 0xa80c038ccd5ccec8ULL,
+ 0xb8ad50c6f649af94ULL, 0xbce192de8a85b8eaULL, 0x17d835b85bbb15f3ULL,
+ 0x2f2e6163076bcfadULL, 0xde4daaaca71dc9a5ULL, 0xa6a2506687956571ULL,
+ 0xad87a3535c49ef28ULL, 0x32d892fad841c342ULL, 0x7127512f72f27cceULL,
+ 0xa7f32346f95978e3ULL, 0x12e0b01abb051238ULL, 0x15e034d40fa197aeULL,
+ 0x314dffbe0815a3b4ULL, 0x027990f029623981ULL, 0xcadcd4e59ef40c4dULL,
+ 0x9abfd8766a33735cULL, 0x0e3ea96b5304a7d0ULL, 0xad0c42d6fc585992ULL,
+ 0x187306c89bc215a9ULL, 0xd4a60abcf3792b95ULL, 0xf935451de4f21df2ULL,
+ 0xa9538f0419755787ULL, 0xdb9acddff56ca510ULL, 0xd06c98cd5c0975ebULL,
+ 0xe612a3cb9ecba951ULL, 0xc766e62cfcadaf96ULL, 0xee64435a9752fe72ULL,
+ 0xa192d576b245165aULL, 0x0a8787bf8ecb74b2ULL, 0x81b3e73d20b49b6fULL,
+ 0x7fa8220ba3b2eceaULL, 0x245731c13ca42499ULL, 0xb78dbfaf3a8d83bdULL,
+ 0xea1ad565322a1a0bULL, 0x60e61c23a3795013ULL, 0x6606d7e446282b93ULL,
+ 0x6ca4ecb15c5f91e1ULL, 0x9f626da15c9625f3ULL, 0xe51b38608ef25f57ULL,
+ 0x958a324ceb064572ULL
+};
+
+static int __init siphash_test_init(void)
+{
+ u8 in[64] __aligned(SIPHASH24_ALIGNMENT);
+ u8 k[16] __aligned(SIPHASH24_ALIGNMENT);
+ u8 in_unaligned[65];
+ u8 k_unaligned[65];
+ u8 i;
+ int ret = 0;
+
+ for (i = 0; i < 16; ++i) {
+ k[i] = i;
+ k_unaligned[i + 1] = i;
+ }
+ for (i = 0; i < 64; ++i) {
+ in[i] = i;
+ in_unaligned[i + 1] = i;
+ if (siphash24(in, i, k) != test_vectors[i]) {
+ pr_info("self-test aligned %u: FAIL\n", i + 1);
+ ret = -EINVAL;
+ }
+ if (siphash24_unaligned(in_unaligned + 1, i, k_unaligned + 1) != test_vectors[i]) {
+ pr_info("self-test unaligned %u: FAIL\n", i + 1);
+ ret = -EINVAL;
+ }
+ }
+ if (!ret)
+ pr_info("self-tests: pass\n");
+ return ret;
+}
+
+static void __exit siphash_test_exit(void)
+{
+}
+
+module_init(siphash_test_init);
+module_exit(siphash_test_exit);
+
+MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");
+MODULE_LICENSE("Dual BSD/GPL");
--
2.11.0
This gives a clear speed and security improvement. Siphash is both
faster and is more solid crypto than the aging MD5.
Rather than manually filling MD5 buffers, we simply create
a layout by a simple anonymous struct, for which gcc generates
rather efficient code.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: David Miller <[email protected]>
Cc: David Laight <[email protected]>
---
Changes from v2->v3:
- Structs are no longer packed, to mitigate slow byte-by-byte assignment.
- A typo has been fixed in the port number assignment.
net/core/secure_seq.c | 166 ++++++++++++++++++++++++++------------------------
1 file changed, 85 insertions(+), 81 deletions(-)
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 88a8e429fc3e..00eb141c981b 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -1,3 +1,5 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>. All Rights Reserved. */
+
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/cryptohash.h>
@@ -8,14 +10,14 @@
#include <linux/ktime.h>
#include <linux/string.h>
#include <linux/net.h>
-
+#include <linux/siphash.h>
#include <net/secure_seq.h>
#if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
+#include <linux/in6.h>
#include <net/tcp.h>
-#define NET_SECRET_SIZE (MD5_MESSAGE_BYTES / 4)
-static u32 net_secret[NET_SECRET_SIZE] ____cacheline_aligned;
+static u8 net_secret[SIPHASH24_KEY_LEN] __aligned(SIPHASH24_ALIGNMENT);
static __always_inline void net_secret_init(void)
{
@@ -44,44 +46,41 @@ static u32 seq_scale(u32 seq)
u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
__be16 sport, __be16 dport, u32 *tsoff)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
- u32 i;
-
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 sport;
+ __be16 dport;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .sport = sport,
+ .dport = dport
+ };
+ u64 hash;
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32)daddr[i];
- secret[4] = net_secret[4] +
- (((__force u16)sport << 16) + (__force u16)dport);
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- *tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
- return seq_scale(hash[0]);
+ hash = siphash24((const u8 *)&combined, offsetof(typeof(combined), end), net_secret);
+ *tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;
+ return seq_scale(hash);
}
EXPORT_SYMBOL(secure_tcpv6_sequence_number);
u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
__be16 dport)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
- u32 i;
-
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 dport;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .dport = dport
+ };
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32) daddr[i];
- secret[4] = net_secret[4] + (__force u32)dport;
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- return hash[0];
+ return siphash24((const u8 *)&combined, offsetof(typeof(combined), end), net_secret);
}
EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
#endif
@@ -91,33 +90,39 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport, u32 *tsoff)
{
- u32 hash[MD5_DIGEST_WORDS];
-
+ const struct {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 sport;
+ __be16 dport;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined = {
+ .saddr = saddr,
+ .daddr = daddr,
+ .sport = sport,
+ .dport = dport
+ };
+ u64 hash;
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- *tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
- return seq_scale(hash[0]);
+ hash = siphash24((const u8 *)&combined, offsetof(typeof(combined), end), net_secret);
+ *tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;
+ return seq_scale(hash);
}
u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
- u32 hash[MD5_DIGEST_WORDS];
-
+ const struct {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 dport;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined = {
+ .saddr = saddr,
+ .daddr = daddr,
+ .dport = dport
+ };
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = (__force u32)dport ^ net_secret[14];
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- return hash[0];
+ return siphash24((const u8 *)&combined, offsetof(typeof(combined), end), net_secret);
}
EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
#endif
@@ -126,21 +131,23 @@ EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport)
{
- u32 hash[MD5_DIGEST_WORDS];
+ const struct {
+ __be32 saddr;
+ __be32 daddr;
+ __be16 sport;
+ __be16 dport;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined = {
+ .saddr = saddr,
+ .daddr = daddr,
+ .sport = sport,
+ .dport = dport
+ };
u64 seq;
-
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- seq = hash[0] | (((u64)hash[1]) << 32);
+ seq = siphash24((const u8 *)&combined, offsetof(typeof(combined), end), net_secret);
seq += ktime_get_real_ns();
seq &= (1ull << 48) - 1;
-
return seq;
}
EXPORT_SYMBOL(secure_dccp_sequence_number);
@@ -149,26 +156,23 @@ EXPORT_SYMBOL(secure_dccp_sequence_number);
u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
__be16 sport, __be16 dport)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 sport;
+ __be16 dport;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .sport = sport,
+ .dport = dport
+ };
u64 seq;
- u32 i;
-
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32)daddr[i];
- secret[4] = net_secret[4] +
- (((__force u16)sport << 16) + (__force u16)dport);
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- seq = hash[0] | (((u64)hash[1]) << 32);
+ seq = siphash24((const u8 *)&combined, offsetof(typeof(combined), end), net_secret);
seq += ktime_get_real_ns();
seq &= (1ull << 48) - 1;
-
return seq;
}
EXPORT_SYMBOL(secure_dccpv6_sequence_number);
--
2.11.0
This duplicates the current algorithm for get_random_int/long, but uses
siphash24 instead. This comes with several benefits. It's certainly
faster and more cryptographically secure than MD5. This patch also
hashes the pid, entropy, and timestamp as fixed width fields, in order
to increase diffusion.
The previous md5 algorithm used a per-cpu md5 state, which caused
successive calls to the function to chain upon each other. While it's
not entirely clear that this kind of chaining is absolutely necessary
when using a secure PRF like siphash24, it can't hurt, and the timing of
the call chain does add a degree of natural entropy. So, in keeping with
this design, instead of the massive per-cpu 64-byte md5 state, there is
instead a per-cpu previously returned value for chaining.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Jean-Philippe Aumasson <[email protected]>
Cc: Ted Tso <[email protected]>
---
Changes from v2->v3:
- Structs are no longer packed, to mitigate slow byte-by-byte assignment.
drivers/char/random.c | 52 ++++++++++++++++++++++++++++++++-------------------
1 file changed, 33 insertions(+), 19 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index d6876d506220..b1c2e3b26430 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -262,6 +262,7 @@
#include <linux/syscalls.h>
#include <linux/completion.h>
#include <linux/uuid.h>
+#include <linux/siphash.h>
#include <crypto/chacha20.h>
#include <asm/processor.h>
@@ -2042,7 +2043,7 @@ struct ctl_table random_table[] = {
};
#endif /* CONFIG_SYSCTL */
-static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
+static u8 random_int_secret[SIPHASH24_KEY_LEN] __aligned(SIPHASH24_ALIGNMENT);
int random_int_secret_init(void)
{
@@ -2050,8 +2051,7 @@ int random_int_secret_init(void)
return 0;
}
-static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash)
- __aligned(sizeof(unsigned long));
+static DEFINE_PER_CPU(u64, get_random_int_chaining);
/*
* Get a random word for internal kernel use only. Similar to urandom but
@@ -2061,19 +2061,26 @@ static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash)
*/
unsigned int get_random_int(void)
{
- __u32 *hash;
unsigned int ret;
+ struct {
+ u64 chaining;
+ unsigned long ts;
+ unsigned long entropy;
+ pid_t pid;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined;
+ u64 *chaining;
if (arch_get_random_int(&ret))
return ret;
- hash = get_cpu_var(get_random_int_hash);
-
- hash[0] += current->pid + jiffies + random_get_entropy();
- md5_transform(hash, random_int_secret);
- ret = hash[0];
- put_cpu_var(get_random_int_hash);
-
+ chaining = get_cpu_ptr(&get_random_int_chaining);
+ combined.chaining = *chaining;
+ combined.ts = jiffies;
+ combined.entropy = random_get_entropy();
+ combined.pid = current->pid;
+ ret = *chaining = siphash24((u8 *)&combined, offsetof(typeof(combined), end), random_int_secret);
+ put_cpu_ptr(chaining);
return ret;
}
EXPORT_SYMBOL(get_random_int);
@@ -2083,19 +2090,26 @@ EXPORT_SYMBOL(get_random_int);
*/
unsigned long get_random_long(void)
{
- __u32 *hash;
unsigned long ret;
+ struct {
+ u64 chaining;
+ unsigned long ts;
+ unsigned long entropy;
+ pid_t pid;
+ char end[];
+ } __aligned(SIPHASH24_ALIGNMENT) combined;
+ u64 *chaining;
if (arch_get_random_long(&ret))
return ret;
- hash = get_cpu_var(get_random_int_hash);
-
- hash[0] += current->pid + jiffies + random_get_entropy();
- md5_transform(hash, random_int_secret);
- ret = *(unsigned long *)hash;
- put_cpu_var(get_random_int_hash);
-
+ chaining = get_cpu_ptr(&get_random_int_chaining);
+ combined.chaining = *chaining;
+ combined.ts = jiffies;
+ combined.entropy = random_get_entropy();
+ combined.pid = current->pid;
+ ret = *chaining = siphash24((u8 *)&combined, offsetof(typeof(combined), end), random_int_secret);
+ put_cpu_ptr(chaining);
return ret;
}
EXPORT_SYMBOL(get_random_long);
--
2.11.0
On Wed, Dec 14, 2016 at 10:46 AM, Jason A. Donenfeld <[email protected]> wrote:
> SipHash is a 64-bit keyed hash function that is actually a
> cryptographically secure PRF, like HMAC. Except SipHash is super fast,
> and is meant to be used as a hashtable keyed lookup function.
>
"super fast" is relative. My quick test shows that this faster than
Toeplitz (good, but not exactly hard to achieve), but is about 4x
slower than jhash.
> SipHash isn't just some new trendy hash function. It's been around for a
> while, and there really isn't anything that comes remotely close to
> being useful in the way SipHash is. With that said, why do we need this?
>
I don't think we need advertising nor a lesson on hashing. It would be
much more useful if you just point us to the paper on siphash (which I
assume I http://cr.yp.to/siphash/siphash-20120918.pdf ?).
> There are a variety of attacks known as "hashtable poisoning" in which an
> attacker forms some data such that the hash of that data will be the
> same, and then preceeds to fill up all entries of a hashbucket. This is
> a realistic and well-known denial-of-service vector.
>
> Linux developers already seem to be aware that this is an issue, and
> various places that use hash tables in, say, a network context, use a
> non-cryptographically secure function (usually jhash) and then try to
> twiddle with the key on a time basis (or in many cases just do nothing
> and hope that nobody notices). While this is an admirable attempt at
> solving the problem, it doesn't actually fix it. SipHash fixes it.
>
Key rotation is important anyway, without any key rotation even if the
key is compromised in siphash by some external means we would have an
insecure hash until the system reboots.
> (It fixes it in such a sound way that you could even build a stream
> cipher out of SipHash that would resist the modern cryptanalysis.)
>
> There are a modicum of places in the kernel that are vulnerable to
> hashtable poisoning attacks, either via userspace vectors or network
> vectors, and there's not a reliable mechanism inside the kernel at the
> moment to fix it. The first step toward fixing these issues is actually
> getting a secure primitive into the kernel for developers to use. Then
> we can, bit by bit, port things over to it as deemed appropriate.
>
> Secondly, a few places are using MD5 for creating secure sequence
> numbers, port numbers, or fast random numbers. Siphash is a faster, more
> fittting, and more secure replacement for MD5 in those situations.
>
> Dozens of languages are already using this internally for their hash
> tables. Some of the BSDs already use this in their kernels. SipHash is
> a widely known high-speed solution to a widely known problem, and it's
> time we catch-up.
>
Maybe so, but we need to do due diligence before considering adopting
siphash as the primary hashing in the network stack. Consider that we
may very well perform a hash over L4 tuples on _every_ packet. We've
done a good job at limiting this to be at most one hash per packet,
but nevertheless the performance of the hash function must be take
into account.
A few points:
1) My quick test shows siphash is about four times more expensive than
jhash. On my test system, computing a hash over IPv4 tuple (two 32 bit
addresses and 2 16 bit source ports) is 6.9 nsecs in Jenkins hash, 33
nsecs with siphash. Given that we have eliminated most of the packet
header hashes this might be tolerable, but still should be looking at
ways to optimize.
2) I like moving to use u64 (quad words) in the hash, this is an
improvement over Jenkins which is based on 32 bit words. If we put
this in the kernel we probably want to have several variants of
siphash for specific sizes (e.g. siphash1, siphash2, siphash2,
siphashn for hash over one, two, three, or n sixty four bit words).
3) I also tested siphash distribution and Avalanche Effect (these
really should have been covered in the paper :-( ). Both of these are
good with siphash, in fact almost have identical characteristics to
Jenkins hash.
Tom
> Signed-off-by: Jason A. Donenfeld <[email protected]>
> Cc: Jean-Philippe Aumasson <[email protected]>
> Cc: Daniel J. Bernstein <[email protected]>
> Cc: Linus Torvalds <[email protected]>
> Cc: Eric Biggers <[email protected]>
> Cc: David Laight <[email protected]>
> ---
> Changes from v2->v3:
>
> - There is now a fast aligned version of the function and a not-as-fast
> unaligned version. The requirements for each have been documented in
> a docbook-style comment. As well, the header now contains a constant
> for the expected alignment.
>
> - The test suite has been updated to check both the unaligned and aligned
> version of the function.
>
> include/linux/siphash.h | 30 ++++++++++
> lib/Kconfig.debug | 6 +-
> lib/Makefile | 5 +-
> lib/siphash.c | 153 ++++++++++++++++++++++++++++++++++++++++++++++++
> lib/test_siphash.c | 85 +++++++++++++++++++++++++++
> 5 files changed, 274 insertions(+), 5 deletions(-)
> create mode 100644 include/linux/siphash.h
> create mode 100644 lib/siphash.c
> create mode 100644 lib/test_siphash.c
>
> diff --git a/include/linux/siphash.h b/include/linux/siphash.h
> new file mode 100644
> index 000000000000..82dc1a911a2e
> --- /dev/null
> +++ b/include/linux/siphash.h
> @@ -0,0 +1,30 @@
> +/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>
> + *
> + * This file is provided under a dual BSD/GPLv2 license.
