LinuxLists.cc - AT_ENTROPY1 and AT_ENTROPY2 values for include/linux/auxvec.h

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Subject: Re: AT_ENTROPY1 and AT_ENTROPY2 values for include/linux/auxvec.h

On Mon, 2007-06-18 at 01:40 +0200, Alexander Gabert wrote:
> Hello glibc and kernel maintainers,
>
> could you please add two AT_ entries to include/linux/auxvec.h in the
> upstream kernel and the respective elf/elf.h definitions in glibc.

while I'm not per se against adding such aux vectors, I think it's a bad
mistake to make them a config option (and 2 options at that!!)

Stack protector is very widely deployed today
(Fedora,RHEL,SLES,OpenSUSE,Gentoo etc), so I can sure see the point of
helping it a bit... but I'd like to see a little more data on how the
current approach isn't sufficient.

2007-06-18 01:28:21

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Subject: Re: AT_ENTROPY1 and AT_ENTROPY2 values for include/linux/auxvec.h

Arjan van de Ven schrieb:
> On Mon, 2007-06-18 at 01:40 +0200, Alexander Gabert wrote:
>
>> Hello glibc and kernel maintainers,
>>
>> could you please add two AT_ entries to include/linux/auxvec.h in the
>> upstream kernel and the respective elf/elf.h definitions in glibc.
>>
>
>
> while I'm not per se against adding such aux vectors, I think it's a bad
> mistake to make them a config option (and 2 options at that!!)
>
Well our glibc patch (still under development, here comes a snippet)
will conditionally check for the auxv and if not "fall back" to normal
SSP entropy:

- /* Set up the stack checker's canary. */
- uintptr_t stack_chk_guard = _dl_setup_stack_chk_guard ();
+ /* Set up the stack checker's canary, optional kernel entropy */
+ uintptr_t stack_chk_guard;
+
+ if (GLRO(dl_entropy) != 0) {
+ stack_chk_guard = GLRO(dl_entropy);
+ }
+ else {
+ stack_chk_guard = _dl_setup_stack_chk_guard ();
+ }

Hence the config option for the kernel- it's philosophy at Gentoo to
make choices available to users how they want their systems to behave,
even on the expense of added complexity and need to "understand" how
things work in the first place.

If you add the aux vector behaviour as a default, there would surely be
a backport of the default behaviour to the more "Gentoo flavoured"
choice-based system of activating/deactivating it to your own needs.

For your second question, why two config options: entropy is a precious
resource and many critical apps rely on it.
Until SSPx (http://dev.gentoo.org/~pappy/sspx/ssxp.pdf) is not
available, we don't want to force users to have two vector entries with
one containing unneeded (wasted?) entropy. SSP already works good, so
if this stuff makes it's way into the kernel or kernel and glibc folks
tell me which numbers i can use, i can make my patches and add the logic
to Gentoo kernel sources and glibc.

Sincere thanks,

Alex

2007-06-18 01:40:57

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Subject: Re: AT_ENTROPY1 and AT_ENTROPY2 values for include/linux/auxvec.h

> Hence the config option for the kernel- it's philosophy at Gentoo to
> make choices available to users how they want their systems to behave,
> even on the expense of added complexity and need to "understand" how
> things work in the first place.

While I am not opposed to choice, I am opposed to having too finegrained
kernel config options. In your view, every single kernel patch would be
a config option... I much rather have config options for "important" big
changes, not for something this small. Another argument is that this
kind of userspace interface is better off being always there or never;
making this variable serves no-one.

--
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

2007-06-18 10:36:22

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Subject: Re: AT_ENTROPY1 and AT_ENTROPY2 values for include/linux/auxvec.h

Arjan van de Ven schrieb:
>> Hence the config option for the kernel- it's philosophy at Gentoo to
>> make choices available to users how they want their systems to behave,
>> even on the expense of added complexity and need to "understand" how
>> things work in the first place.
>>
>
> While I am not opposed to choice, I am opposed to having too finegrained
> kernel config options. In your view, every single kernel patch would be
> a config option... I much rather have config options for "important" big
> changes, not for something this small. Another argument is that this
> kind of userspace interface is better off being always there or never;
> making this variable serves no-one.
>
>
>
>
Hi again,

as said, i'm not voting for getting the specific example patch into
kernel source.
All i came for and would like to see is the two numbers into the
upstream header file to avoid future namespace clashes (as said in the
original mail).