> + *
> + * SipHash: a fast short-input PRF
> + * https://131002.net/siphash/
> + */
> +
> +#ifndef _LINUX_SIPHASH_H
> +#define _LINUX_SIPHASH_H
> +
> +#include <linux/types.h>
> +
> +enum siphash_lengths {
> + SIPHASH24_KEY_LEN = 16,
> + SIPHASH24_ALIGNMENT = 8
> +};
> +
> +u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN]);
> +
> +#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> +static inline u64 siphash24_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
> +{
> + return siphash24(data, len, key);
> +}
> +#else
> +u64 siphash24_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN]);
> +#endif
> +
> +#endif /* _LINUX_SIPHASH_H */
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index e6327d102184..32bbf689fc46 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -1843,9 +1843,9 @@ config TEST_HASH
> tristate "Perform selftest on hash functions"
> default n
> help
> - Enable this option to test the kernel's integer (<linux/hash,h>)
> - and string (<linux/stringhash.h>) hash functions on boot
> - (or module load).
> + Enable this option to test the kernel's integer (<linux/hash.h>),
> + string (<linux/stringhash.h>), and siphash (<linux/siphash.h>)
> + hash functions on boot (or module load).
>
> This is intended to help people writing architecture-specific
> optimized versions. If unsure, say N.
> diff --git a/lib/Makefile b/lib/Makefile
> index 50144a3aeebd..71d398b04a74 100644
> --- a/lib/Makefile
> +++ b/lib/Makefile
> @@ -22,7 +22,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
> sha1.o chacha20.o md5.o irq_regs.o argv_split.o \
> flex_proportions.o ratelimit.o show_mem.o \
> is_single_threaded.o plist.o decompress.o kobject_uevent.o \
> - earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
> + earlycpio.o seq_buf.o siphash.o \
> + nmi_backtrace.o nodemask.o win_minmax.o
>
> lib-$(CONFIG_MMU) += ioremap.o
> lib-$(CONFIG_SMP) += cpumask.o
> @@ -44,7 +45,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
> obj-y += kstrtox.o
> obj-$(CONFIG_TEST_BPF) += test_bpf.o
> obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
> -obj-$(CONFIG_TEST_HASH) += test_hash.o
> +obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
> obj-$(CONFIG_TEST_KASAN) += test_kasan.o
> obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
> obj-$(CONFIG_TEST_LKM) += test_module.o
> diff --git a/lib/siphash.c b/lib/siphash.c
> new file mode 100644
> index 000000000000..32acdc26234f
> --- /dev/null
> +++ b/lib/siphash.c
> @@ -0,0 +1,153 @@
> +/* Copyright (C) 2015-2016 Jason A. Donenfeld <[email protected]>
> + * Copyright (C) 2012-2014 Jean-Philippe Aumasson <[email protected]>
> + * Copyright (C) 2012-2014 Daniel J. Bernstein <[email protected]>
> + *
> + * This file is provided under a dual BSD/GPLv2 license.
> + *
> + * SipHash: a fast short-input PRF
> + * https://131002.net/siphash/
> + */
> +
> +#include <linux/siphash.h>
> +#include <linux/kernel.h>
> +#include <asm/unaligned.h>
> +
> +#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
> +#include <linux/dcache.h>
> +#include <asm/word-at-a-time.h>
> +#endif
> +
> +#define SIPROUND \
> + do { \
> + v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
> + v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
> + v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
> + v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
> + } while(0)
> +
> +static inline u16 le16_to_cpuvp(const void *p)
> +{
> + return le16_to_cpup(p);
> +}
> +static inline u32 le32_to_cpuvp(const void *p)
> +{
> + return le32_to_cpup(p);
> +}
> +static inline u64 le64_to_cpuvp(const void *p)
> +{
> + return le64_to_cpup(p);
> +}
> +
> +/**
> + * siphash24 - compute 64-bit siphash24 PRF value
> + * @data: buffer to hash, must be aligned to SIPHASH24_ALIGNMENT
> + * @size: size of @data
> + * @key: key buffer of size SIPHASH24_KEY_LEN, must be aligned to SIPHASH24_ALIGNMENT
> + */
> +u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
> +{
> + u64 v0 = 0x736f6d6570736575ULL;
> + u64 v1 = 0x646f72616e646f6dULL;
> + u64 v2 = 0x6c7967656e657261ULL;
> + u64 v3 = 0x7465646279746573ULL;
> + u64 b = ((u64)len) << 56;
> + u64 k0 = le64_to_cpuvp(key);
> + u64 k1 = le64_to_cpuvp(key + sizeof(u64));
> + u64 m;
> + const u8 *end = data + len - (len % sizeof(u64));
> + const u8 left = len & (sizeof(u64) - 1);
> + v3 ^= k1;
> + v2 ^= k0;
> + v1 ^= k1;
> + v0 ^= k0;
> + for (; data != end; data += sizeof(u64)) {
> + m = le64_to_cpuvp(data);
> + v3 ^= m;
> + SIPROUND;
> + SIPROUND;
> + v0 ^= m;
> + }
> +#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
> + if (left)
> + b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
> +#else
> + switch (left) {
> + case 7: b |= ((u64)data[6]) << 48;
> + case 6: b |= ((u64)data[5]) << 40;
> + case 5: b |= ((u64)data[4]) << 32;
> + case 4: b |= le32_to_cpuvp(data); break;
> + case 3: b |= ((u64)data[2]) << 16;
> + case 2: b |= le16_to_cpuvp(data); break;
> + case 1: b |= data[0];
> + }
> +#endif
> + v3 ^= b;
> + SIPROUND;
> + SIPROUND;
> + v0 ^= b;
> + v2 ^= 0xff;
> + SIPROUND;
> + SIPROUND;
> + SIPROUND;
> + SIPROUND;
> + return (v0 ^ v1) ^ (v2 ^ v3);
> +}
> +EXPORT_SYMBOL(siphash24);
> +
> +#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
> +/**
> + * siphash24 - compute 64-bit siphash24 PRF value, without alignment requirements
> + * @data: buffer to hash
> + * @size: size of @data
> + * @key: key buffer of size SIPHASH24_KEY_LEN
> + */
> +u64 siphash24_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
> +{
> + u64 v0 = 0x736f6d6570736575ULL;
> + u64 v1 = 0x646f72616e646f6dULL;
> + u64 v2 = 0x6c7967656e657261ULL;
> + u64 v3 = 0x7465646279746573ULL;
> + u64 b = ((u64)len) << 56;
> + u64 k0 = get_unaligned_le64(key);
> + u64 k1 = get_unaligned_le64(key + sizeof(u64));
> + u64 m;
> + const u8 *end = data + len - (len % sizeof(u64));
> + const u8 left = len & (sizeof(u64) - 1);
> + v3 ^= k1;
> + v2 ^= k0;
> + v1 ^= k1;
> + v0 ^= k0;
> + for (; data != end; data += sizeof(u64)) {
> + m = get_unaligned_le64(data);
> + v3 ^= m;
> + SIPROUND;
> + SIPROUND;
> + v0 ^= m;
> + }
> +#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
> + if (left)
> + b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
> +#else
> + switch (left) {
> + case 7: b |= ((u64)data[6]) << 48;
> + case 6: b |= ((u64)data[5]) << 40;
> + case 5: b |= ((u64)data[4]) << 32;
> + case 4: b |= get_unaligned_le32(data); break;
> + case 3: b |= ((u64)data[2]) << 16;
> + case 2: b |= get_unaligned_le16(data); break;
> + case 1: b |= data[0];
> + }
> +#endif
> + v3 ^= b;
> + SIPROUND;
> + SIPROUND;
> + v0 ^= b;
> + v2 ^= 0xff;
> + SIPROUND;
> + SIPROUND;
> + SIPROUND;
> + SIPROUND;
> + return (v0 ^ v1) ^ (v2 ^ v3);
> +}
> +EXPORT_SYMBOL(siphash24_unaligned);
> +#endif
> diff --git a/lib/test_siphash.c b/lib/test_siphash.c
> new file mode 100644
> index 000000000000..69ac94dec366
> --- /dev/null
> +++ b/lib/test_siphash.c
> @@ -0,0 +1,85 @@
> +/* Test cases for siphash.c
> + *
> + * Copyright (C) 2015-2016 Jason A. Donenfeld <[email protected]>
> + *
> + * This file is provided under a dual BSD/GPLv2 license.
> + *
> + * SipHash: a fast short-input PRF
> + * https://131002.net/siphash/
> + */
> +
> +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
> +
> +#include <linux/siphash.h>
> +#include <linux/kernel.h>
> +#include <linux/string.h>
> +#include <linux/errno.h>
> +#include <linux/module.h>
> +
> +/* Test vectors taken from official reference source available at:
> + * https://131002.net/siphash/siphash24.c
> + */
> +static const u64 test_vectors[64] = {
> + 0x726fdb47dd0e0e31ULL, 0x74f839c593dc67fdULL, 0x0d6c8009d9a94f5aULL,
> + 0x85676696d7fb7e2dULL, 0xcf2794e0277187b7ULL, 0x18765564cd99a68dULL,
> + 0xcbc9466e58fee3ceULL, 0xab0200f58b01d137ULL, 0x93f5f5799a932462ULL,
> + 0x9e0082df0ba9e4b0ULL, 0x7a5dbbc594ddb9f3ULL, 0xf4b32f46226bada7ULL,
> + 0x751e8fbc860ee5fbULL, 0x14ea5627c0843d90ULL, 0xf723ca908e7af2eeULL,
> + 0xa129ca6149be45e5ULL, 0x3f2acc7f57c29bdbULL, 0x699ae9f52cbe4794ULL,
> + 0x4bc1b3f0968dd39cULL, 0xbb6dc91da77961bdULL, 0xbed65cf21aa2ee98ULL,
> + 0xd0f2cbb02e3b67c7ULL, 0x93536795e3a33e88ULL, 0xa80c038ccd5ccec8ULL,
> + 0xb8ad50c6f649af94ULL, 0xbce192de8a85b8eaULL, 0x17d835b85bbb15f3ULL,
> + 0x2f2e6163076bcfadULL, 0xde4daaaca71dc9a5ULL, 0xa6a2506687956571ULL,
> + 0xad87a3535c49ef28ULL, 0x32d892fad841c342ULL, 0x7127512f72f27cceULL,
> + 0xa7f32346f95978e3ULL, 0x12e0b01abb051238ULL, 0x15e034d40fa197aeULL,
> + 0x314dffbe0815a3b4ULL, 0x027990f029623981ULL, 0xcadcd4e59ef40c4dULL,
> + 0x9abfd8766a33735cULL, 0x0e3ea96b5304a7d0ULL, 0xad0c42d6fc585992ULL,
> + 0x187306c89bc215a9ULL, 0xd4a60abcf3792b95ULL, 0xf935451de4f21df2ULL,
> + 0xa9538f0419755787ULL, 0xdb9acddff56ca510ULL, 0xd06c98cd5c0975ebULL,
> + 0xe612a3cb9ecba951ULL, 0xc766e62cfcadaf96ULL, 0xee64435a9752fe72ULL,
> + 0xa192d576b245165aULL, 0x0a8787bf8ecb74b2ULL, 0x81b3e73d20b49b6fULL,
> + 0x7fa8220ba3b2eceaULL, 0x245731c13ca42499ULL, 0xb78dbfaf3a8d83bdULL,
> + 0xea1ad565322a1a0bULL, 0x60e61c23a3795013ULL, 0x6606d7e446282b93ULL,
> + 0x6ca4ecb15c5f91e1ULL, 0x9f626da15c9625f3ULL, 0xe51b38608ef25f57ULL,
> + 0x958a324ceb064572ULL
> +};
> +
> +static int __init siphash_test_init(void)
> +{
> + u8 in[64] __aligned(SIPHASH24_ALIGNMENT);
> + u8 k[16] __aligned(SIPHASH24_ALIGNMENT);
> + u8 in_unaligned[65];
> + u8 k_unaligned[65];
> + u8 i;
> + int ret = 0;
> +
> + for (i = 0; i < 16; ++i) {
> + k[i] = i;
> + k_unaligned[i + 1] = i;
> + }
> + for (i = 0; i < 64; ++i) {
> + in[i] = i;
> + in_unaligned[i + 1] = i;
> + if (siphash24(in, i, k) != test_vectors[i]) {
> + pr_info("self-test aligned %u: FAIL\n", i + 1);
> + ret = -EINVAL;
> + }
> + if (siphash24_unaligned(in_unaligned + 1, i, k_unaligned + 1) != test_vectors[i]) {
> + pr_info("self-test unaligned %u: FAIL\n", i + 1);
> + ret = -EINVAL;
> + }
> + }
> + if (!ret)
> + pr_info("self-tests: pass\n");
> + return ret;
> +}
> +
> +static void __exit siphash_test_exit(void)
> +{
> +}
> +
> +module_init(siphash_test_init);
> +module_exit(siphash_test_exit);
> +
> +MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");
> +MODULE_LICENSE("Dual BSD/GPL");
> --
> 2.11.0
>
On 14.12.2016 19:06, Jason A. Donenfeld wrote:
> Hi David,
>
> On Wed, Dec 14, 2016 at 6:56 PM, David Miller <[email protected]> wrote:
>> Just marking the structure __packed, whether necessary or not, makes
>> the compiler assume that the members are not aligned and causes
>> byte-by-byte accesses to be performed for words.
>> Never, _ever_, use __packed unless absolutely necessary, it pessimizes
>> the code on cpus that require proper alignment of types.
>
> Oh, jimminy cricket, I did not realize that it made assignments
> byte-by-byte *always*. So what options am I left with? What
> immediately comes to mind are:
>
> 1)
>
> struct {
> u64 a;
> u32 b;
> u32 c;
> u16 d;
> u8 end[];
I don't think this helps. Did you test it? I don't see reason why
padding could be left out between `d' and `end' because of the flexible
array member?
Bye,
Hannes
Hi Tom,
On Wed, Dec 14, 2016 at 8:18 PM, Tom Herbert <[email protected]> wrote:
> "super fast" is relative. My quick test shows that this faster than
> Toeplitz (good, but not exactly hard to achieve), but is about 4x
> slower than jhash.
Fast relative to other cryptographically secure PRFs.
>> SipHash isn't just some new trendy hash function. It's been around for a
>> while, and there really isn't anything that comes remotely close to
>> being useful in the way SipHash is. With that said, why do we need this?
> I don't think we need advertising nor a lesson on hashing. It would be
> much more useful if you just point us to the paper on siphash (which I
> assume I http://cr.yp.to/siphash/siphash-20120918.pdf ?).
Ugh. Sorry. It definitely wasn't my intention to give an uninvited
lesson or an annoying advert. For the former, I didn't want to make
any expectations about fields of knowledge, because I honest have no
idea. For the latter, I wrote that sentence to indicate that siphash
isn't just some newfangled hipster function, but something useful and
well established. I didn't mean it as a form of advertising. My
apologies if I've offended your sensibilities.
That cr.yp.to link is fine, or https://131002.net/siphash/siphash.pdf I believe.
> Key rotation is important anyway, without any key rotation even if the
> key is compromised in siphash by some external means we would have an
> insecure hash until the system reboots.
I'm a bit surprised to read this. I've never designed a system to be
secure even in the event of remote arbitrary kernel memory disclosure,
and I wasn't aware this was generally considered an architectural
requirement or Linux.
In any case, if you want this, I suppose you can have it with siphash too.
> Maybe so, but we need to do due diligence before considering adopting
> siphash as the primary hashing in the network stack. Consider that we
> may very well perform a hash over L4 tuples on _every_ packet. We've
> done a good job at limiting this to be at most one hash per packet,
> but nevertheless the performance of the hash function must be take
> into account.
I agree with you. It seems like each case is going to needed to be
measured on a case by case basis. In this series I make the first use
of siphash in the secure sequence generation and get_random_int/long,
where siphash replaces md5, so there's a pretty clear performance in.
But for the jhash replacements indeed things are going to need to be
individually evaluated.
> 1) My quick test shows siphash is about four times more expensive than
> jhash. On my test system, computing a hash over IPv4 tuple (two 32 bit
> addresses and 2 16 bit source ports) is 6.9 nsecs in Jenkins hash, 33
> nsecs with siphash. Given that we have eliminated most of the packet
> header hashes this might be tolerable, but still should be looking at
> ways to optimize.
> 2) I like moving to use u64 (quad words) in the hash, this is an
> improvement over Jenkins which is based on 32 bit words. If we put
> this in the kernel we probably want to have several variants of
> siphash for specific sizes (e.g. siphash1, siphash2, siphash2,
> siphashn for hash over one, two, three, or n sixty four bit words).
I think your suggestion for (2) will contribute to further
optimizations for (1). In v2, I had another patch in there adding
siphash_1word, siphash_2words, etc, like jhash, but I implemented it
by taking u32 variables and then just concatenating these into a
buffer and passing them to the main siphash function. I removed it
from v3 because I thought that these kind of missed the whole point.
In particular:
a) siphash24_1word, siphash24_2words, siphash24_3words, etc should
take u64, not u32, since that's what siphash operates on natively
b) Rather than concatenating them in a buffer, I should write
specializations of the siphash24 function _especially_ for these size
inputs to avoid the copy and to reduce the book keeping.
I'll add these functions to v4 implemented like that.
Thanks for the useful feedback and benchmarks!
Jason
Hi Hannes,
On Wed, Dec 14, 2016 at 8:22 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> I don't think this helps. Did you test it? I don't see reason why
> padding could be left out between `d' and `end' because of the flexible
> array member?
Because the type u8 doesn't require any alignment requirements, it can
nestle right up there cozy with the u16:
zx2c4@thinkpad ~ $ cat a.c
#include <stdint.h>
#include <stdio.h>
#include <stddef.h>
int main()
{
struct {
uint64_t a;
uint32_t b;
uint32_t c;
uint16_t d;
char x[];
} a;
printf("%zu\n", sizeof(a));
printf("%zu\n", offsetof(typeof(a), x));
return 0;
}
zx2c4@thinkpad ~ $ gcc a.c
zx2c4@thinkpad ~ $ ./a.out
24
18
Jason
Hi Hannes,
On Wed, Dec 14, 2016 at 4:09 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> Yes, numbers would be very usable here. I am mostly concerned about
> small plastic router cases. E.g. assume you double packet processing
> time with a change of the hashing function at what point is the actual
> packet processing more of an attack vector than the hashtable?
I agree. Looks like Tom did some very quick benchmarks. I'll do some
more precise benchmarks myself when we graduate from looking at md5
replacement (the easy case) to looking at jhash replacement (the
harder case).
>> With that said, siphash is here to replace uses of jhash where
>> hashtable poisoning vulnerabilities make it necessary. Where there's
>> no significant security improvement, if there's no speed improvement
>> either, then of course nothing's going to change.
>
> It still changes currently well working source. ;-)
I mean if siphash doesn't make things better in someway, we'll just
continue using jhash, so no source change or anything. In other words:
evolutionary conservative approach rather than hasty "replace 'em
all!" tomfoolery.
> MD5 is considered broken because its collision resistance is broken?
> SipHash doesn't even claim to have collision resistance (which we don't
> need here)?
Not just that, but it's not immediately clear to me that using MD5 as
a PRF the way it is now with md5_transform is even a straightforwardly
good idea.
> But I agree, certainly it could be a nice speed-up!
The benchmarks for the secure sequence number generation and the rng
are indeed really promising.
> I think you mean non-linearity.
Yea of course, editing typo, sorry.
> In general I am in favor to switch to siphash, but it would be nice to
> see some benchmarks with the specific kernel implementation also on some
> smaller 32 bit CPUs and especially without using any SIMD instructions
> (which might have been used in paper comparison).
Sure, agreed. Each proposed jhash replacement will need to be
benchmarked on little MIPS machines and x86 monsters alike, with
patches indicating PPS before and after.
Jason
On Wed, Dec 14, 2016 at 4:53 AM, Jason A. Donenfeld <[email protected]> wrote:
> Hi David,
>
> On Wed, Dec 14, 2016 at 10:51 AM, David Laight <[email protected]> wrote:
>> From: Jason A. Donenfeld
>>> Sent: 14 December 2016 00:17
>>> This gives a clear speed and security improvement. Rather than manually
>>> filling MD5 buffers, we simply create a layout by a simple anonymous
>>> struct, for which gcc generates rather efficient code.
>> ...
>>> + const struct {
>>> + struct in6_addr saddr;
>>> + struct in6_addr daddr;
>>> + __be16 sport;
>>> + __be16 dport;
>>> + } __packed combined = {
>>> + .saddr = *(struct in6_addr *)saddr,
>>> + .daddr = *(struct in6_addr *)daddr,
>>> + .sport = sport,
>>> + .dport = dport
>>> + };
>>
>> You need to look at the effect of marking this (and the other)
>> structures 'packed' on architectures like sparc64.
>
> In all current uses of __packed in the code, I think the impact is
> precisely zero, because all structures have members in descending
> order of size, with each member being a perfect multiple of the one
> below it. The __packed is therefore just there for safety, in case
> somebody comes in and screws everything up by sticking a u8 in
> between. In that case, it wouldn't be desirable to hash the structure
> padding bits. In the worst case, I don't believe the impact would be
> worse than a byte-by-byte memcpy, which is what the old code did. But
> anyway, these structures are already naturally packed anyway, so the
> present impact is nil.
>
If you pad the data structure to 64 bits then we can call the version
of siphash that only deals in 64 bit words. Writing a zero in the
padding will be cheaper than dealing with odd lengths in siphash24.
Tom
> Jason
Hey Jason,
On 14.12.2016 20:38, Jason A. Donenfeld wrote:
> On Wed, Dec 14, 2016 at 8:22 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
>> I don't think this helps. Did you test it? I don't see reason why
>> padding could be left out between `d' and `end' because of the flexible
>> array member?
>
> Because the type u8 doesn't require any alignment requirements, it can
> nestle right up there cozy with the u16:
>
> zx2c4@thinkpad ~ $ cat a.c
> #include <stdint.h>
> #include <stdio.h>
> #include <stddef.h>
> int main()
> {
> struct {
> uint64_t a;
> uint32_t b;
> uint32_t c;
> uint16_t d;
> char x[];
> } a;
> printf("%zu\n", sizeof(a));
> printf("%zu\n", offsetof(typeof(a), x));
> return 0;
> }
> zx2c4@thinkpad ~ $ gcc a.c
> zx2c4@thinkpad ~ $ ./a.out
> 24
> 18
Sorry, I misread the patch. You are using offsetof. In this case remove
the char x[] and just use offsetofend because it is misleading
otherwise. Should work like that though.
What I don't really understand is that the addition of this complexity
actually reduces the performance, as you have to take the "if (left)"
branch during hashing and causes you to make a load_unaligned_zeropad.
Bye,
Hannes
Hey Tom,
Just following up on what I mentioned in my last email...
On Wed, Dec 14, 2016 at 8:35 PM, Jason A. Donenfeld <[email protected]> wrote:
> I think your suggestion for (2) will contribute to further
> optimizations for (1). In v2, I had another patch in there adding
> siphash_1word, siphash_2words, etc, like jhash, but I implemented it
> by taking u32 variables and then just concatenating these into a
> buffer and passing them to the main siphash function. I removed it
> from v3 because I thought that these kind of missed the whole point.
> In particular:
>
> a) siphash24_1word, siphash24_2words, siphash24_3words, etc should
> take u64, not u32, since that's what siphash operates on natively
I implemented these here:
https://git.zx2c4.com/linux-dev/commit/?h=siphash&id=4652b6f3643bdba217e2194d89661348bbac48a0
This will be part of the next version of the series I submit. It's not
immediately clear that using it is strictly faster than the struct
trick though. However, I'm not yet sure why this would be.
Jason
On Wed, Dec 14, 2016 at 9:12 PM, Tom Herbert <[email protected]> wrote:
> If you pad the data structure to 64 bits then we can call the version
> of siphash that only deals in 64 bit words. Writing a zero in the
> padding will be cheaper than dealing with odd lengths in siphash24.
On Wed, Dec 14, 2016 at 9:27 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> What I don't really understand is that the addition of this complexity
> actually reduces the performance, as you have to take the "if (left)"
> branch during hashing and causes you to make a load_unaligned_zeropad.
Oh, duh, you guys are right. Fixed in my repo [1]. I'll submit the
next version in a day or so to let some other comments come in.
Thanks again for your reviews.
Jason
[1] https://git.zx2c4.com/linux-dev/log/?h=siphash
Hi Jason,
[auto build test ERROR on linus/master]
[also build test ERROR on v4.9 next-20161214]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Jason-A-Donenfeld/siphash-add-cryptographically-secure-hashtable-function/20161215-041458
config: i386-randconfig-i1-201650 (attached as .config)
compiler: gcc-4.8 (Debian 4.8.4-1) 4.8.4
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All errors (new ones prefixed by >>):
lib/test_siphash.c: In function 'siphash_test_init':
>> lib/test_siphash.c:49:2: error: requested alignment is not an integer constant
u8 in[64] __aligned(SIPHASH24_ALIGNMENT);
^
lib/test_siphash.c:50:2: error: requested alignment is not an integer constant
u8 k[16] __aligned(SIPHASH24_ALIGNMENT);
^
vim +49 lib/test_siphash.c
43 0x6ca4ecb15c5f91e1ULL, 0x9f626da15c9625f3ULL, 0xe51b38608ef25f57ULL,
44 0x958a324ceb064572ULL
45 };
46
47 static int __init siphash_test_init(void)
48 {
> 49 u8 in[64] __aligned(SIPHASH24_ALIGNMENT);
50 u8 k[16] __aligned(SIPHASH24_ALIGNMENT);
51 u8 in_unaligned[65];
52 u8 k_unaligned[65];
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Interesting. Evidently gcc 4.8 doesn't like my use of:
enum siphash_lengths {
SIPHASH24_KEY_LEN = 16,
SIPHASH24_ALIGNMENT = 8
};
I'll convert this to the more boring:
#define SIPHASH24_KEY_LEN 16
#define SIPHASH24_ALIGNMENT 8
On Wed, Dec 14, 2016 at 12:55 PM, Jason A. Donenfeld <[email protected]> wrote:
> Hey Tom,
>
> Just following up on what I mentioned in my last email...
>
> On Wed, Dec 14, 2016 at 8:35 PM, Jason A. Donenfeld <[email protected]> wrote:
>> I think your suggestion for (2) will contribute to further
>> optimizations for (1). In v2, I had another patch in there adding
>> siphash_1word, siphash_2words, etc, like jhash, but I implemented it
>> by taking u32 variables and then just concatenating these into a
>> buffer and passing them to the main siphash function. I removed it
>> from v3 because I thought that these kind of missed the whole point.
>> In particular:
>>
>> a) siphash24_1word, siphash24_2words, siphash24_3words, etc should
>> take u64, not u32, since that's what siphash operates on natively
>
> I implemented these here:
> https://git.zx2c4.com/linux-dev/commit/?h=siphash&id=4652b6f3643bdba217e2194d89661348bbac48a0
>
Those look good, although I would probably just do 1,2,3 words and
then have a function that takes n words like jhash. Might want to call
these dword to distinguish from 32 bit words in jhash.
Also, what is the significance of "24" in the function and constant
names? Can we just drop that and call this siphash?
Tom
> This will be part of the next version of the series I submit. It's not
> immediately clear that using it is strictly faster than the struct
> trick though. However, I'm not yet sure why this would be.
>
> Jason
Hi Jason,
[auto build test ERROR on linus/master]
[also build test ERROR on next-20161214]
[cannot apply to v4.9]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Jason-A-Donenfeld/siphash-add-cryptographically-secure-hashtable-function/20161215-041458
config: openrisc-or1ksim_defconfig (attached as .config)
compiler: or32-linux-gcc (GCC) 4.5.1-or32-1.0rc1
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=openrisc
All errors (new ones prefixed by >>):
>> net/core/secure_seq.c:20:1: error: requested alignment is not a constant
net/core/secure_seq.c: In function 'secure_tcp_sequence_number':
net/core/secure_seq.c:99:2: error: requested alignment is not a constant
net/core/secure_seq.c: In function 'secure_ipv4_port_ephemeral':
net/core/secure_seq.c:119:2: error: requested alignment is not a constant
vim +20 net/core/secure_seq.c
14 #include <net/secure_seq.h>
15
16 #if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
17 #include <linux/in6.h>
18 #include <net/tcp.h>
19
> 20 static u8 net_secret[SIPHASH24_KEY_LEN] __aligned(SIPHASH24_ALIGNMENT);
21
22 static __always_inline void net_secret_init(void)
23 {
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Hi Jason,
[auto build test ERROR on linus/master]
[also build test ERROR on next-20161214]
[cannot apply to v4.9]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Jason-A-Donenfeld/siphash-add-cryptographically-secure-hashtable-function/20161215-041458
config: i386-randconfig-i1-201650 (attached as .config)
compiler: gcc-4.8 (Debian 4.8.4-1) 4.8.4
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All errors (new ones prefixed by >>):
>> drivers/char/random.c:2046:1: error: requested alignment is not an integer constant
static u8 random_int_secret[SIPHASH24_KEY_LEN] __aligned(SIPHASH24_ALIGNMENT);
^
drivers/char/random.c: In function 'get_random_int':
drivers/char/random.c:2071:2: error: requested alignment is not an integer constant
} __aligned(SIPHASH24_ALIGNMENT) combined;
^
drivers/char/random.c: In function 'get_random_long':
drivers/char/random.c:2100:2: error: requested alignment is not an integer constant
} __aligned(SIPHASH24_ALIGNMENT) combined;
^
vim +2046 drivers/char/random.c
2040 },
2041 #endif
2042 { }
2043 };
2044 #endif /* CONFIG_SYSCTL */
2045
> 2046 static u8 random_int_secret[SIPHASH24_KEY_LEN] __aligned(SIPHASH24_ALIGNMENT);
2047
2048 int random_int_secret_init(void)
2049 {
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Hi Jason,
[auto build test ERROR on linus/master]
[also build test ERROR on next-20161214]
[cannot apply to v4.9]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Jason-A-Donenfeld/siphash-add-cryptographically-secure-hashtable-function/20161215-041458
config: openrisc-or1ksim_defconfig (attached as .config)
compiler: or32-linux-gcc (GCC) 4.5.1-or32-1.0rc1
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=openrisc
All errors (new ones prefixed by >>):
>> drivers/char/random.c:2046:1: error: requested alignment is not a constant
drivers/char/random.c: In function 'get_random_int':
drivers/char/random.c:2071:2: error: requested alignment is not a constant
drivers/char/random.c: In function 'get_random_long':
drivers/char/random.c:2100:2: error: requested alignment is not a constant
vim +2046 drivers/char/random.c
2040 },
2041 #endif
2042 { }
2043 };
2044 #endif /* CONFIG_SYSCTL */
2045
> 2046 static u8 random_int_secret[SIPHASH24_KEY_LEN] __aligned(SIPHASH24_ALIGNMENT);
2047
2048 int random_int_secret_init(void)
2049 {
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
On 14.12.2016 13:46, Jason A. Donenfeld wrote:
> Hi David,
>
> On Wed, Dec 14, 2016 at 10:56 AM, David Laight <[email protected]> wrote:
>> ...
>>> +u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
>> ...
>>> + u64 k0 = get_unaligned_le64(key);
>>> + u64 k1 = get_unaligned_le64(key + sizeof(u64));
>> ...
>>> + m = get_unaligned_le64(data);
>>
>> All these unaligned accesses are going to get expensive on architectures
>> like sparc64.
>
> Yes, the unaligned accesses aren't pretty. Since in pretty much all
> use cases thus far, the data can easily be made aligned, perhaps it
> makes sense to create siphash24() and siphash24_unaligned(). Any
> thoughts on doing something like that?
I fear that the alignment requirement will be a source of bugs on 32 bit
machines, where you cannot even simply take a well aligned struct on a
stack and put it into the normal siphash(aligned) function without
adding alignment annotations everywhere. Even blocks returned from
kmalloc on 32 bit are not aligned to 64 bit.
Can we do this a runtime check and just have one function (siphash)
dealing with that?
Bye,
Hannes
Hey Tom,
On Wed, Dec 14, 2016 at 10:35 PM, Tom Herbert <[email protected]> wrote:
> Those look good, although I would probably just do 1,2,3 words and
> then have a function that takes n words like jhash. Might want to call
> these dword to distinguish from 32 bit words in jhash.
So actually jhash_Nwords makes no sense, since it takes dwords
(32-bits) not words (16-bits). The siphash analog should be called
siphash24_Nqwords.