I honestly don't know how to follow the discussion to implement this
kind of entropy given via auxv to userland- if you (the kernel devs)
think it makes sense the way you want it you as upstream devs can do it
all the way you like it- i can always change it with a patch for my own
needs in my own sources. I can't say anything at all about all of this
because i don't know what is important from your point of view as kernel
maintainers and what is not. I understand your concerns and know that
we are talking from different perspectives, thus it is probably normal
that our interests and technical solutions vary.

However, as said, the only thing important for me is to not use
"arbitrary" chosen numbers for the AT_ENTROPY1 and 2 values and later
have problems when my "private" numbers suddenly are assigned to a
different thing by "official" kernel devs. That would be bad for me and
this is what i want to avoid in the first place.

So please tell me what i can do about the requirements and the time and
what the usual process is for asking how to get the numbers into the
kernel so i can start using them for my own work.

Thanks in advance,

Alex

2007-06-20 15:34:29

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Subject: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

Hi,

http://dev.gentoo.org/~pappy/kernel/linux-2.6.21.5-get_urandom_long-AT_ENTROPY.patch

this patch adds the function drivers/char/random.c:get_random_long()
and adds an AT_ENTROPY field in the auxv without config option
(the config option was removed as suggested by Arjan on LKML).

README: get_random_long() and AT_ENTROPY support for auxv
NAME: Alexander Gabert
EMAIL: [email protected]

diff -Nru linux-2.6.21.5.ORIG/drivers/char/random.c
linux-2.6.21.5/drivers/char/random.c
--- linux-2.6.21.5.ORIG/drivers/char/random.c 2007-06-11
20:37:06.000000000 +0200
+++ linux-2.6.21.5/drivers/char/random.c 2007-06-20
17:00:35.000000000 +0200
@@ -1654,6 +1654,53 @@
}

/*
+ * get_random_long() returns a randomized unsigned long word.
+ * It recycles it's entropy cache for a given time period and
+ * uses half_md4_transform to generate a unique return value.
+ * Every REKEY_INTERVAL the cache is reloaded with fresh
+ * randomization data using get_random_bytes().
+ * This function is not intended for strong cryptographic routines.
+ */
+unsigned long get_random_long(void)
+{
+ /* remember the last time we refreshed the cache with random entropy */
+ static time_t rekey_time;
+
+ time_t t;
+
+ /*
+ * the following data in the buffer is unchanged during REKEY_INTERVAL:
+ * |----|----|KKKK|KKKK|KKKK|KKKK|KKKK|KKKK|----|----|----|----|
+ * ___0____1____2____3____4____5____6____7____8____9___10___11__
+ *
+ * the following data is updated during the first half_md4_transform call
+ * |----|YYYY|----|----|----|----|----|----|ZZZZ|ZZZZ|ZZZZ|ZZZZ|
+ * ___0____1____2____3____4____5____6____7____8____9___10___11__
+ *
+ * the following data is updated during the second half_md4_transform
+ * |XXXX|----|----|----|----|----|----|----|ZZZZ|ZZZZ|ZZZZ|ZZZZ|
+ * ___0____1____2____3____4____5____6____7____8____9___10___11__
+ */
+ static __u32 entropycache[12];
+
+ /* get the current time in seconds */
+ t = get_seconds();
+
+ /* check for REKEY_INTERVAL */
+ if (t && (!rekey_time || ((t - rekey_time) > REKEY_INTERVAL))) {
+ rekey_time = t;
+ /* refresh with random entropy */
+ get_random_bytes(entropycache, sizeof(entropycache));
+ }
+
+ /* transform the buffer to a new state, thus generating new return
value */
+ entropycache[1] = half_md4_transform(entropycache+8, entropycache);
+ entropycache[0] = half_md4_transform(entropycache+8, entropycache);
+
+ return *(unsigned long *)entropycache;
+}
+
+/*
* randomize_range() returns a start address such that
*
* [...... <range> .....]
diff -Nru linux-2.6.21.5.ORIG/fs/binfmt_elf.c linux-2.6.21.5/fs/binfmt_elf.c
--- linux-2.6.21.5.ORIG/fs/binfmt_elf.c 2007-06-11 20:37:06.000000000
+0200
+++ linux-2.6.21.5/fs/binfmt_elf.c 2007-06-20 17:02:59.000000000 +0200
@@ -201,6 +201,7 @@
NEW_AUX_ENT(AT_GID, tsk->gid);
NEW_AUX_ENT(AT_EGID, tsk->egid);
NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ NEW_AUX_ENT(AT_ENTROPY, get_random_long());
if (k_platform) {
NEW_AUX_ENT(AT_PLATFORM,
(elf_addr_t)(unsigned long)u_platform);
diff -Nru linux-2.6.21.5.ORIG/include/linux/auxvec.h
linux-2.6.21.5/include/linux/auxvec.h
--- linux-2.6.21.5.ORIG/include/linux/auxvec.h 2007-06-11
20:37:06.000000000 +0200
+++ linux-2.6.21.5/include/linux/auxvec.h 2007-06-20
16:47:44.000000000 +0200
@@ -26,6 +26,8 @@