I think what I'll do is change what I already have to:
siphash24_1qword
siphash24_2qword
siphash24_3qword
siphash24_4qword
And then add some static inline helpers to assist with smaller u32s
like ipv4 addresses called:
siphash24_2dword
siphash24_4dword
siphash24_6dword
siphash24_8dword
While we're having something new, might as well call it the right thing.
> Also, what is the significance of "24" in the function and constant
> names? Can we just drop that and call this siphash?
SipHash is actually a family of PRFs, differentiated by the number of
SIPROUNDs after each 64-bit input is processed and the number of
SIPROUNDs at the very end of the function. The best trade-off of speed
and security for kernel usage is 2 rounds after each 64-bit input and
4 rounds at the end of the function. This doesn't fall to any known
cryptanalysis and it's very fast.
On Wed, Dec 14, 2016 at 2:56 PM, Jason A. Donenfeld <[email protected]> wrote:
> Hey Tom,
>
> On Wed, Dec 14, 2016 at 10:35 PM, Tom Herbert <[email protected]> wrote:
>> Those look good, although I would probably just do 1,2,3 words and
>> then have a function that takes n words like jhash. Might want to call
>> these dword to distinguish from 32 bit words in jhash.
>
> So actually jhash_Nwords makes no sense, since it takes dwords
> (32-bits) not words (16-bits). The siphash analog should be called
> siphash24_Nqwords.
>
Yeah, that's a "bug" with jhash function names.
> I think what I'll do is change what I already have to:
> siphash24_1qword
> siphash24_2qword
> siphash24_3qword
> siphash24_4qword
>
> And then add some static inline helpers to assist with smaller u32s
> like ipv4 addresses called:
>
> siphash24_2dword
> siphash24_4dword
> siphash24_6dword
> siphash24_8dword
>
> While we're having something new, might as well call it the right thing.
>
I'm confused, doesn't 2dword == 1qword? Anyway, I think the qword
functions are good enough. If someone needs to hash over some odd
length they can either put them in a structure padded to 64 bits or
call the hash function that takes a byte length.
>
>> Also, what is the significance of "24" in the function and constant
>> names? Can we just drop that and call this siphash?
>
> SipHash is actually a family of PRFs, differentiated by the number of
> SIPROUNDs after each 64-bit input is processed and the number of
> SIPROUNDs at the very end of the function. The best trade-off of speed
> and security for kernel usage is 2 rounds after each 64-bit input and
> 4 rounds at the end of the function. This doesn't fall to any known
> cryptanalysis and it's very fast.
I'd still drop the "24" unless you really think we're going to have
multiple variants coming into the kernel.
Tom
Hey Tom,
On Thu, Dec 15, 2016 at 12:14 AM, Tom Herbert <[email protected]> wrote:
> I'm confused, doesn't 2dword == 1qword? Anyway, I think the qword
> functions are good enough. If someone needs to hash over some odd
> length they can either put them in a structure padded to 64 bits or
> call the hash function that takes a byte length.
Yes. Here's an example:
static inline u64 siphash24_2dwords(const u32 a, const u32 b, const u8
key[SIPHASH24_KEY_LEN])
{
return siphash24_1qword(((u64)b << 32) | a, key);
}
This winds up being extremely useful and syntactically convenient in a
few places. Check out my git branch in about 10 minutes or wait for v4
to be posted tomorrow; these are nice helpers.
> I'd still drop the "24" unless you really think we're going to have
> multiple variants coming into the kernel.
Okay. I don't have a problem with this, unless anybody has some reason
to the contrary.
Jason
Hi Hannes,
On Wed, Dec 14, 2016 at 11:03 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> I fear that the alignment requirement will be a source of bugs on 32 bit
> machines, where you cannot even simply take a well aligned struct on a
> stack and put it into the normal siphash(aligned) function without
> adding alignment annotations everywhere. Even blocks returned from
> kmalloc on 32 bit are not aligned to 64 bit.
That's what the "__aligned(SIPHASH24_ALIGNMENT)" attribute is for. The
aligned siphash function will be for structs explicitly made for
siphash consumption. For everything else there's siphash_unaligned.
> Can we do this a runtime check and just have one function (siphash)
> dealing with that?
Seems like the runtime branching on the aligned function would be bad
for performance, when we likely know at compile time if it's going to
be aligned or not. I suppose we could add that check just to the
unaligned version, and rename it to "maybe_unaligned"? Is this what
you have in mind?
Jason
On Wed, Dec 14, 2016 at 2:56 PM, Jason A. Donenfeld <[email protected]> wrote:
>
> So actually jhash_Nwords makes no sense, since it takes dwords
> (32-bits) not words (16-bits). The siphash analog should be called
> siphash24_Nqwords.
No. The bug is talking about "words" in the first place.
Depending on your background, a "word" can be generally be either 16
bits or 32 bits (or, in some cases, 18 bits).
In theory, a 64-bit entity can be a "word" too, but pretty much nobody
uses that. Even architectures that started out with a 64-bit register
size and never had any smaller historical baggage (eg alpha) tend to
call 32-bit entities "words".
So 16 bits can be a word, but some people/architectures will call it a
"half-word".
To make matters even more confusing, a "quadword" is generally always
64 bits, regardless of the size of "word".
So please try to avoid the use of "word" entirely. It's too ambiguous,
and it's not even helpful as a "size of the native register". It's
almost purely random.
For the kernel, we tend use
- uX for types that have specific sizes (X being the number of bits)
- "[unsigned] long" for native register size
But never "word".
Linus
Hey Linus,
On Thu, Dec 15, 2016 at 12:30 AM, Linus Torvalds
<[email protected]> wrote:
> No. The bug is talking about "words" in the first place.
>
> Depending on your background, a "word" can be generally be either 16
> bits or 32 bits (or, in some cases, 18 bits).
>
> In theory, a 64-bit entity can be a "word" too, but pretty much nobody
> uses that. Even architectures that started out with a 64-bit register
> size and never had any smaller historical baggage (eg alpha) tend to
> call 32-bit entities "words".
>
> So 16 bits can be a word, but some people/architectures will call it a
> "half-word".
>
> To make matters even more confusing, a "quadword" is generally always
> 64 bits, regardless of the size of "word".
>
> So please try to avoid the use of "word" entirely. It's too ambiguous,
> and it's not even helpful as a "size of the native register". It's
> almost purely random.
>
> For the kernel, we tend use
>
> - uX for types that have specific sizes (X being the number of bits)
>
> - "[unsigned] long" for native register size
>
> But never "word".
The voice of reason. Have a desired name for this function family?
siphash_3u64s
siphash_3u64
siphash_three_u64
siphash_3sixityfourbitintegers
Or does your reasonable dislike of "word" still allow for the use of
dword and qword, so that the current function names of:
siphash_3qwords
siphash_6dwords
are okay?
Jason
On Wed, Dec 14, 2016 at 3:34 PM, Jason A. Donenfeld <[email protected]> wrote:
>
> Or does your reasonable dislike of "word" still allow for the use of
> dword and qword, so that the current function names of:
dword really is confusing to people.
If you have a MIPS background, it means 64 bits. While to people with
Windows programming backgrounds it means 32 bits.
Please try to avoid using it.
As mentioned, I think almost everybody agrees on the "q" part being 64
bits, but that may just be me not having seen it in any other context.
And before anybody points it out - yes, we already have lots of uses
of "dword" in various places. But they tend to be mostly
hardware-specific - either architectures or drivers.
So I'd _prefer_ to try to keep "word" and "dword" away from generic
helper routines. But it's not like anything is really black and white.
Linus
SipHash is a 64-bit keyed hash function that is actually a
cryptographically secure PRF, like HMAC. Except SipHash is super fast,
and is meant to be used as a hashtable keyed lookup function.
There are a variety of attacks known as "hashtable poisoning" in which an
attacker forms some data such that the hash of that data will be the
same, and then preceeds to fill up all entries of a hashbucket. This is
a realistic and well-known denial-of-service vector.
Linux developers already seem to be aware that this is an issue, and
various places that use hash tables in, say, a network context, use a
non-cryptographically secure function (usually jhash) and then try to
twiddle with the key on a time basis (or in many cases just do nothing
and hope that nobody notices). While this is an admirable attempt at
solving the problem, it doesn't actually fix it. SipHash fixes it.
(It fixes it in such a sound way that you could even build a stream
cipher out of SipHash that would resist the modern cryptanalysis.)
There are a modicum of places in the kernel that are vulnerable to
hashtable poisoning attacks, either via userspace vectors or network
vectors, and there's not a reliable mechanism inside the kernel at the
moment to fix it. The first step toward fixing these issues is actually
getting a secure primitive into the kernel for developers to use. Then
we can, bit by bit, port things over to it as deemed appropriate.
Secondly, a few places are using MD5 for creating secure sequence
numbers, port numbers, or fast random numbers. Siphash is a faster, more
fitting, and more secure replacement for MD5 in those situations.
Dozens of languages are already using this internally for their hash
tables. Some of the BSDs already use this in their kernels. SipHash is
a widely known high-speed solution to a widely known problem, and it's
time we catch-up.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Jean-Philippe Aumasson <[email protected]>
Cc: Daniel J. Bernstein <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Eric Biggers <[email protected]>
Cc: David Laight <[email protected]>
---
Changes from v3->v4:
- Renamed from siphash24 to siphash.
- Using macros instead of enums for old gcc.
- Keys must now always be aligned, even for the unaligned data
one, since generally these keys are just long term secrets
which are easy to ensure are aligned anyway.
include/linux/siphash.h | 30 ++++++++++
lib/Kconfig.debug | 6 +-
lib/Makefile | 5 +-
lib/siphash.c | 153 ++++++++++++++++++++++++++++++++++++++++++++++++
lib/test_siphash.c | 84 ++++++++++++++++++++++++++
5 files changed, 273 insertions(+), 5 deletions(-)
create mode 100644 include/linux/siphash.h
create mode 100644 lib/siphash.c
create mode 100644 lib/test_siphash.c
diff --git a/include/linux/siphash.h b/include/linux/siphash.h
new file mode 100644
index 000000000000..d0bcca7b992b
--- /dev/null
+++ b/include/linux/siphash.h
@@ -0,0 +1,30 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>. All Rights Reserved.
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ *
+ * This implementation is specifically for SipHash2-4.
+ */
+
+#ifndef _LINUX_SIPHASH_H
+#define _LINUX_SIPHASH_H
+
+#include <linux/types.h>
+
+#define SIPHASH_KEY_LEN 16
+#define SIPHASH_ALIGNMENT 8
+
+u64 siphash(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN]);
+
+#ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+static inline u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
+{
+ return siphash(data, len, key);
+}
+#else
+u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN]);
+#endif
+
+#endif /* _LINUX_SIPHASH_H */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index e6327d102184..32bbf689fc46 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1843,9 +1843,9 @@ config TEST_HASH
tristate "Perform selftest on hash functions"
default n
help
- Enable this option to test the kernel's integer (<linux/hash,h>)
- and string (<linux/stringhash.h>) hash functions on boot
- (or module load).
+ Enable this option to test the kernel's integer (<linux/hash.h>),
+ string (<linux/stringhash.h>), and siphash (<linux/siphash.h>)
+ hash functions on boot (or module load).
This is intended to help people writing architecture-specific
optimized versions. If unsure, say N.
diff --git a/lib/Makefile b/lib/Makefile
index 50144a3aeebd..71d398b04a74 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -22,7 +22,8 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
sha1.o chacha20.o md5.o irq_regs.o argv_split.o \
flex_proportions.o ratelimit.o show_mem.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
- earlycpio.o seq_buf.o nmi_backtrace.o nodemask.o win_minmax.o
+ earlycpio.o seq_buf.o siphash.o \
+ nmi_backtrace.o nodemask.o win_minmax.o
lib-$(CONFIG_MMU) += ioremap.o
lib-$(CONFIG_SMP) += cpumask.o
@@ -44,7 +45,7 @@ obj-$(CONFIG_TEST_HEXDUMP) += test_hexdump.o
obj-y += kstrtox.o
obj-$(CONFIG_TEST_BPF) += test_bpf.o
obj-$(CONFIG_TEST_FIRMWARE) += test_firmware.o
-obj-$(CONFIG_TEST_HASH) += test_hash.o
+obj-$(CONFIG_TEST_HASH) += test_hash.o test_siphash.o
obj-$(CONFIG_TEST_KASAN) += test_kasan.o
obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
obj-$(CONFIG_TEST_LKM) += test_module.o
diff --git a/lib/siphash.c b/lib/siphash.c
new file mode 100644
index 000000000000..b500231f61cd
--- /dev/null
+++ b/lib/siphash.c
@@ -0,0 +1,153 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>. All Rights Reserved.
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ *
+ * This implementation is specifically for SipHash2-4.
+ */
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <asm/unaligned.h>
+
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+#include <linux/dcache.h>
+#include <asm/word-at-a-time.h>
+#endif
+
+static inline u16 le16_to_cpuvp(const void *p)
+{
+ return le16_to_cpup(p);
+}
+static inline u32 le32_to_cpuvp(const void *p)
+{
+ return le32_to_cpup(p);
+}
+static inline u64 le64_to_cpuvp(const void *p)
+{
+ return le64_to_cpup(p);
+}
+
+#define SIPROUND \
+ do { \
+ v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
+ v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
+ v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
+ v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
+ } while(0)
+
+/**
+ * siphash - compute 64-bit siphash PRF value
+ * @data: buffer to hash, must be aligned to SIPHASH_ALIGNMENT
+ * @size: size of @data
+ * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
+ */
+u64 siphash(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
+{
+ u64 v0 = 0x736f6d6570736575ULL;
+ u64 v1 = 0x646f72616e646f6dULL;
+ u64 v2 = 0x6c7967656e657261ULL;
+ u64 v3 = 0x7465646279746573ULL;
+ u64 b = ((u64)len) << 56;
+ u64 k0 = le64_to_cpuvp(key);
+ u64 k1 = le64_to_cpuvp(key + sizeof(u64));
+ u64 m;
+ const u8 *end = data + len - (len % sizeof(u64));
+ const u8 left = len & (sizeof(u64) - 1);
+ v3 ^= k1;
+ v2 ^= k0;
+ v1 ^= k1;
+ v0 ^= k0;
+ for (; data != end; data += sizeof(u64)) {
+ m = le64_to_cpuvp(data);
+ v3 ^= m;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= m;
+ }
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+ if (left)
+ b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
+#else
+ switch (left) {
+ case 7: b |= ((u64)data[6]) << 48;
+ case 6: b |= ((u64)data[5]) << 40;
+ case 5: b |= ((u64)data[4]) << 32;
+ case 4: b |= le32_to_cpuvp(data); break;
+ case 3: b |= ((u64)data[2]) << 16;
+ case 2: b |= le16_to_cpuvp(data); break;
+ case 1: b |= data[0];
+ }
+#endif
+ v3 ^= b;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= b;
+ v2 ^= 0xff;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ return (v0 ^ v1) ^ (v2 ^ v3);
+}
+EXPORT_SYMBOL(siphash);
+
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+/**
+ * siphash - compute 64-bit siphash PRF value, without alignment requirements
+ * @data: buffer to hash
+ * @size: size of @data
+ * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
+ */
+u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
+{
+ u64 v0 = 0x736f6d6570736575ULL;
+ u64 v1 = 0x646f72616e646f6dULL;
+ u64 v2 = 0x6c7967656e657261ULL;
+ u64 v3 = 0x7465646279746573ULL;
+ u64 b = ((u64)len) << 56;
+ u64 k0 = le64_to_cpuvp(key);
+ u64 k1 = le64_to_cpuvp(key + sizeof(u64));
+ u64 m;
+ const u8 *end = data + len - (len % sizeof(u64));
+ const u8 left = len & (sizeof(u64) - 1);
+ v3 ^= k1;
+ v2 ^= k0;
+ v1 ^= k1;
+ v0 ^= k0;
+ for (; data != end; data += sizeof(u64)) {
+ m = get_unaligned_le64(data);
+ v3 ^= m;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= m;
+ }
+#if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
+ if (left)
+ b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
+#else
+ switch (left) {
+ case 7: b |= ((u64)data[6]) << 48;
+ case 6: b |= ((u64)data[5]) << 40;
+ case 5: b |= ((u64)data[4]) << 32;
+ case 4: b |= get_unaligned_le32(data); break;
+ case 3: b |= ((u64)data[2]) << 16;
+ case 2: b |= get_unaligned_le16(data); break;
+ case 1: b |= data[0];
+ }
+#endif
+ v3 ^= b;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= b;
+ v2 ^= 0xff;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ SIPROUND;
+ return (v0 ^ v1) ^ (v2 ^ v3);
+}
+EXPORT_SYMBOL(siphash24_unaligned);
+#endif
diff --git a/lib/test_siphash.c b/lib/test_siphash.c
new file mode 100644
index 000000000000..444725c7834f
--- /dev/null
+++ b/lib/test_siphash.c
@@ -0,0 +1,84 @@
+/* Test cases for siphash.c
+ *
+ * Copyright (C) 2016 Jason A. Donenfeld <[email protected]>. All Rights Reserved.