#define AT_SECURE 23 /* secure mode boolean */

-#define AT_VECTOR_SIZE 44 /* Size of auxiliary table. */
+#define AT_ENTROPY 24 /* kernel entropy in auxv */
+
+#define AT_VECTOR_SIZE 45 /* Size of auxiliary table in. */

#endif /* _LINUX_AUXVEC_H */
diff -Nru linux-2.6.21.5.ORIG/include/linux/random.h
linux-2.6.21.5/include/linux/random.h
--- linux-2.6.21.5.ORIG/include/linux/random.h 2007-06-11
20:37:06.000000000 +0200
+++ linux-2.6.21.5/include/linux/random.h 2007-06-20
16:19:02.000000000 +0200
@@ -67,6 +67,9 @@
#endif

unsigned int get_random_int(void);
+
+unsigned long get_random_long(void);
+
unsigned long randomize_range(unsigned long start, unsigned long end,
unsigned long len);

u32 random32(void);

2007-06-20 15:41:42

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Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Wed, 2007-06-20 at 17:34 +0200, Alexander Gabert wrote:
> Hi,
>
> http://dev.gentoo.org/~pappy/kernel/linux-2.6.21.5-get_urandom_long-AT_ENTROPY.patch
>
> this patch adds the function drivers/char/random.c:get_random_long()
> and adds an AT_ENTROPY field in the auxv without config option
> (the config option was removed as suggested by Arjan on LKML).

your patch has some whitespace damage it seems...
other than that I can agree with the approach.

--
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

2007-06-20 16:40:18

by Linus Torvalds

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Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Wed, 20 Jun 2007, Alexander Gabert wrote:
>
> this patch adds the function drivers/char/random.c:get_random_long()

It's totally whitespace-damaged, and I wonder why the "int" vs "long" is
so important. Also, what are the performance implications for execve?

Linus

2007-06-20 17:04:36

by Eric Dumazet

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Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Wed, 20 Jun 2007 17:34:13 +0200
Alexander Gabert <[email protected]> wrote:

> Hi,

Hello Alexander

>
> http://dev.gentoo.org/~pappy/kernel/linux-2.6.21.5-get_urandom_long-AT_ENTROPY.patch
>
> this patch adds the function drivers/char/random.c:get_random_long()
> and adds an AT_ENTROPY field in the auxv without config option
> (the config option was removed as suggested by Arjan on LKML).
>
> README: get_random_long() and AT_ENTROPY support for auxv
> NAME: Alexander Gabert
> EMAIL: [email protected]
>
>
>
> diff -Nru linux-2.6.21.5.ORIG/drivers/char/random.c
> linux-2.6.21.5/drivers/char/random.c
> --- linux-2.6.21.5.ORIG/drivers/char/random.c 2007-06-11
> 20:37:06.000000000 +0200
> +++ linux-2.6.21.5/drivers/char/random.c 2007-06-20
> 17:00:35.000000000 +0200
> @@ -1654,6 +1654,53 @@
> }
>
> /*
> + * get_random_long() returns a randomized unsigned long word.
> + * It recycles it's entropy cache for a given time period and
> + * uses half_md4_transform to generate a unique return value.
> + * Every REKEY_INTERVAL the cache is reloaded with fresh
> + * randomization data using get_random_bytes().
> + * This function is not intended for strong cryptographic routines.
> + */
> +unsigned long get_random_long(void)
> +{
> + /* remember the last time we refreshed the cache with random entropy */
> + static time_t rekey_time;
> +
> + time_t t;
> +
> + /*
> + * the following data in the buffer is unchanged during REKEY_INTERVAL:
> + * |----|----|KKKK|KKKK|KKKK|KKKK|KKKK|KKKK|----|----|----|----|
> + * ___0____1____2____3____4____5____6____7____8____9___10___11__
> + *
> + * the following data is updated during the first half_md4_transform call
> + * |----|YYYY|----|----|----|----|----|----|ZZZZ|ZZZZ|ZZZZ|ZZZZ|
> + * ___0____1____2____3____4____5____6____7____8____9___10___11__
> + *
> + * the following data is updated during the second half_md4_transform
> + * |XXXX|----|----|----|----|----|----|----|ZZZZ|ZZZZ|ZZZZ|ZZZZ|
> + * ___0____1____2____3____4____5____6____7____8____9___10___11__
> + */
> + static __u32 entropycache[12];
> +
> + /* get the current time in seconds */
> + t = get_seconds();
> +
> + /* check for REKEY_INTERVAL */
> + if (t && (!rekey_time || ((t - rekey_time) > REKEY_INTERVAL))) {
> + rekey_time = t;
> + /* refresh with random entropy */
> + get_random_bytes(entropycache, sizeof(entropycache));
> + }