+ *
+ * This file is provided under a dual BSD/GPLv2 license.
+ *
+ * SipHash: a fast short-input PRF
+ * https://131002.net/siphash/
+ *
+ * This implementation is specifically for SipHash2-4.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/siphash.h>
+#include <linux/kernel.h>
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+
+/* Test vectors taken from official reference source available at:
+ * https://131002.net/siphash/siphash24.c
+ */
+static const u64 test_vectors[64] = {
+ 0x726fdb47dd0e0e31ULL, 0x74f839c593dc67fdULL, 0x0d6c8009d9a94f5aULL,
+ 0x85676696d7fb7e2dULL, 0xcf2794e0277187b7ULL, 0x18765564cd99a68dULL,
+ 0xcbc9466e58fee3ceULL, 0xab0200f58b01d137ULL, 0x93f5f5799a932462ULL,
+ 0x9e0082df0ba9e4b0ULL, 0x7a5dbbc594ddb9f3ULL, 0xf4b32f46226bada7ULL,
+ 0x751e8fbc860ee5fbULL, 0x14ea5627c0843d90ULL, 0xf723ca908e7af2eeULL,
+ 0xa129ca6149be45e5ULL, 0x3f2acc7f57c29bdbULL, 0x699ae9f52cbe4794ULL,
+ 0x4bc1b3f0968dd39cULL, 0xbb6dc91da77961bdULL, 0xbed65cf21aa2ee98ULL,
+ 0xd0f2cbb02e3b67c7ULL, 0x93536795e3a33e88ULL, 0xa80c038ccd5ccec8ULL,
+ 0xb8ad50c6f649af94ULL, 0xbce192de8a85b8eaULL, 0x17d835b85bbb15f3ULL,
+ 0x2f2e6163076bcfadULL, 0xde4daaaca71dc9a5ULL, 0xa6a2506687956571ULL,
+ 0xad87a3535c49ef28ULL, 0x32d892fad841c342ULL, 0x7127512f72f27cceULL,
+ 0xa7f32346f95978e3ULL, 0x12e0b01abb051238ULL, 0x15e034d40fa197aeULL,
+ 0x314dffbe0815a3b4ULL, 0x027990f029623981ULL, 0xcadcd4e59ef40c4dULL,
+ 0x9abfd8766a33735cULL, 0x0e3ea96b5304a7d0ULL, 0xad0c42d6fc585992ULL,
+ 0x187306c89bc215a9ULL, 0xd4a60abcf3792b95ULL, 0xf935451de4f21df2ULL,
+ 0xa9538f0419755787ULL, 0xdb9acddff56ca510ULL, 0xd06c98cd5c0975ebULL,
+ 0xe612a3cb9ecba951ULL, 0xc766e62cfcadaf96ULL, 0xee64435a9752fe72ULL,
+ 0xa192d576b245165aULL, 0x0a8787bf8ecb74b2ULL, 0x81b3e73d20b49b6fULL,
+ 0x7fa8220ba3b2eceaULL, 0x245731c13ca42499ULL, 0xb78dbfaf3a8d83bdULL,
+ 0xea1ad565322a1a0bULL, 0x60e61c23a3795013ULL, 0x6606d7e446282b93ULL,
+ 0x6ca4ecb15c5f91e1ULL, 0x9f626da15c9625f3ULL, 0xe51b38608ef25f57ULL,
+ 0x958a324ceb064572ULL
+};
+
+static int __init siphash_test_init(void)
+{
+ u8 in[64] __aligned(SIPHASH_ALIGNMENT);
+ u8 k[16] __aligned(SIPHASH_ALIGNMENT);
+ u8 in_unaligned[65];
+ u8 i;
+ int ret = 0;
+
+ for (i = 0; i < 16; ++i)
+ k[i] = i;
+ for (i = 0; i < 64; ++i) {
+ in[i] = i;
+ in_unaligned[i + 1] = i;
+ if (siphash(in, i, k) != test_vectors[i]) {
+ pr_info("self-test aligned %u: FAIL\n", i + 1);
+ ret = -EINVAL;
+ }
+ if (siphash_unaligned(in_unaligned + 1, i, k) != test_vectors[i]) {
+ pr_info("self-test unaligned %u: FAIL\n", i + 1);
+ ret = -EINVAL;
+ }
+ }
+ if (!ret)
+ pr_info("self-tests: pass\n");
+ return ret;
+}
+
+static void __exit siphash_test_exit(void)
+{
+}
+
+module_init(siphash_test_init);
+module_exit(siphash_test_exit);
+
+MODULE_AUTHOR("Jason A. Donenfeld <[email protected]>");
+MODULE_LICENSE("Dual BSD/GPL");
--
2.11.0
These restore parity with the jhash interface by providing high
performance helpers for common input sizes.
Linus doesn't like the use of "qword" and "dword", but I haven't been
able to come up with another name for these that fits as well.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Tom Herbert <[email protected]>
---
Changes from v2->v4:
- Rather than just wrapping siphash(), we actually implement the
fully optimized and manually unrolled version, so that lengths
don't need to be checked and loops don't need to branch.
- We now provide both 32-bit and 64-bit versions, both of which
are quite useful for different circumstances.
include/linux/siphash.h | 31 ++++++++++
lib/siphash.c | 161 ++++++++++++++++++++++++++++++++++++------------
lib/test_siphash.c | 18 ++++++
3 files changed, 170 insertions(+), 40 deletions(-)
diff --git a/include/linux/siphash.h b/include/linux/siphash.h
index d0bcca7b992b..6e7c2a421bd9 100644
--- a/include/linux/siphash.h
+++ b/include/linux/siphash.h
@@ -27,4 +27,35 @@ static inline u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIP
u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN]);
#endif
+u64 siphash_1qword(const u64 a, const u8 key[SIPHASH_KEY_LEN]);
+u64 siphash_2qwords(const u64 a, const u64 b, const u8 key[SIPHASH_KEY_LEN]);
+u64 siphash_3qwords(const u64 a, const u64 b, const u64 c, const u8 key[SIPHASH_KEY_LEN]);
+u64 siphash_4qwords(const u64 a, const u64 b, const u64 c, const u64 d, const u8 key[SIPHASH_KEY_LEN]);
+
+static inline u64 siphash_2dwords(const u32 a, const u32 b, const u8 key[SIPHASH_KEY_LEN])
+{
+ return siphash_1qword((u64)b << 32 | a, key);
+}
+
+static inline u64 siphash_4dwords(const u32 a, const u32 b, const u32 c, const u32 d,
+ const u8 key[SIPHASH_KEY_LEN])
+{
+ return siphash_2qwords((u64)b << 32 | a, (u64)d << 32 | c, key);
+}
+
+static inline u64 siphash_6dwords(const u32 a, const u32 b, const u32 c, const u32 d,
+ const u32 e, const u32 f, const u8 key[SIPHASH_KEY_LEN])
+{
+ return siphash_3qwords((u64)b << 32 | a, (u64)d << 32 | c, (u64)f << 32 | e,
+ key);
+}
+
+static inline u64 siphash_8dwords(const u32 a, const u32 b, const u32 c, const u32 d,
+ const u32 e, const u32 f, const u32 g, const u32 h,
+ const u8 key[SIPHASH_KEY_LEN])
+{
+ return siphash_4qwords((u64)b << 32 | a, (u64)d << 32 | c, (u64)f << 32 | e,
+ (u64)h << 32 | g, key);
+}
+
#endif /* _LINUX_SIPHASH_H */
diff --git a/lib/siphash.c b/lib/siphash.c
index b500231f61cd..c13d2b2bb76e 100644
--- a/lib/siphash.c
+++ b/lib/siphash.c
@@ -38,6 +38,31 @@ static inline u64 le64_to_cpuvp(const void *p)
v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
} while(0)
+#define PREAMBLE(len) \
+ u64 v0 = 0x736f6d6570736575ULL; \
+ u64 v1 = 0x646f72616e646f6dULL; \
+ u64 v2 = 0x6c7967656e657261ULL; \
+ u64 v3 = 0x7465646279746573ULL; \
+ u64 b = ((u64)len) << 56; \
+ u64 k0 = le64_to_cpuvp(key); \
+ u64 k1 = le64_to_cpuvp(key + sizeof(u64)); \
+ v3 ^= k1; \
+ v2 ^= k0; \
+ v1 ^= k1; \
+ v0 ^= k0;
+
+#define POSTAMBLE \
+ v3 ^= b; \
+ SIPROUND; \
+ SIPROUND; \
+ v0 ^= b; \
+ v2 ^= 0xff; \
+ SIPROUND; \
+ SIPROUND; \
+ SIPROUND; \
+ SIPROUND; \
+ return (v0 ^ v1) ^ (v2 ^ v3);
+
/**
* siphash - compute 64-bit siphash PRF value
* @data: buffer to hash, must be aligned to SIPHASH_ALIGNMENT
@@ -46,20 +71,10 @@ static inline u64 le64_to_cpuvp(const void *p)
*/
u64 siphash(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
{
- u64 v0 = 0x736f6d6570736575ULL;
- u64 v1 = 0x646f72616e646f6dULL;
- u64 v2 = 0x6c7967656e657261ULL;
- u64 v3 = 0x7465646279746573ULL;
- u64 b = ((u64)len) << 56;
- u64 k0 = le64_to_cpuvp(key);
- u64 k1 = le64_to_cpuvp(key + sizeof(u64));
- u64 m;
const u8 *end = data + len - (len % sizeof(u64));
const u8 left = len & (sizeof(u64) - 1);
- v3 ^= k1;
- v2 ^= k0;
- v1 ^= k1;
- v0 ^= k0;
+ u64 m;
+ PREAMBLE(len)
for (; data != end; data += sizeof(u64)) {
m = le64_to_cpuvp(data);
v3 ^= m;
@@ -81,16 +96,7 @@ u64 siphash(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
case 1: b |= data[0];
}
#endif
- v3 ^= b;
- SIPROUND;
- SIPROUND;
- v0 ^= b;
- v2 ^= 0xff;
- SIPROUND;
- SIPROUND;
- SIPROUND;
- SIPROUND;
- return (v0 ^ v1) ^ (v2 ^ v3);
+ POSTAMBLE
}
EXPORT_SYMBOL(siphash);
@@ -103,20 +109,10 @@ EXPORT_SYMBOL(siphash);
*/
u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
{
- u64 v0 = 0x736f6d6570736575ULL;
- u64 v1 = 0x646f72616e646f6dULL;
- u64 v2 = 0x6c7967656e657261ULL;
- u64 v3 = 0x7465646279746573ULL;
- u64 b = ((u64)len) << 56;
- u64 k0 = le64_to_cpuvp(key);
- u64 k1 = le64_to_cpuvp(key + sizeof(u64));
- u64 m;
const u8 *end = data + len - (len % sizeof(u64));
const u8 left = len & (sizeof(u64) - 1);
- v3 ^= k1;
- v2 ^= k0;
- v1 ^= k1;
- v0 ^= k0;
+ u64 m;
+ PREAMBLE(len)
for (; data != end; data += sizeof(u64)) {
m = get_unaligned_le64(data);
v3 ^= m;
@@ -138,16 +134,101 @@ u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
case 1: b |= data[0];
}
#endif
- v3 ^= b;
+ POSTAMBLE
+}
+EXPORT_SYMBOL(siphash_unaligned);
+#endif
+
+/**
+ * siphash_1qword - compute 64-bit siphash PRF value of 1 quad-word
+ * @first: first quadword
+ * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
+ */
+u64 siphash_1qword(const u64 first, const u8 key[SIPHASH_KEY_LEN])
+{
+ PREAMBLE(8)
+ v3 ^= first;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= first;
+ POSTAMBLE
+}
+EXPORT_SYMBOL(siphash_1qword);
+
+/**
+ * siphash_2qwords - compute 64-bit siphash PRF value of 2 quad-words
+ * @first: first quadword
+ * @second: second quadword
+ * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
+ */
+u64 siphash_2qwords(const u64 first, const u64 second, const u8 key[SIPHASH_KEY_LEN])
+{
+ PREAMBLE(16)
+ v3 ^= first;
SIPROUND;
SIPROUND;
- v0 ^= b;
- v2 ^= 0xff;
+ v0 ^= first;
+ v3 ^= second;
SIPROUND;
SIPROUND;
+ v0 ^= second;
+ POSTAMBLE
+}
+EXPORT_SYMBOL(siphash_2qwords);
+
+/**
+ * siphash_3qwords - compute 64-bit siphash PRF value of 3 quad-words
+ * @first: first quadword
+ * @second: second quadword
+ * @third: third quadword
+ * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
+ */
+u64 siphash_3qwords(const u64 first, const u64 second, const u64 third, const u8 key[SIPHASH_KEY_LEN])
+{
+ PREAMBLE(24)
+ v3 ^= first;
SIPROUND;
SIPROUND;
- return (v0 ^ v1) ^ (v2 ^ v3);
+ v0 ^= first;
+ v3 ^= second;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= second;
+ v3 ^= third;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= third;
+ POSTAMBLE
}
-EXPORT_SYMBOL(siphash24_unaligned);
-#endif
+EXPORT_SYMBOL(siphash_3qwords);
+
+/**
+ * siphash_4qwords - compute 64-bit siphash PRF value of 4 quad-words
+ * @first: first quadword
+ * @second: second quadword
+ * @third: third quadword
+ * @forth: forth quadword
+ * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
+ */
+u64 siphash_4qwords(const u64 first, const u64 second, const u64 third, const u64 forth, const u8 key[SIPHASH_KEY_LEN])
+{
+ PREAMBLE(32)
+ v3 ^= first;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= first;
+ v3 ^= second;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= second;
+ v3 ^= third;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= third;
+ v3 ^= forth;
+ SIPROUND;
+ SIPROUND;
+ v0 ^= forth;
+ POSTAMBLE
+}
+EXPORT_SYMBOL(siphash_4qwords);
diff --git a/lib/test_siphash.c b/lib/test_siphash.c
index 444725c7834f..9925a325af35 100644
--- a/lib/test_siphash.c
+++ b/lib/test_siphash.c
@@ -68,6 +68,24 @@ static int __init siphash_test_init(void)
ret = -EINVAL;
}
}
+ if (siphash_1qword(0x0706050403020100ULL, k) != test_vectors[8]) {
+ pr_info("self-test 1qword: FAIL\n");
+ ret = -EINVAL;
+ }
+ if (siphash_2qwords(0x0706050403020100ULL, 0x0f0e0d0c0b0a0908ULL, k) != test_vectors[16]) {
+ pr_info("self-test 2qwords: FAIL\n");
+ ret = -EINVAL;
+ }
+ if (siphash_3qwords(0x0706050403020100ULL, 0x0f0e0d0c0b0a0908ULL,
+ 0x1716151413121110ULL, k) != test_vectors[24]) {
+ pr_info("self-test 3qwords: FAIL\n");
+ ret = -EINVAL;
+ }
+ if (siphash_4qwords(0x0706050403020100ULL, 0x0f0e0d0c0b0a0908ULL,
+ 0x1716151413121110ULL, 0x1f1e1d1c1b1a1918ULL, k) != test_vectors[32]) {
+ pr_info("self-test 4qwords: FAIL\n");
+ ret = -EINVAL;
+ }
if (!ret)
pr_info("self-tests: pass\n");
return ret;
--
2.11.0
This duplicates the current algorithm for get_random_int/long, but uses
siphash instead. This comes with several benefits. It's certainly
faster and more cryptographically secure than MD5. This patch also
separates hashed fields into three values instead of one, in order to
increase diffusion.
The previous MD5 algorithm used a per-cpu MD5 state, which caused
successive calls to the function to chain upon each other. While it's
not entirely clear that this kind of chaining is absolutely necessary
when using a secure PRF like siphash, it can't hurt, and the timing of
the call chain does add a degree of natural entropy. So, in keeping with
this design, instead of the massive per-cpu 64-byte MD5 state, there is
instead a per-cpu previously returned value for chaining.
The speed benefits are substantial:
| siphash | md5 | speedup |
------------------------------
get_random_long | 137130 | 415983 | 3.03x |
get_random_int | 86384 | 343323 | 3.97x |
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Jean-Philippe Aumasson <[email protected]>
Cc: Ted Tso <[email protected]>
---
Changes from v3->v4:
- Speedups by using the 3qwords function.
drivers/char/random.c | 30 +++++++++++-------------------
1 file changed, 11 insertions(+), 19 deletions(-)
diff --git a/drivers/char/random.c b/drivers/char/random.c
index d6876d506220..8e1d1cfface6 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -262,6 +262,7 @@
#include <linux/syscalls.h>
#include <linux/completion.h>
#include <linux/uuid.h>
+#include <linux/siphash.h>
#include <crypto/chacha20.h>
#include <asm/processor.h>
@@ -2042,7 +2043,7 @@ struct ctl_table random_table[] = {
};
#endif /* CONFIG_SYSCTL */
-static u32 random_int_secret[MD5_MESSAGE_BYTES / 4] ____cacheline_aligned;
+static u8 random_int_secret[SIPHASH_KEY_LEN] __aligned(SIPHASH_ALIGNMENT);
int random_int_secret_init(void)
{
@@ -2050,8 +2051,7 @@ int random_int_secret_init(void)
return 0;
}
-static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash)
- __aligned(sizeof(unsigned long));
+static DEFINE_PER_CPU(u64, get_random_int_chaining);
/*
* Get a random word for internal kernel use only. Similar to urandom but
@@ -2061,19 +2061,15 @@ static DEFINE_PER_CPU(__u32 [MD5_DIGEST_WORDS], get_random_int_hash)
*/
unsigned int get_random_int(void)
{
- __u32 *hash;
unsigned int ret;
+ u64 *chaining;
if (arch_get_random_int(&ret))
return ret;
- hash = get_cpu_var(get_random_int_hash);
-
- hash[0] += current->pid + jiffies + random_get_entropy();
- md5_transform(hash, random_int_secret);
- ret = hash[0];
- put_cpu_var(get_random_int_hash);
-
+ chaining = &get_cpu_var(get_random_int_chaining);
+ ret = *chaining = siphash_3qwords(*chaining, jiffies, random_get_entropy() + current->pid, random_int_secret);
+ put_cpu_var(get_random_int_chaining);
return ret;
}
EXPORT_SYMBOL(get_random_int);
@@ -2083,19 +2079,15 @@ EXPORT_SYMBOL(get_random_int);
*/
unsigned long get_random_long(void)
{
- __u32 *hash;
unsigned long ret;
+ u64 *chaining;
if (arch_get_random_long(&ret))
return ret;
- hash = get_cpu_var(get_random_int_hash);
-
- hash[0] += current->pid + jiffies + random_get_entropy();
- md5_transform(hash, random_int_secret);
- ret = *(unsigned long *)hash;
- put_cpu_var(get_random_int_hash);
-
+ chaining = &get_cpu_var(get_random_int_chaining);
+ ret = *chaining = siphash_3qwords(*chaining, jiffies, random_get_entropy() + current->pid, random_int_secret);
+ put_cpu_var(get_random_int_chaining);
return ret;
}
EXPORT_SYMBOL(get_random_long);
--
2.11.0
This gives a clear speed and security improvement. Siphash is both
faster and is more solid crypto than the aging MD5.
Rather than manually filling MD5 buffers, for IPv6, we simply create
a layout by a simple anonymous struct, for which gcc generates
rather efficient code. For IPv4, we pass the values directly to the
short input convenience functions.
Signed-off-by: Jason A. Donenfeld <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: David Miller <[email protected]>
Cc: David Laight <[email protected]>
Cc: Tom Herbert <[email protected]>
Cc: Hannes Frederic Sowa <[email protected]>
---
Changes from v3->v4:
- For the IPv4 cases, we can now use the Ndwords helper functions,
which make the calculation simpler and faster.
- For the IPv6 cases, which still use the struct, we no longer pack
the struct and instead simply pad until the nearest 64-bit size, so
that it also avoids the slow branch for left-overs in siphash().
net/core/secure_seq.c | 133 ++++++++++++++++++++------------------------------
1 file changed, 52 insertions(+), 81 deletions(-)
diff --git a/net/core/secure_seq.c b/net/core/secure_seq.c
index 88a8e429fc3e..8fed79932ec4 100644
--- a/net/core/secure_seq.c
+++ b/net/core/secure_seq.c
@@ -1,3 +1,5 @@
+/* Copyright (C) 2016 Jason A. Donenfeld <[email protected]>. All Rights Reserved. */
+
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/cryptohash.h>
@@ -8,14 +10,14 @@
#include <linux/ktime.h>
#include <linux/string.h>
#include <linux/net.h>
-
+#include <linux/siphash.h>
#include <net/secure_seq.h>
#if IS_ENABLED(CONFIG_IPV6) || IS_ENABLED(CONFIG_INET)
+#include <linux/in6.h>
#include <net/tcp.h>
-#define NET_SECRET_SIZE (MD5_MESSAGE_BYTES / 4)
-static u32 net_secret[NET_SECRET_SIZE] ____cacheline_aligned;
+static u8 net_secret[SIPHASH_KEY_LEN] __aligned(SIPHASH_ALIGNMENT);
static __always_inline void net_secret_init(void)
{
@@ -44,44 +46,42 @@ static u32 seq_scale(u32 seq)
u32 secure_tcpv6_sequence_number(const __be32 *saddr, const __be32 *daddr,
__be16 sport, __be16 dport, u32 *tsoff)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
- u32 i;
-
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 sport;
+ __be16 dport;
+ u32 padding;
+ } __aligned(SIPHASH_ALIGNMENT) combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .sport = sport,
+ .dport = dport
+ };
+ u64 hash;
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32)daddr[i];
- secret[4] = net_secret[4] +
- (((__force u16)sport << 16) + (__force u16)dport);
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- *tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
- return seq_scale(hash[0]);
+ hash = siphash((const u8 *)&combined, sizeof(combined), net_secret);
+ *tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;
+ return seq_scale(hash);
}
EXPORT_SYMBOL(secure_tcpv6_sequence_number);
u32 secure_ipv6_port_ephemeral(const __be32 *saddr, const __be32 *daddr,
__be16 dport)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
- u32 i;
-
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 dport;
+ u16 padding1;
+ u32 padding2;
+ } __aligned(SIPHASH_ALIGNMENT) combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .dport = dport
+ };
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32) daddr[i];
- secret[4] = net_secret[4] + (__force u32)dport;
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- return hash[0];
+ return siphash((const u8 *)&combined, sizeof(combined), net_secret);
}
EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
#endif
@@ -91,33 +91,17 @@ EXPORT_SYMBOL(secure_ipv6_port_ephemeral);
u32 secure_tcp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport, u32 *tsoff)
{
- u32 hash[MD5_DIGEST_WORDS];
-
+ u64 hash;
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- *tsoff = sysctl_tcp_timestamps == 1 ? hash[1] : 0;
- return seq_scale(hash[0]);
+ hash = siphash_4dwords(saddr, daddr, sport, dport, net_secret);
+ *tsoff = sysctl_tcp_timestamps == 1 ? (hash >> 32) : 0;
+ return seq_scale(hash);
}
u32 secure_ipv4_port_ephemeral(__be32 saddr, __be32 daddr, __be16 dport)
{
- u32 hash[MD5_DIGEST_WORDS];
-
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = (__force u32)dport ^ net_secret[14];
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- return hash[0];
+ return siphash_4dwords(saddr, daddr, dport, 0, net_secret);
}
EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
#endif
@@ -126,21 +110,11 @@ EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);
u64 secure_dccp_sequence_number(__be32 saddr, __be32 daddr,
__be16 sport, __be16 dport)
{
- u32 hash[MD5_DIGEST_WORDS];
u64 seq;
-
net_secret_init();
- hash[0] = (__force u32)saddr;
- hash[1] = (__force u32)daddr;
- hash[2] = ((__force u16)sport << 16) + (__force u16)dport;
- hash[3] = net_secret[15];
-
- md5_transform(hash, net_secret);
-
- seq = hash[0] | (((u64)hash[1]) << 32);
+ seq = siphash_4dwords(saddr, daddr, sport, dport, net_secret);
seq += ktime_get_real_ns();
seq &= (1ull << 48) - 1;
-
return seq;
}
EXPORT_SYMBOL(secure_dccp_sequence_number);
@@ -149,26 +123,23 @@ EXPORT_SYMBOL(secure_dccp_sequence_number);
u64 secure_dccpv6_sequence_number(__be32 *saddr, __be32 *daddr,
__be16 sport, __be16 dport)
{
- u32 secret[MD5_MESSAGE_BYTES / 4];
- u32 hash[MD5_DIGEST_WORDS];
+ const struct {
+ struct in6_addr saddr;
+ struct in6_addr daddr;
+ __be16 sport;
+ __be16 dport;
+ u32 padding;
+ } __aligned(SIPHASH_ALIGNMENT) combined = {
+ .saddr = *(struct in6_addr *)saddr,
+ .daddr = *(struct in6_addr *)daddr,
+ .sport = sport,
+ .dport = dport
+ };
u64 seq;
- u32 i;
-
net_secret_init();
- memcpy(hash, saddr, 16);
- for (i = 0; i < 4; i++)
- secret[i] = net_secret[i] + (__force u32)daddr[i];
- secret[4] = net_secret[4] +
- (((__force u16)sport << 16) + (__force u16)dport);
- for (i = 5; i < MD5_MESSAGE_BYTES / 4; i++)
- secret[i] = net_secret[i];
-
- md5_transform(hash, secret);
-
- seq = hash[0] | (((u64)hash[1]) << 32);
+ seq = siphash((const u8 *)&combined, sizeof(combined), net_secret);
seq += ktime_get_real_ns();
seq &= (1ull << 48) - 1;
-
return seq;
}
EXPORT_SYMBOL(secure_dccpv6_sequence_number);
--
2.11.0
Hi Jason,
[auto build test ERROR on linus/master]
[also build test ERROR on v4.9 next-20161215]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Jason-A-Donenfeld/siphash-add-cryptographically-secure-hashtable-function/20161215-095213
config: ia64-allmodconfig (attached as .config)
compiler: ia64-linux-gcc (GCC) 6.2.0
reproduce:
wget https://git.kernel.org/cgit/linux/kernel/git/wfg/lkp-tests.git/plain/sbin/make.cross -O ~/bin/make.cross
chmod +x ~/bin/make.cross
# save the attached .config to linux build tree
make.cross ARCH=ia64
Note: the linux-review/Jason-A-Donenfeld/siphash-add-cryptographically-secure-hashtable-function/20161215-095213 HEAD 3e343f4316f94cded0d1384cf35957fd51dbbc28 builds fine.
It only hurts bisectibility.
All error/warnings (new ones prefixed by >>):
In file included from include/linux/linkage.h:6:0,
from include/linux/kernel.h:6,
from lib/siphash.c:12:
>> lib/siphash.c:152:15: error: 'siphash24_unaligned' undeclared here (not in a function)
EXPORT_SYMBOL(siphash24_unaligned);
^
include/linux/export.h:58:16: note: in definition of macro '___EXPORT_SYMBOL'
extern typeof(sym) sym; \
^~~
>> lib/siphash.c:152:1: note: in expansion of macro 'EXPORT_SYMBOL'
EXPORT_SYMBOL(siphash24_unaligned);
^~~~~~~~~~~~~
vim +/siphash24_unaligned +152 lib/siphash.c
6 * https://131002.net/siphash/
7 *
8 * This implementation is specifically for SipHash2-4.
9 */
10
11 #include <linux/siphash.h>
> 12 #include <linux/kernel.h>
13 #include <asm/unaligned.h>
14
15 #if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
16 #include <linux/dcache.h>
17 #include <asm/word-at-a-time.h>
18 #endif
19
20 static inline u16 le16_to_cpuvp(const void *p)
21 {
22 return le16_to_cpup(p);
23 }
24 static inline u32 le32_to_cpuvp(const void *p)
25 {
26 return le32_to_cpup(p);
27 }
28 static inline u64 le64_to_cpuvp(const void *p)
29 {
30 return le64_to_cpup(p);
31 }
32
33 #define SIPROUND \
34 do { \
35 v0 += v1; v1 = rol64(v1, 13); v1 ^= v0; v0 = rol64(v0, 32); \
36 v2 += v3; v3 = rol64(v3, 16); v3 ^= v2; \
37 v0 += v3; v3 = rol64(v3, 21); v3 ^= v0; \
38 v2 += v1; v1 = rol64(v1, 17); v1 ^= v2; v2 = rol64(v2, 32); \
39 } while(0)
40
41 /**
42 * siphash - compute 64-bit siphash PRF value
43 * @data: buffer to hash, must be aligned to SIPHASH_ALIGNMENT
44 * @size: size of @data
45 * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
46 */
47 u64 siphash(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
48 {
49 u64 v0 = 0x736f6d6570736575ULL;
50 u64 v1 = 0x646f72616e646f6dULL;
51 u64 v2 = 0x6c7967656e657261ULL;
52 u64 v3 = 0x7465646279746573ULL;
53 u64 b = ((u64)len) << 56;
54 u64 k0 = le64_to_cpuvp(key);
55 u64 k1 = le64_to_cpuvp(key + sizeof(u64));
56 u64 m;
57 const u8 *end = data + len - (len % sizeof(u64));
58 const u8 left = len & (sizeof(u64) - 1);
59 v3 ^= k1;
60 v2 ^= k0;
61 v1 ^= k1;
62 v0 ^= k0;
63 for (; data != end; data += sizeof(u64)) {
64 m = le64_to_cpuvp(data);
65 v3 ^= m;
66 SIPROUND;
67 SIPROUND;
68 v0 ^= m;
69 }
70 #if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
71 if (left)
72 b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
73 #else
74 switch (left) {
75 case 7: b |= ((u64)data[6]) << 48;
76 case 6: b |= ((u64)data[5]) << 40;
77 case 5: b |= ((u64)data[4]) << 32;
78 case 4: b |= le32_to_cpuvp(data); break;
79 case 3: b |= ((u64)data[2]) << 16;
80 case 2: b |= le16_to_cpuvp(data); break;
81 case 1: b |= data[0];
82 }
83 #endif
84 v3 ^= b;
85 SIPROUND;
86 SIPROUND;
87 v0 ^= b;
88 v2 ^= 0xff;
89 SIPROUND;
90 SIPROUND;
91 SIPROUND;
92 SIPROUND;
93 return (v0 ^ v1) ^ (v2 ^ v3);
94 }
95 EXPORT_SYMBOL(siphash);
96
97 #ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
98 /**
99 * siphash - compute 64-bit siphash PRF value, without alignment requirements
100 * @data: buffer to hash
101 * @size: size of @data
102 * @key: key buffer of size SIPHASH_KEY_LEN, must be aligned to SIPHASH_ALIGNMENT
103 */
104 u64 siphash_unaligned(const u8 *data, size_t len, const u8 key[SIPHASH_KEY_LEN])
105 {
106 u64 v0 = 0x736f6d6570736575ULL;
107 u64 v1 = 0x646f72616e646f6dULL;
108 u64 v2 = 0x6c7967656e657261ULL;
109 u64 v3 = 0x7465646279746573ULL;
110 u64 b = ((u64)len) << 56;
111 u64 k0 = le64_to_cpuvp(key);
112 u64 k1 = le64_to_cpuvp(key + sizeof(u64));
113 u64 m;
114 const u8 *end = data + len - (len % sizeof(u64));
115 const u8 left = len & (sizeof(u64) - 1);
116 v3 ^= k1;
117 v2 ^= k0;
118 v1 ^= k1;
119 v0 ^= k0;
120 for (; data != end; data += sizeof(u64)) {
121 m = get_unaligned_le64(data);
122 v3 ^= m;
123 SIPROUND;
124 SIPROUND;
125 v0 ^= m;
126 }
127 #if defined(CONFIG_DCACHE_WORD_ACCESS) && BITS_PER_LONG == 64
128 if (left)
129 b |= le64_to_cpu((__force __le64)(load_unaligned_zeropad(data) & bytemask_from_count(left)));
130 #else
131 switch (left) {
132 case 7: b |= ((u64)data[6]) << 48;
133 case 6: b |= ((u64)data[5]) << 40;
134 case 5: b |= ((u64)data[4]) << 32;
135 case 4: b |= get_unaligned_le32(data); break;
136 case 3: b |= ((u64)data[2]) << 16;
137 case 2: b |= get_unaligned_le16(data); break;
138 case 1: b |= data[0];
139 }
140 #endif
141 v3 ^= b;
142 SIPROUND;
143 SIPROUND;
144 v0 ^= b;
145 v2 ^= 0xff;
146 SIPROUND;
147 SIPROUND;
148 SIPROUND;
149 SIPROUND;
150 return (v0 ^ v1) ^ (v2 ^ v3);
151 }
> 152 EXPORT_SYMBOL(siphash24_unaligned);
153 #endif
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Jason A. Donenfeld <[email protected]> wrote:
>
> Siphash needs a random secret key, yes. The point is that the hash
> function remains secure so long as the secret key is kept secret.