Maybe this rekeying can be added in rekey_seq_generator(), so that you dont have to test rekey_time each time get_random_long() is called. You probably could refresh only 8 values, not the full 12 values.

> +
> + /* transform the buffer to a new state, thus generating new return
> value */
> + entropycache[1] = half_md4_transform(entropycache+8, entropycache);
> + entropycache[0] = half_md4_transform(entropycache+8, entropycache);
> +
> + return *(unsigned long *)entropycache;

This is not valid on some arches, as entropycache[] alignment (u32 -> 4) might be smaller then alignment for a long (4 or 8).

This also adds about 400 instructions (half_md4_transform() is about 200 instructions, about 700 bytes of code on x86_64) in exec() path, but this is probably minor given the cost of exec()

I am not sure why you unconditionally call half_md4_transform() twice, since the entropycache[1] wont be used on 32bits platforms.

I suggest spliting your entropycache into two parts :

One part, with 8 u32, that is read_mostly (and shared by all cpus), updated once every 300 seconds in rekey_seq_generator()
static u32 entropycache_shared[8] __read_mostly;

One part, with (16/sizeof(long)) long, percpu to avoid false sharing between cpus.
static DEFINE_PER_CPU(unsigned long , entropycache_pcpu)[16 / sizeof(unsigned long)];

then call half_md4_transform() once :

half_md4_transform((u32 *)entropycache_pcpu, entropycache_shared);
return entropycache_pcpu[0];

2007-06-20 20:31:16

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Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Wed, Jun 20, 2007 at 05:34:13PM +0200, Alexander Gabert wrote:
> Hi,
>
> http://dev.gentoo.org/~pappy/kernel/linux-2.6.21.5-get_urandom_long-AT_ENTROPY.patch
>
> this patch adds the function drivers/char/random.c:get_random_long()
> and adds an AT_ENTROPY field in the auxv without config option
> (the config option was removed as suggested by Arjan on LKML).

One ought to cc: the /dev/random maintainer.

> /*
> + * get_random_long() returns a randomized unsigned long word.
> + * It recycles it's entropy cache for a given time period and
> + * uses half_md4_transform to generate a unique return value.
> + * Every REKEY_INTERVAL the cache is reloaded with fresh
> + * randomization data using get_random_bytes().
> + * This function is not intended for strong cryptographic routines.
> + */

What's the point of this?

--
Mathematics is the supreme nostalgia of our time.

2007-06-24 17:45:40

[permalink] [raw]

Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

diff -Nru linux-2.6.21.5.ORIG/arch/i386/kernel/process.c linux-2.6.21.5/arch/i386/kernel/process.c
--- linux-2.6.21.5.ORIG/arch/i386/kernel/process.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/i386/kernel/process.c 2007-06-24 19:00:15.000000000 +0200
@@ -924,6 +924,6 @@
unsigned long arch_align_stack(unsigned long sp)
{
if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
- sp -= get_random_int() % 8192;
+ sp -= get_random_long() % 8192;
return sp & ~0xf;
}
diff -Nru linux-2.6.21.5.ORIG/arch/i386/mm/mmap.c linux-2.6.21.5/arch/i386/mm/mmap.c
--- linux-2.6.21.5.ORIG/arch/i386/mm/mmap.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/i386/mm/mmap.c 2007-06-24 19:00:53.000000000 +0200
@@ -42,7 +42,7 @@
unsigned long random_factor = 0;

if (current->flags & PF_RANDOMIZE)
- random_factor = get_random_int() % (1024*1024);
+ random_factor = get_random_long() % (1024*1024);

if (gap < MIN_GAP)
gap = MIN_GAP;
diff -Nru linux-2.6.21.5.ORIG/arch/sparc64/kernel/sys_sparc.c linux-2.6.21.5/arch/sparc64/kernel/sys_sparc.c
--- linux-2.6.21.5.ORIG/arch/sparc64/kernel/sys_sparc.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/sparc64/kernel/sys_sparc.c 2007-06-24 19:01:44.000000000 +0200
@@ -362,7 +362,7 @@
unsigned long random_factor = 0UL;

if (current->flags & PF_RANDOMIZE) {
- random_factor = get_random_int();
+ random_factor = get_random_long();
if (test_thread_flag(TIF_32BIT))
random_factor &= ((1 * 1024 * 1024) - 1);
else
diff -Nru linux-2.6.21.5.ORIG/arch/um/kernel/process.c linux-2.6.21.5/arch/um/kernel/process.c
--- linux-2.6.21.5.ORIG/arch/um/kernel/process.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/um/kernel/process.c 2007-06-24 19:02:08.000000000 +0200
@@ -478,7 +478,7 @@
unsigned long arch_align_stack(unsigned long sp)
{
if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
- sp -= get_random_int() % 8192;
+ sp -= get_random_long() % 8192;
return sp & ~0xf;
}
#endif
diff -Nru linux-2.6.21.5.ORIG/arch/x86_64/ia32/mmap32.c linux-2.6.21.5/arch/x86_64/ia32/mmap32.c
--- linux-2.6.21.5.ORIG/arch/x86_64/ia32/mmap32.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/x86_64/ia32/mmap32.c 2007-06-24 19:02:34.000000000 +0200
@@ -44,7 +44,7 @@
unsigned long random_factor = 0;

if (current->flags & PF_RANDOMIZE)
- random_factor = get_random_int() % (1024*1024);
+ random_factor = get_random_long() % (1024*1024);

if (gap < MIN_GAP)
gap = MIN_GAP;
diff -Nru linux-2.6.21.5.ORIG/arch/x86_64/kernel/functionlist linux-2.6.21.5/arch/x86_64/kernel/functionlist
--- linux-2.6.21.5.ORIG/arch/x86_64/kernel/functionlist 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/x86_64/kernel/functionlist 2007-06-24 19:02:48.000000000 +0200
@@ -862,7 +862,7 @@
*(.text.__ide_dma_end)
*(.text.hrtimer_get_remaining)
*(.text.get_task_mm)
-*(.text.get_random_int)
+*(.text.get_random_long)
*(.text.free_pipe_info)
*(.text.filemap_write_and_wait_range)
*(.text.exit_thread)
diff -Nru linux-2.6.21.5.ORIG/arch/x86_64/kernel/process.c linux-2.6.21.5/arch/x86_64/kernel/process.c
--- linux-2.6.21.5.ORIG/arch/x86_64/kernel/process.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/x86_64/kernel/process.c 2007-06-24 19:03:02.000000000 +0200
@@ -885,6 +885,6 @@
unsigned long arch_align_stack(unsigned long sp)
{
if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
- sp -= get_random_int() % 8192;
+ sp -= get_random_long() % 8192;
return sp & ~0xf;
}
diff -Nru linux-2.6.21.5.ORIG/arch/x86_64/mm/mmap.c linux-2.6.21.5/arch/x86_64/mm/mmap.c
--- linux-2.6.21.5.ORIG/arch/x86_64/mm/mmap.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/arch/x86_64/mm/mmap.c 2007-06-24 19:03:47.000000000 +0200
@@ -18,9 +18,9 @@
if (current->flags & PF_RANDOMIZE) {
/* Add 28bit randomness which is about 40bits of address space
because mmap base has to be page aligned.
- or ~1/128 of the total user VM
- (total user address space is 47bits) */
- unsigned rnd = get_random_int() & 0xfffffff;
+ or ~1/128 of the total user VM
+ (total user address space is 47bits) */
+ unsigned rnd = get_random_long() & 0xfffffff;
mm->mmap_base += ((unsigned long)rnd) << PAGE_SHIFT;
}
mm->get_unmapped_area = arch_get_unmapped_area;
diff -Nru linux-2.6.21.5.ORIG/drivers/char/random.c linux-2.6.21.5/drivers/char/random.c
--- linux-2.6.21.5.ORIG/drivers/char/random.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/drivers/char/random.c 2007-06-24 19:04:03.000000000 +0200
@@ -437,6 +437,9 @@
.pool = nonblocking_pool_data
};