> Other functions can't make the same guarantee, and so nervous periodic
> key rotation is necessary, but in most cases nothing is done, and so
> things just leak over time.
Actually those users that use rhashtable now have a much more
sophisticated defence against these attacks, dyanmic rehashing
when bucket length exceeds a preset limit.
Cheers,
--
Email: Herbert Xu <[email protected]>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
On Thu, 2016-12-15 at 15:57 +0800, Herbert Xu wrote:
> Jason A. Donenfeld <[email protected]> wrote:
> >
> > Siphash needs a random secret key, yes. The point is that the hash
> > function remains secure so long as the secret key is kept secret.
> > Other functions can't make the same guarantee, and so nervous
> > periodic
> > key rotation is necessary, but in most cases nothing is done, and so
> > things just leak over time.
>
> Actually those users that use rhashtable now have a much more
> sophisticated defence against these attacks, dyanmic rehashing
> when bucket length exceeds a preset limit.
>
> Cheers,
Key independent collisions won't be mitigated by picking a new secret.
A simple solution with clear security properties is ideal.
On 15.12.2016 00:29, Jason A. Donenfeld wrote:
> Hi Hannes,
>
> On Wed, Dec 14, 2016 at 11:03 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
>> I fear that the alignment requirement will be a source of bugs on 32 bit
>> machines, where you cannot even simply take a well aligned struct on a
>> stack and put it into the normal siphash(aligned) function without
>> adding alignment annotations everywhere. Even blocks returned from
>> kmalloc on 32 bit are not aligned to 64 bit.
>
> That's what the "__aligned(SIPHASH24_ALIGNMENT)" attribute is for. The
> aligned siphash function will be for structs explicitly made for
> siphash consumption. For everything else there's siphash_unaligned.
So in case you have a pointer from somewhere on 32 bit you can
essentially only guarantee it has natural alignment or max. native
alignment (based on the arch). gcc only fulfills your request for
alignment when you allocate on the stack (minus gcc bugs).
Let's say you get a pointer from somewhere, maybe embedded in a struct,
which came from kmalloc. kmalloc doesn't care about aligned attribute,
it will align according to architecture description. That said, if you
want to hash that, you would need manually align the memory returned
from kmalloc or make sure the the data is more than naturally aligned on
that architecture.
>> Can we do this a runtime check and just have one function (siphash)
>> dealing with that?
>
> Seems like the runtime branching on the aligned function would be bad
> for performance, when we likely know at compile time if it's going to
> be aligned or not. I suppose we could add that check just to the
> unaligned version, and rename it to "maybe_unaligned"? Is this what
> you have in mind?
I argue that you mostly don't know at compile time if it is correctly
aligned if the alignment requirements are larger than the natural ones.
Also, we don't even have that for memcpy, even we use it probably much
more than hashing, so I think this is overkill.
Bye,
Hannes
From: Behalf Of Jason A. Donenfeld
> Sent: 14 December 2016 18:46
...
> + ret = *chaining = siphash24((u8 *)&combined, offsetof(typeof(combined), end),
If you make the first argument 'const void *' you won't need the cast
on every call.
I'd also suggest making the key u64[2].
David
From: Linus Torvalds
> Sent: 15 December 2016 00:11
> On Wed, Dec 14, 2016 at 3:34 PM, Jason A. Donenfeld <[email protected]> wrote:
> >
> > Or does your reasonable dislike of "word" still allow for the use of
> > dword and qword, so that the current function names of:
>
> dword really is confusing to people.
>
> If you have a MIPS background, it means 64 bits. While to people with
> Windows programming backgrounds it means 32 bits.
Guess what a DWORD_PTR is on 64bit windows ...
(it is an integer type).
David
From: Hannes Frederic Sowa
> Sent: 14 December 2016 22:03
> On 14.12.2016 13:46, Jason A. Donenfeld wrote:
> > Hi David,
> >
> > On Wed, Dec 14, 2016 at 10:56 AM, David Laight <[email protected]> wrote:
> >> ...
> >>> +u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
> >> ...
> >>> + u64 k0 = get_unaligned_le64(key);
> >>> + u64 k1 = get_unaligned_le64(key + sizeof(u64));
> >> ...
> >>> + m = get_unaligned_le64(data);
> >>
> >> All these unaligned accesses are going to get expensive on architectures
> >> like sparc64.
> >
> > Yes, the unaligned accesses aren't pretty. Since in pretty much all
> > use cases thus far, the data can easily be made aligned, perhaps it
> > makes sense to create siphash24() and siphash24_unaligned(). Any
> > thoughts on doing something like that?
>
> I fear that the alignment requirement will be a source of bugs on 32 bit
> machines, where you cannot even simply take a well aligned struct on a
> stack and put it into the normal siphash(aligned) function without
> adding alignment annotations everywhere. Even blocks returned from
> kmalloc on 32 bit are not aligned to 64 bit.
Are you doing anything that will require 64bit alignment on 32bit systems?
It is unlikely that the kernel can use any simd registers that have wider
alignment requirements.
You also really don't want to request on-stack items have large alignments.
While gcc can generate code to do it, it isn't pretty.
David
On 15.12.2016 12:04, David Laight wrote:
> From: Hannes Frederic Sowa
>> Sent: 14 December 2016 22:03
>> On 14.12.2016 13:46, Jason A. Donenfeld wrote:
>>> Hi David,
>>>
>>> On Wed, Dec 14, 2016 at 10:56 AM, David Laight <[email protected]> wrote:
>>>> ...
>>>>> +u64 siphash24(const u8 *data, size_t len, const u8 key[SIPHASH24_KEY_LEN])
>>>> ...
>>>>> + u64 k0 = get_unaligned_le64(key);
>>>>> + u64 k1 = get_unaligned_le64(key + sizeof(u64));
>>>> ...
>>>>> + m = get_unaligned_le64(data);
>>>>
>>>> All these unaligned accesses are going to get expensive on architectures
>>>> like sparc64.
>>>
>>> Yes, the unaligned accesses aren't pretty. Since in pretty much all
>>> use cases thus far, the data can easily be made aligned, perhaps it
>>> makes sense to create siphash24() and siphash24_unaligned(). Any
>>> thoughts on doing something like that?
>>
>> I fear that the alignment requirement will be a source of bugs on 32 bit
>> machines, where you cannot even simply take a well aligned struct on a
>> stack and put it into the normal siphash(aligned) function without
>> adding alignment annotations everywhere. Even blocks returned from
>> kmalloc on 32 bit are not aligned to 64 bit.
>
> Are you doing anything that will require 64bit alignment on 32bit systems?
> It is unlikely that the kernel can use any simd registers that have wider
> alignment requirements.
>
> You also really don't want to request on-stack items have large alignments.
> While gcc can generate code to do it, it isn't pretty.
Hmm? Even the Intel ABI expects alignment of unsigned long long to be 8
bytes on 32 bit. Do you question that?
From: Hannes Frederic Sowa
> Sent: 15 December 2016 12:23
...
> Hmm? Even the Intel ABI expects alignment of unsigned long long to be 8
> bytes on 32 bit. Do you question that?
Yes.
The linux ABI for x86 (32 bit) only requires 32bit alignment for u64 (etc).
David
On 15.12.2016 13:28, David Laight wrote:
> From: Hannes Frederic Sowa
>> Sent: 15 December 2016 12:23
> ...
>> Hmm? Even the Intel ABI expects alignment of unsigned long long to be 8
>> bytes on 32 bit. Do you question that?
>
> Yes.
>
> The linux ABI for x86 (32 bit) only requires 32bit alignment for u64 (etc).
Hmm, u64 on 32 bit is unsigned long long and not unsigned long. Thus I
am actually not sure if the ABI would say anything about that (sorry
also for my wrong statement above).
Alignment requirement of unsigned long long on gcc with -m32 actually
seem to be 8.
From: Hannes Frederic Sowa
> Sent: 15 December 2016 12:50
> On 15.12.2016 13:28, David Laight wrote:
> > From: Hannes Frederic Sowa
> >> Sent: 15 December 2016 12:23
> > ...
> >> Hmm? Even the Intel ABI expects alignment of unsigned long long to be 8
> >> bytes on 32 bit. Do you question that?
> >
> > Yes.
> >
> > The linux ABI for x86 (32 bit) only requires 32bit alignment for u64 (etc).
>
> Hmm, u64 on 32 bit is unsigned long long and not unsigned long. Thus I
> am actually not sure if the ABI would say anything about that (sorry
> also for my wrong statement above).
>
> Alignment requirement of unsigned long long on gcc with -m32 actually
> seem to be 8.
It depends on the architecture.
For x86 it is definitely 4.
It might be 8 for sparc, ppc and/or alpha.
David
On 15.12.2016 14:56, David Laight wrote:
> From: Hannes Frederic Sowa
>> Sent: 15 December 2016 12:50
>> On 15.12.2016 13:28, David Laight wrote:
>>> From: Hannes Frederic Sowa
>>>> Sent: 15 December 2016 12:23
>>> ...
>>>> Hmm? Even the Intel ABI expects alignment of unsigned long long to be 8
>>>> bytes on 32 bit. Do you question that?
>>>
>>> Yes.
>>>
>>> The linux ABI for x86 (32 bit) only requires 32bit alignment for u64 (etc).
>>
>> Hmm, u64 on 32 bit is unsigned long long and not unsigned long. Thus I
>> am actually not sure if the ABI would say anything about that (sorry
>> also for my wrong statement above).
>>
>> Alignment requirement of unsigned long long on gcc with -m32 actually
>> seem to be 8.
>
> It depends on the architecture.
> For x86 it is definitely 4.
May I ask for a reference? I couldn't see unsigned long long being
mentioned in the ia32 abi spec that I found. I agree that those accesses
might be synthetically assembled by gcc and for me the alignment of 4
would have seemed natural. But my gcc at least in 32 bit mode disagrees
with that.
> It might be 8 for sparc, ppc and/or alpha.
This is something to find out...
Right now ipv6 addresses have an alignment of 4. So we couldn't even
naturally pass them to siphash but would need to copy them around, which
I feel like a source of bugs.
Bye,
Hannes
From: Hannes Frederic Sowa
> Sent: 15 December 2016 14:57
> On 15.12.2016 14:56, David Laight wrote:
> > From: Hannes Frederic Sowa
> >> Sent: 15 December 2016 12:50
> >> On 15.12.2016 13:28, David Laight wrote:
> >>> From: Hannes Frederic Sowa
> >>>> Sent: 15 December 2016 12:23
> >>> ...
> >>>> Hmm? Even the Intel ABI expects alignment of unsigned long long to be 8
> >>>> bytes on 32 bit. Do you question that?
> >>>
> >>> Yes.
> >>>
> >>> The linux ABI for x86 (32 bit) only requires 32bit alignment for u64 (etc).
> >>
> >> Hmm, u64 on 32 bit is unsigned long long and not unsigned long. Thus I
> >> am actually not sure if the ABI would say anything about that (sorry
> >> also for my wrong statement above).
> >>
> >> Alignment requirement of unsigned long long on gcc with -m32 actually
> >> seem to be 8.
> >
> > It depends on the architecture.
> > For x86 it is definitely 4.
>
> May I ask for a reference?
Ask anyone who has had to do compatibility layers to support 32bit
binaries on 64bit systems.
> I couldn't see unsigned long long being
> mentioned in the ia32 abi spec that I found. I agree that those accesses
> might be synthetically assembled by gcc and for me the alignment of 4
> would have seemed natural. But my gcc at least in 32 bit mode disagrees
> with that.
Try (retyped):
echo 'struct { long a; long long b; } s; int bar { return sizeof s; }' >foo.c
gcc [-m32] -O2 -S foo.c; cat foo.s
And look at what is generated.
> Right now ipv6 addresses have an alignment of 4. So we couldn't even
> naturally pass them to siphash but would need to copy them around, which
> I feel like a source of bugs.
That is more of a problem on systems that don't support misaligned accesses.
Reading the 64bit values with two explicit 32bit reads would work.
I think you can get gcc to do that by adding an aligned(4) attribute to the
structure member.
David
On 15.12.2016 16:41, David Laight wrote:
> Try (retyped):
>
> echo 'struct { long a; long long b; } s; int bar { return sizeof s; }' >foo.c
> gcc [-m32] -O2 -S foo.c; cat foo.s
>
> And look at what is generated.
I used __alignof__(unsigned long long) with -m32.
>> Right now ipv6 addresses have an alignment of 4. So we couldn't even
>> naturally pass them to siphash but would need to copy them around, which
>> I feel like a source of bugs.
>
> That is more of a problem on systems that don't support misaligned accesses.
> Reading the 64bit values with two explicit 32bit reads would work.
> I think you can get gcc to do that by adding an aligned(4) attribute to the
> structure member.
Yes, and that is actually my fear, because we support those
architectures. I can't comment on that as I don't understand enough of this.
If someone finds a way to cause misaligned reads on a small box this
seems (maybe depending on sysctls they get fixed up or panic) to be a
much bigger issue than having a hash DoS.
Thanks,
Hannes
Hi David & Hannes,
This conversation is veering off course. I think this doesn't really
matter at all. Gcc converts u64 into essentially a pair of u32 on
32-bit platforms, so the alignment requirements for 32-bit is at a
maximum 32 bits. On 64-bit platforms the alignment requirements are
related at a maximum to the biggest register size, so 64-bit
alignment. For this reason, no matter the behavior of __aligned(8),
we're okay. Likewise, even without __aligned(8), if gcc aligns structs
by their biggest member, then we get 4 byte alignment on 32-bit and 8
byte alignment on 64-bit, which is fine. There's no 32-bit platform
that will trap on a 64-bit unaligned access because there's no such
thing as a 64-bit access there. In short, we're fine.
(The reason in6_addr aligns itself to 4 bytes on 64-bit platforms is
that it's defined as being u32 blah[4]. If we added a u64 blah[2],
we'd get 8 byte alignment, but that's not in the header. Feel free to
start a new thread about this issue if you feel this ought to be added
for whatever reason.)
One optimization that's been suggested on this list is that instead of
u8 key[16] and requiring the alignment attribute, I should just use
u64 key[2]. This seems reasonable to me, and it will also save the
endian conversion call. These keys generally aren't transmitted over a
network, so I don't think a byte-wise encoding is particularly
important.
The other suggestion I've seen is that I make the functions take a
const void * instead of a const u8 * for the data, in order to save
ugly casts. I'll do this too.
Meanwhile Linus has condemned our 4dwords/2qwords naming, and I'll
need to think of something different. The best I can think of right
now is siphash_4_u32/siphash_2_u64, but I don't find it especially
pretty. Open to suggestions.
Regards,
Jason
Hi David,
On Thu, Dec 15, 2016 at 11:14 AM, David Laight <[email protected]> wrote:
> From: Behalf Of Jason A. Donenfeld
>> Sent: 14 December 2016 18:46
> ...
>> + ret = *chaining = siphash24((u8 *)&combined, offsetof(typeof(combined), end),
>
> If you make the first argument 'const void *' you won't need the cast
> on every call.
>
> I'd also suggest making the key u64[2].
I'll do both. Thanks for the suggestion.
Jason
Hello,
On 15.12.2016 19:50, Jason A. Donenfeld wrote:
> Hi David & Hannes,
>
> This conversation is veering off course.
Why?
> I think this doesn't really
> matter at all. Gcc converts u64 into essentially a pair of u32 on
> 32-bit platforms, so the alignment requirements for 32-bit is at a
> maximum 32 bits. On 64-bit platforms the alignment requirements are
> related at a maximum to the biggest register size, so 64-bit
> alignment. For this reason, no matter the behavior of __aligned(8),
> we're okay. Likewise, even without __aligned(8), if gcc aligns structs
> by their biggest member, then we get 4 byte alignment on 32-bit and 8
> byte alignment on 64-bit, which is fine. There's no 32-bit platform
> that will trap on a 64-bit unaligned access because there's no such
> thing as a 64-bit access there. In short, we're fine.