+static u32 entropycache_shared[8] __read_mostly;
+static DEFINE_PER_CPU(unsigned long , entropycache_pcpu)[16 / sizeof(unsigned long)];
+
/*
* This function adds a byte into the entropy "pool". It does not
* update the entropy estimate. The caller should call
@@ -1455,6 +1458,10 @@
keyptr->count = (ip_cnt & COUNT_MASK) << HASH_BITS;
smp_wmb();
ip_cnt++;
+
+ /* initialize the shared part of the entropy cache */
+ get_random_bytes(entropycache_shared, sizeof(entropycache_shared));
+
schedule_delayed_work(&rekey_work, REKEY_INTERVAL);
}

@@ -1637,20 +1644,17 @@

/*
- * Get a random word for internal kernel use only. Similar to urandom but
- * with the goal of minimal entropy pool depletion. As a result, the random
- * value is not cryptographically secure but for several uses the cost of
- * depleting entropy is too high
+ * get_random_long() returns a randomized unsigned long word.
+ * The entropy cache is refreshed periodically in rekey_seq_generator.
+ * This function uses half_md4_transform to generate a unique return value
+ * and is not intended for strong cryptographic routines.
*/
-unsigned int get_random_int(void)
+unsigned long get_random_long(void)
{
- /*
- * Use IP's RNG. It suits our purpose perfectly: it re-keys itself
- * every second, from the entropy pool (and thus creates a limited
- * drain on it), and uses halfMD4Transform within the second. We
- * also mix it with jiffies and the PID:
- */
- return secure_ip_id((__force __be32)(current->pid + jiffies));
+ half_md4_transform((u32 *)__get_cpu_var(entropycache_pcpu),
+ entropycache_shared);
+
+ return __get_cpu_var(entropycache_pcpu)[0];
}

/*
@@ -1669,5 +1673,5 @@

if (end <= start + len)
return 0;
- return PAGE_ALIGN(get_random_int() % range + start);
+ return PAGE_ALIGN(get_random_long() % range + start);
}
diff -Nru linux-2.6.21.5.ORIG/fs/binfmt_elf.c linux-2.6.21.5/fs/binfmt_elf.c
--- linux-2.6.21.5.ORIG/fs/binfmt_elf.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/fs/binfmt_elf.c 2007-06-24 19:04:24.000000000 +0200
@@ -200,7 +200,8 @@
NEW_AUX_ENT(AT_EUID, tsk->euid);
NEW_AUX_ENT(AT_GID, tsk->gid);
NEW_AUX_ENT(AT_EGID, tsk->egid);
- NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ NEW_AUX_ENT(AT_SECURE, security_bprm_secureexec(bprm));
+ NEW_AUX_ENT(AT_ENTROPY, get_random_long());
if (k_platform) {
NEW_AUX_ENT(AT_PLATFORM,
(elf_addr_t)(unsigned long)u_platform);
@@ -516,7 +517,7 @@

if ((current->flags & PF_RANDOMIZE) &&
!(current->personality & ADDR_NO_RANDOMIZE)) {
- random_variable = get_random_int() & STACK_RND_MASK;
+ random_variable = get_random_long() & STACK_RND_MASK;
random_variable <<= PAGE_SHIFT;
}
#ifdef CONFIG_STACK_GROWSUP
diff -Nru linux-2.6.21.5.ORIG/include/linux/auxvec.h linux-2.6.21.5/include/linux/auxvec.h
--- linux-2.6.21.5.ORIG/include/linux/auxvec.h 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/include/linux/auxvec.h 2007-06-24 17:39:12.000000000 +0200
@@ -24,8 +24,9 @@
#define AT_HWCAP 16 /* arch dependent hints at CPU capabilities */
#define AT_CLKTCK 17 /* frequency at which times() increments */

-#define AT_SECURE 23 /* secure mode boolean */
+#define AT_SECURE 23 /* secure mode boolean */
+#define AT_ENTROPY 24 /* kernel entropy in auxv */

-#define AT_VECTOR_SIZE 44 /* Size of auxiliary table. */
+#define AT_VECTOR_SIZE 45 /* Size of auxiliary table. */