ARM64 and x86-64 have memory operations that are not vector operations
that operate on 128 bit memory.
How do you know that the compiler for some architecture will not chose a
more optimized instruction to load a 64 bit memory value into two 32 bit
registers if you tell the compiler it is 8 byte aligned but it actually
isn't? I don't know the answer but telling the compiler some data is 8
byte aligned while it isn't really pretty much seems like a call for
trouble.
Why can't a compiler not vectorize this code if it can prove that it
doesn't conflict with other register users?
Bye,
Hannes
On Thu, Dec 15, 2016 at 9:31 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> ARM64 and x86-64 have memory operations that are not vector operations
> that operate on 128 bit memory.
Fair enough. imull I guess.
> How do you know that the compiler for some architecture will not chose a
> more optimized instruction to load a 64 bit memory value into two 32 bit
> registers if you tell the compiler it is 8 byte aligned but it actually
> isn't? I don't know the answer but telling the compiler some data is 8
> byte aligned while it isn't really pretty much seems like a call for
> trouble.
If a compiler is in the business of using special 64-bit instructions
on 64-bit aligned data, then it is also the job of the compiler to
align structs to 64-bits when passed __aligned(8), which is what we've
done in this code. If the compiler were to hypothetically choose to
ignore that and internally convert it to a __aligned(4), then it would
only be able to do so with the knowledge that it will never use 64-bit
aligned data instructions. But so far as I can tell, gcc always
respects __aligned(8), which is why I use it in this patchset.
I think there might have been confusion here, because perhaps someone
was hoping that since in6_addr is 128-bits, that the __aligned
attribute would not be required and that the struct would just
automatically be aligned to at least 8 bytes. But in fact, as I
mentioned, in6_addr is actually composed of u32[4] and not u64[2], so
it will only be aligned to 4 bytes, making the __aligned(8) necessary.
I think for the purposes of this patchset, this is a solved problem.
There's the unaligned version of the function if you don't know about
the data, and there's the aligned version if you're using
__aligned(SIPHASH_ALIGNMENT) on your data. Plain and simple.
Jason
On Thu, Dec 15, 2016 at 09:43:04PM +0100, Jason A. Donenfeld wrote:
> On Thu, Dec 15, 2016 at 9:31 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
> > ARM64 and x86-64 have memory operations that are not vector operations
> > that operate on 128 bit memory.
>
> Fair enough. imull I guess.
imull is into rdx:rax, not memory. I suspect he's talking about
cmpxchg16b.
On 15.12.2016 22:04, Peter Zijlstra wrote:
> On Thu, Dec 15, 2016 at 09:43:04PM +0100, Jason A. Donenfeld wrote:
>> On Thu, Dec 15, 2016 at 9:31 PM, Hannes Frederic Sowa
>> <[email protected]> wrote:
>>> ARM64 and x86-64 have memory operations that are not vector operations
>>> that operate on 128 bit memory.
>>
>> Fair enough. imull I guess.
>
> imull is into rdx:rax, not memory. I suspect he's talking about
> cmpxchg16b.
Exactly and I think I saw a ll/sc 128 bit on armv8 to atomically
manipulate linked lists.
Bye,
Hannes
On Thu, Dec 15, 2016 at 07:50:36PM +0100, Jason A. Donenfeld wrote:
> There's no 32-bit platform
> that will trap on a 64-bit unaligned access because there's no such
> thing as a 64-bit access there. In short, we're fine.
ARMv7 LPAE is a 32bit architecture that has 64bit load/stores IIRC.
x86 has cmpxchg8b that can do 64bit things and very much wants the u64
aligned.
Also, IIRC we have a few platforms where u64 doesn't carry 8 byte
alignment, m68k or something like that, but yes, you likely don't care.
Just to make life interesting...
On Thu, Dec 15, 2016 at 10:09 PM, Peter Zijlstra <[email protected]> wrote:
> On Thu, Dec 15, 2016 at 07:50:36PM +0100, Jason A. Donenfeld wrote:
>> There's no 32-bit platform
>> that will trap on a 64-bit unaligned access because there's no such
>> thing as a 64-bit access there. In short, we're fine.
>
> ARMv7 LPAE is a 32bit architecture that has 64bit load/stores IIRC.
>
> x86 has cmpxchg8b that can do 64bit things and very much wants the u64
> aligned.
>
> Also, IIRC we have a few platforms where u64 doesn't carry 8 byte
> alignment, m68k or something like that, but yes, you likely don't care.
Indeed, I stand corrected. But in any case, the use of __aligned(8) in
the patchset ensures that things are fixed and that we don't have this
issue.
On Thu, Dec 15, 2016 at 1:11 PM, Jason A. Donenfeld <[email protected]> wrote:
>
> Indeed, I stand corrected. But in any case, the use of __aligned(8) in
> the patchset ensures that things are fixed and that we don't have this
> issue.
I think you can/should just use the natural alignment for "u64".
For architectures that need 8-byte alignment, u64 will already be
properly aligned. For architectures (like x86-32) that only need
4-byte alignment, you get it.
Linus
On Thu, Dec 15, 2016 at 10:14 PM, Linus Torvalds
<[email protected]> wrote:
> I think you can/should just use the natural alignment for "u64".
>
> For architectures that need 8-byte alignment, u64 will already be
> properly aligned. For architectures (like x86-32) that only need
> 4-byte alignment, you get it.
I should have added mention of that with my previous email. For the
parameters that are always a multiple of u64 -- namely, the key -- I
now do that in v5 of the patchset. So this is already done.
On 15.12.2016 21:43, Jason A. Donenfeld wrote:
> On Thu, Dec 15, 2016 at 9:31 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
>> ARM64 and x86-64 have memory operations that are not vector operations
>> that operate on 128 bit memory.
>
> Fair enough. imull I guess.
>
>> How do you know that the compiler for some architecture will not chose a
>> more optimized instruction to load a 64 bit memory value into two 32 bit
>> registers if you tell the compiler it is 8 byte aligned but it actually
>> isn't? I don't know the answer but telling the compiler some data is 8
>> byte aligned while it isn't really pretty much seems like a call for
>> trouble.
>
> If a compiler is in the business of using special 64-bit instructions
> on 64-bit aligned data, then it is also the job of the compiler to
> align structs to 64-bits when passed __aligned(8), which is what we've
> done in this code. If the compiler were to hypothetically choose to
> ignore that and internally convert it to a __aligned(4), then it would
> only be able to do so with the knowledge that it will never use 64-bit
> aligned data instructions. But so far as I can tell, gcc always
> respects __aligned(8), which is why I use it in this patchset.
>
> I think there might have been confusion here, because perhaps someone
> was hoping that since in6_addr is 128-bits, that the __aligned
> attribute would not be required and that the struct would just
> automatically be aligned to at least 8 bytes. But in fact, as I
> mentioned, in6_addr is actually composed of u32[4] and not u64[2], so
> it will only be aligned to 4 bytes, making the __aligned(8) necessary.
>
> I think for the purposes of this patchset, this is a solved problem.
> There's the unaligned version of the function if you don't know about
> the data, and there's the aligned version if you're using
> __aligned(SIPHASH_ALIGNMENT) on your data. Plain and simple.
And I was exactly questioning this.
static unsigned int inet6_hash_frag(__be32 id, const struct in6_addr *saddr,
const struct in6_addr *daddr)
{
net_get_random_once(&ip6_frags.rnd, sizeof(ip6_frags.rnd));
return jhash_3words(ipv6_addr_hash(saddr), ipv6_addr_hash(daddr),
(__force u32)id, ip6_frags.rnd);
}
This function had a hash DoS (and kind of still has), but it has been
mitigated by explicit checks, I hope.
So you start looking for all the pointers where ipv6 addresses could
come from and find some globally defined struct where I would need to
put the aligned(SIPHASH_ALIGNMENT) into to make this work on 32 bit
code? Otherwise just the unaligned version is safe on 32 bit code.
Who knows this? It isn't even obvious by looking at the header!
I would be interested if the compiler can actually constant-fold the
address of the stack allocation with an simple if () or some
__builtin_constant_p fiddeling, so we don't have this constant review
overhead to which function we pass which data. This would also make
this whole discussion mood.
Bye,
Hannes
On Thu, Dec 15, 2016 at 10:17 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> And I was exactly questioning this.
>
> static unsigned int inet6_hash_frag(__be32 id, const struct in6_addr *saddr,
> const struct in6_addr *daddr)
> {
> net_get_random_once(&ip6_frags.rnd, sizeof(ip6_frags.rnd));
> return jhash_3words(ipv6_addr_hash(saddr), ipv6_addr_hash(daddr),
> (__force u32)id, ip6_frags.rnd);
> }
For this example, the replacement is the function entitled siphash_4u32:
static unsigned int inet6_hash_frag(__be32 id, const struct in6_addr *saddr,
const struct in6_addr *daddr)
{
net_get_random_once(&ip6_frags.rnd, sizeof(ip6_frags.rnd));
return siphash_4u32(ipv6_addr_hash(saddr), ipv6_addr_hash(daddr),
(__force u32)id, 0, ip6_frags.rnd);
}
And then you make ip6_frags.rnd be of type siphash_key_t. Then
everything is taken care of and works beautifully. Please see v5 of
this patchset.
> I would be interested if the compiler can actually constant-fold the
> address of the stack allocation with an simple if () or some
> __builtin_constant_p fiddeling, so we don't have this constant review
> overhead to which function we pass which data. This would also make
> this whole discussion moot.
I'll play with it to see if the compiler is capable of doing that.
Does anybody know off hand if it is or if there are other examples of
the compiler doing that?
In any case, for all current replacement of jhash_1word, jhash_2words,
jhash_3words, there's the siphash_2u32 or siphash_4u32 functions. This
covers the majority of cases.
For replacements of md5_transform, either the data is small and can
fit in siphash_Nu{32,64}, or it can be put into a struct explicitly
aligned on the stack.
For the remaining use of jhash_nwords, either siphash() can be used or
siphash_unaligned() can be used if the source is of unknown alignment.
Both functions have their alignment requirements (or lack thereof)
documented in a docbook comment.
I'll look into the constant folding to see if it actually works. If it
does, I'll use it. If not, I believe the current solution works.
How's that sound?
Jason
On 15.12.2016 22:25, Jason A. Donenfeld wrote:
> On Thu, Dec 15, 2016 at 10:17 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
>> And I was exactly questioning this.
>>
>> static unsigned int inet6_hash_frag(__be32 id, const struct in6_addr *saddr,
>> const struct in6_addr *daddr)
>> {
>> net_get_random_once(&ip6_frags.rnd, sizeof(ip6_frags.rnd));
>> return jhash_3words(ipv6_addr_hash(saddr), ipv6_addr_hash(daddr),
>> (__force u32)id, ip6_frags.rnd);
>> }
>
> For this example, the replacement is the function entitled siphash_4u32:
>
> static unsigned int inet6_hash_frag(__be32 id, const struct in6_addr *saddr,
> const struct in6_addr *daddr)
> {
> net_get_random_once(&ip6_frags.rnd, sizeof(ip6_frags.rnd));
> return siphash_4u32(ipv6_addr_hash(saddr), ipv6_addr_hash(daddr),
> (__force u32)id, 0, ip6_frags.rnd);
> }
>
> And then you make ip6_frags.rnd be of type siphash_key_t. Then
> everything is taken care of and works beautifully. Please see v5 of
> this patchset.
Sorry to not be specific enough, the Hash-DoS is in ipv6_addr_hash.
Maybe it was a silly example to start with, sorry. But anyway, your
proposal wouldn't have prevented the hash DoS. I wanted to show how it
can be difficult to make sure that all pointers come from an appropriate
aligned memory region.
The idea would be to actually factor out the key in the data structure
and align it with __aligned(SIPHASH_ALIGNMENT), make sure the padding
bits are all equal zero to not cause any bugs and irregularities with
the corresponding equality function. This might need some serious review
when switching to siphash to actually make use of it and prevent
HashDoS. Or simply use the unaligned version always...
>> I would be interested if the compiler can actually constant-fold the
>> address of the stack allocation with an simple if () or some
>> __builtin_constant_p fiddeling, so we don't have this constant review
>> overhead to which function we pass which data. This would also make
>> this whole discussion moot.
>
> I'll play with it to see if the compiler is capable of doing that.
> Does anybody know off hand if it is or if there are other examples of
> the compiler doing that?
Not of the top of my head, but it should be easy to test.
> In any case, for all current replacement of jhash_1word, jhash_2words,
> jhash_3words, there's the siphash_2u32 or siphash_4u32 functions. This
> covers the majority of cases.
Agreed and this is also totally fine by me.
> For replacements of md5_transform, either the data is small and can
> fit in siphash_Nu{32,64}, or it can be put into a struct explicitly
> aligned on the stack.
> For the remaining use of jhash_nwords, either siphash() can be used or
> siphash_unaligned() can be used if the source is of unknown alignment.
> Both functions have their alignment requirements (or lack thereof)
> documented in a docbook comment.
I think the warning needs to be bigger, seriously. Most of the people
develop on 64 bit arch, where it will just work during testing and break
later on 32 bit. ;)
> I'll look into the constant folding to see if it actually works. If it
> does, I'll use it. If not, I believe the current solution works.
>
> How's that sound?
I am still very much concerned about the API.
By the way, if you target net-next, it is currently closed. So no need
to hurry.
Bye,
Hannes
Hi Hannes,
Good news.
On Thu, Dec 15, 2016 at 10:45 PM, Hannes Frederic Sowa
<[email protected]> wrote:
>> How's that sound?
>
> I am still very much concerned about the API.
Thanks for pushing me and putting up with my daftness... the constant
folding works absolutely perfectly. I've run several tests. When gcc
knows that a struct is aligned (say, via __aligned(8)), then it erases
the branch and makes a direct jump to the aligned code. When it's
uncertain, it evaluates at runtime. So, now there is a single
siphash() function that chooses the best one automatically. Behind the
scene there's siphash_aligned and siphash_unaligned, but nobody needs
to call these directly. (Should I rename these to have a double
underscore prefix?) On platforms that have
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, of course all of this
disappears and everything goes directly to the aligned version.
So, I think this assuages your concerns entirely. A single API entry
point that does the right thing.
Whew! Good thinking, and thanks again for the suggestion.
Jason
On Thu, Dec 15, 2016 at 10:45 PM, Hannes Frederic Sowa
<[email protected]> wrote:
> By the way, if you target net-next, it is currently closed. So no need
> to hurry.
Honestly I have no idea what I'm targeting. The hash function touches
lib/. The secure_seq stuff touches net/. The rng stuff touches
random.c. Shall this be for net-next? For lib-next (doesn't exist)?
For tytso-next? Since a lot of feedback has come from netdev people, I
suspect net-next is the correct answer. In that case, I'll ask Ted for
his sign-off to touch random.c, and then we'll get this queued up in
net-next. Please correct me if this doesn't actually resemble how
things work around here...
Jason
On 16.12.2016 00:43, Jason A. Donenfeld wrote:
> Hi Hannes,
>
> Good news.
>
> On Thu, Dec 15, 2016 at 10:45 PM, Hannes Frederic Sowa
> <[email protected]> wrote:
>>> How's that sound?
>>
>> I am still very much concerned about the API.
>
> Thanks for pushing me and putting up with my daftness... the constant
> folding works absolutely perfectly. I've run several tests. When gcc
> knows that a struct is aligned (say, via __aligned(8)), then it erases
> the branch and makes a direct jump to the aligned code. When it's
> uncertain, it evaluates at runtime. So, now there is a single
> siphash() function that chooses the best one automatically. Behind the
> scene there's siphash_aligned and siphash_unaligned, but nobody needs
> to call these directly. (Should I rename these to have a double
> underscore prefix?) On platforms that have
> CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, of course all of this
> disappears and everything goes directly to the aligned version.
>
> So, I think this assuages your concerns entirely. A single API entry
> point that does the right thing.
>
> Whew! Good thinking, and thanks again for the suggestion.
Awesome, thanks for trying this out. This basically resolves my concern
API-wise so far.
Hannes out. ;)
On Thu, 15 Dec 2016, Jason A. Donenfeld wrote:
> > I'd still drop the "24" unless you really think we're going to have
> > multiple variants coming into the kernel.
>
> Okay. I don't have a problem with this, unless anybody has some reason
> to the contrary.
What if the 2/4-round version falls and we need more rounds to withstand
future cryptoanalysis? We'd then have siphash_ and siphash48_ functions,
no? My amateurish bike-shedding argument would be "let's keep the 24 then" :-)
C.
--
BOFH excuse #354:
Chewing gum on /dev/sd3c