#endif /* _LINUX_AUXVEC_H */
diff -Nru linux-2.6.21.5.ORIG/include/linux/random.h linux-2.6.21.5/include/linux/random.h
--- linux-2.6.21.5.ORIG/include/linux/random.h 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/include/linux/random.h 2007-06-24 18:19:54.000000000 +0200
@@ -66,7 +66,7 @@
extern const struct file_operations random_fops, urandom_fops;
#endif

-unsigned int get_random_int(void);
+unsigned long get_random_long(void);
unsigned long randomize_range(unsigned long start, unsigned long end, unsigned long len);

u32 random32(void);
diff -Nru linux-2.6.21.5.ORIG/kernel/fork.c linux-2.6.21.5/kernel/fork.c
--- linux-2.6.21.5.ORIG/kernel/fork.c 2007-06-11 20:37:06.000000000 +0200
+++ linux-2.6.21.5/kernel/fork.c 2007-06-24 19:05:00.000000000 +0200
@@ -180,7 +180,7 @@
setup_thread_stack(tsk, orig);

#ifdef CONFIG_CC_STACKPROTECTOR
- tsk->stack_canary = get_random_int();
+ tsk->stack_canary = get_random_long();
#endif

/* One for us, one for whoever does the "release_task()" (usually parent) */

Attachments:

linux-2.6.21.5-get_random_long-AT_ENTROPY.patch (8.93 kB)

2007-06-25 03:45:37

[permalink] [raw]

Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Sun, Jun 24, 2007 at 07:45:04PM +0200, Alexander Gabert wrote:
> Hi Linus,
> hi LKML,
>
> i would like to thank LKML and especially Eric (thanks for the per_cpu
> macro tips and design guidelines!) and the other contributors to this idea.
>
> This time the patch is rather big because it also removes
> get_random_int() and introduces get_random_long() throughout the kernel.

Stop right there. You still haven't answered my original question.
What is the point of this exercise in the first place, please?

Am I right in thinking you have three unrelated patches here?

- something to do with aux vector headers
- something to do with get_random_int repeating itself
- sweeping change of get_random_int to get_random_long for no obvious reason

These should be three completely separate patches.

> My findings with get_random_int was that when i called it two times very
> fast after another because of setting up two SSP randomized guard values
> for the same process, it returned the same, yet randomized, integer number.

Send me a patch that fixes the above and nothing else, please.

Then we can talk about another patch to change things to get_random_long.

> --- linux-2.6.21.5.ORIG/arch/sparc64/kernel/sys_sparc.c 2007-06-11
> 20:37:06.000000000 +0200
> +++ linux-2.6.21.5/arch/sparc64/kernel/sys_sparc.c 2007-06-24
> 19:01:44.000000000 +0200
> @@ -362,7 +362,7 @@
> unsigned long random_factor = 0UL;
>
> if (current->flags & PF_RANDOMIZE) {
> - random_factor = get_random_int();
> + random_factor = get_random_long();

This probably breaks Sparc64.

--
Mathematics is the supreme nostalgia of our time.

2007-06-25 04:43:44

[permalink] [raw]

Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Sun, 2007-06-24 at 22:45 -0500, Matt Mackall wrote:
> On Sun, Jun 24, 2007 at 07:45:04PM +0200, Alexander Gabert wrote:
> > Hi Linus,
> > hi LKML,
> >
> > i would like to thank LKML and especially Eric (thanks for the per_cpu
> > macro tips and design guidelines!) and the other contributors to this idea.
> >
> > This time the patch is rather big because it also removes
> > get_random_int() and introduces get_random_long() throughout the kernel.
>
> Stop right there. You still haven't answered my original question.
> What is the point of this exercise in the first place, please?
>
> Am I right in thinking you have three unrelated patches here?
>
> - something to do with aux vector headers

the primary goal is to pass a random value to userspace at process
start; this to save glibc from having to open /dev/urandom on ever
program start (which it does now for all apps compiled with
-fstack-protector, which in various distros is "everything").

> - sweeping change of get_random_int to get_random_long for no obvious reason

and this is because Alexander wants 2 and not 1 random int to be passed
for his own glibc proposed change (combined with get_random_int() being
designed for only 4 bytes per process ;-)

--
if you want to mail me at work (you don't), use arjan (at) linux.intel.com
Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org

2007-06-25 05:12:39

[permalink] [raw]

Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Sun, Jun 24, 2007 at 09:43:03PM -0700, Arjan van de Ven wrote:
> On Sun, 2007-06-24 at 22:45 -0500, Matt Mackall wrote:
> > On Sun, Jun 24, 2007 at 07:45:04PM +0200, Alexander Gabert wrote:
> > > Hi Linus,
> > > hi LKML,
> > >
> > > i would like to thank LKML and especially Eric (thanks for the per_cpu
> > > macro tips and design guidelines!) and the other contributors to this idea.
> > >
> > > This time the patch is rather big because it also removes
> > > get_random_int() and introduces get_random_long() throughout the kernel.
> >
> > Stop right there. You still haven't answered my original question.
> > What is the point of this exercise in the first place, please?
> >
> > Am I right in thinking you have three unrelated patches here?
> >
> > - something to do with aux vector headers
>
> the primary goal is to pass a random value to userspace at process
> start; this to save glibc from having to open /dev/urandom on ever
> program start (which it does now for all apps compiled with
> -fstack-protector, which in various distros is "everything").

Interesting.

What are our requirements here? Defending against local attackers who
can build exploits on the fly probably means something stronger than get_random_int.

> > - sweeping change of get_random_int to get_random_long for no obvious reason
>
> and this is because Alexander wants 2 and not 1 random int to be passed
> for his own glibc proposed change (combined with get_random_int() being
> designed for only 4 bytes per process ;-)

Sure. Still, separate patches.

--
Mathematics is the supreme nostalgia of our time.

2007-06-25 07:10:03

by Jakub Jelinek

[permalink] [raw]

Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

On Sun, Jun 24, 2007 at 09:43:03PM -0700, Arjan van de Ven wrote:
> > - something to do with aux vector headers
>
> the primary goal is to pass a random value to userspace at process
> start; this to save glibc from having to open /dev/urandom on ever
> program start (which it does now for all apps compiled with
> -fstack-protector, which in various distros is "everything").

There are 2 ways to compile -fstack-protector supporting glibc actually,
only one opens /dev/urandom on every program initialization, the other
computes the stack guard from some bits of the stack address (so indirectly
depends on get_random_int() in stack randomization).
Nevertheless, having one random long (32-bit for 32-bit arches, 64-bit
otherwise) in aux vector would be useful.

Jakub

2007-06-25 15:02:17

[permalink] [raw]

Subject: Re: [PATCH] get_random_long() and AT_ENTROPY for auxv, kernel 2.6.21.5

Hi Matt,
sorry for not answering your questions in the first place, i hope this
did not mean to make a bad impression
Matt Mackall schrieb:
> On Sun, Jun 24, 2007 at 07:45:04PM +0200, Alexander Gabert wrote:
>
>> Hi Linus,
>> hi LKML,
>>
>> i would like to thank LKML and especially Eric (thanks for the per_cpu
>> macro tips and design guidelines!) and the other contributors to this idea.
>>
>> This time the patch is rather big because it also removes
>> get_random_int() and introduces get_random_long() throughout the kernel.
>>
>
> Stop right there. You still haven't answered my original question.
> What is the point of this exercise in the first place, please?
>
> Am I right in thinking you have three unrelated patches here?
>
I don't think so but you may be right nonetheless if my opinion.
> - something to do with aux vector headers
>
Adding the new field
> - something to do with get_random_int repeating itself
>
Found while adding the new field and testing it.
> - sweeping change of get_random_int to get_random_long for no obvious reason
>
It is needed for properly initializing a SSP guard which is (afaik) a
long value.
> These should be three completely separate patches.
>
Probably ... but bear in mind that the goal is still the same: allowing
glibc to use SSP with /proc/self/auxv instead of fopen(/dev/urandom) as
it is now.
Effectively saving three syscalls (open,read,close) and making life
easier for glibc because randomization "generated" in the kernel does
not deplete /dev/urandom too much for high coverage SSP userlands (i.e.
Gentoo Hardened).

I can imagine that Redhat would do the same with the SSP implementation
in glibc, i think if this patch moves into kernel, they will bring out a
glibc patch that is checking for AT_ENTROPY and using the opening of
/dev/urandom for retrieving randomized data as a fallback for machines
where such a kernel is not available. This is a win-win situation for
both sides- the kernel wins because the pressure on /dev/urandom is
released a bit (applicable to SSP environments) and the glibc wins
because it has a reliable, fast, cheap and easy to use source for
randomization.

Thank you,

Alex

2007-06-25 15:20:39