Jon noticed that I had a typo in my _ASM_KPROBE_ERROR_INJECT macro. I went to
figure out why the compiler didn't catch it and it's because it was not used
anywhere. I had copied it from the trace blacklist code without understanding
where it was used as cscope didn't find the original macro I was looking for, so
I assumed it was some voodoo and left it in place. Turns out cscope failed me
and I didn't need the macro at all, the trace blacklist thing I was looking at
was for marking assembly functions as blacklisted and I have no intention of
marking assembly functions as error injectable at the moment.
v7->v8:
- removed the _ASM_KPROBE_ERROR_INJECT since it was not needed.
v6->v7:
- moved the opt-in macro to bpf.h out of kprobes.h.
v5->v6:
- add BPF_ALLOW_ERROR_INJECTION() tagging for functions that will support this
feature. This way only functions that opt-in will be allowed to be
overridden.
- added a btrfs patch to allow error injection for open_ctree() so that the bpf
sample actually works.
v4->v5:
- disallow kprobe_override programs from being put in the prog map array so we
don't tail call into something we didn't check. This allows us to make the
normal path still fast without a bunch of percpu operations.
v3->v4:
- fix a build error found by kbuild test bot (I didn't wait long enough
apparently.)
- Added a warning message as per Daniels suggestion.
v2->v3:
- added a ->kprobe_override flag to bpf_prog.
- added some sanity checks to disallow attaching bpf progs that have
->kprobe_override set that aren't for ftrace kprobes.
- added the trace_kprobe_ftrace helper to check if the trace_event_call is a
ftrace kprobe.
- renamed bpf_kprobe_state to bpf_kprobe_override, fixed it so we only read this
value in the kprobe path, and thus only write to it if we're overriding or
clearing the override.
v1->v2:
- moved things around to make sure that bpf_override_return could really only be
used for an ftrace kprobe.
- killed the special return values from trace_call_bpf.
- renamed pc_modified to bpf_kprobe_state so bpf_override_return could tell if
it was being called from an ftrace kprobe context.
- reworked the logic in kprobe_perf_func to take advantage of bpf_kprobe_state.
- updated the test as per Alexei's review.
- Original message -
A lot of our error paths are not well tested because we have no good way of
injecting errors generically. Some subystems (block, memory) have ways to
inject errors, but they are random so it's hard to get reproduceable results.
With BPF we can add determinism to our error injection. We can use kprobes and
other things to verify we are injecting errors at the exact case we are trying
to test. This patch gives us the tool to actual do the error injection part.
It is very simple, we just set the return value of the pt_regs we're given to
whatever we provide, and then override the PC with a dummy function that simply
returns.
Right now this only works on x86, but it would be simple enough to expand to
other architectures. Thanks,
Josef
From: Josef Bacik <[email protected]>
This allows us to do error injection with BPF for open_ctree.
Signed-off-by: Josef Bacik <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
---
fs/btrfs/disk-io.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index dfdab849037b..69d17a640b94 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -30,6 +30,7 @@
#include <linux/ratelimit.h>
#include <linux/uuid.h>
#include <linux/semaphore.h>
+#include <linux/bpf.h>
#include <asm/unaligned.h>
#include "ctree.h"
#include "disk-io.h"
@@ -3283,6 +3284,7 @@ int open_ctree(struct super_block *sb,
goto fail_block_groups;
goto retry_root_backup;
}
+BPF_ALLOW_ERROR_INJECTION(open_ctree);
static void btrfs_end_buffer_write_sync(struct buffer_head *bh, int uptodate)
{
--
2.7.5
From: Josef Bacik <[email protected]>
Using BPF we can override kprob'ed functions and return arbitrary
values. Obviously this can be a bit unsafe, so make this feature opt-in
for functions. Simply tag a function with KPROBE_ERROR_INJECT_SYMBOL in
order to give BPF access to that function for error injection purposes.
Signed-off-by: Josef Bacik <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
---
include/asm-generic/vmlinux.lds.h | 10 +++
include/linux/bpf.h | 11 +++
include/linux/kprobes.h | 1 +
include/linux/module.h | 5 ++
kernel/kprobes.c | 163 ++++++++++++++++++++++++++++++++++++++
kernel/module.c | 6 +-
6 files changed, 195 insertions(+), 1 deletion(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8acfc1e099e1..85822804861e 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -136,6 +136,15 @@
#define KPROBE_BLACKLIST()
#endif
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+#define ERROR_INJECT_LIST() . = ALIGN(8); \
+ VMLINUX_SYMBOL(__start_kprobe_error_inject_list) = .; \
+ KEEP(*(_kprobe_error_inject_list)) \
+ VMLINUX_SYMBOL(__stop_kprobe_error_inject_list) = .;
+#else
+#define ERROR_INJECT_LIST()
+#endif
+
#ifdef CONFIG_EVENT_TRACING
#define FTRACE_EVENTS() . = ALIGN(8); \
VMLINUX_SYMBOL(__start_ftrace_events) = .; \
@@ -560,6 +569,7 @@
FTRACE_EVENTS() \
TRACE_SYSCALLS() \
KPROBE_BLACKLIST() \
+ ERROR_INJECT_LIST() \
MEM_DISCARD(init.rodata) \
CLK_OF_TABLES() \
RESERVEDMEM_OF_TABLES() \
diff --git a/include/linux/bpf.h b/include/linux/bpf.h
index 520aeebe0d93..552a666a338b 100644
--- a/include/linux/bpf.h
+++ b/include/linux/bpf.h
@@ -530,4 +530,15 @@ extern const struct bpf_func_proto bpf_sock_map_update_proto;
void bpf_user_rnd_init_once(void);
u64 bpf_user_rnd_u32(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
+#if defined(__KERNEL__) && !defined(__ASSEMBLY__)
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+#define BPF_ALLOW_ERROR_INJECTION(fname) \
+static unsigned long __used \
+ __attribute__((__section__("_kprobe_error_inject_list"))) \
+ _eil_addr_##fname = (unsigned long)fname;
+#else
+#define BPF_ALLOW_ERROR_INJECTION(fname)
+#endif
+#endif
+
#endif /* _LINUX_BPF_H */
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index bd2684700b74..4f501cb73aec 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -271,6 +271,7 @@ extern bool arch_kprobe_on_func_entry(unsigned long offset);
extern bool kprobe_on_func_entry(kprobe_opcode_t *addr, const char *sym, unsigned long offset);
extern bool within_kprobe_blacklist(unsigned long addr);
+extern bool within_kprobe_error_injection_list(unsigned long addr);
struct kprobe_insn_cache {
struct mutex mutex;
diff --git a/include/linux/module.h b/include/linux/module.h
index fe5aa3736707..7bb1a9b9a322 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h
@@ -475,6 +475,11 @@ struct module {
ctor_fn_t *ctors;
unsigned int num_ctors;
#endif
+
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+ unsigned int num_kprobe_ei_funcs;
+ unsigned long *kprobe_ei_funcs;
+#endif
} ____cacheline_aligned __randomize_layout;
#ifndef MODULE_ARCH_INIT
#define MODULE_ARCH_INIT {}
diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index a1606a4224e1..bdd7dd724f6f 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -83,6 +83,16 @@ static raw_spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
return &(kretprobe_table_locks[hash].lock);
}
+/* List of symbols that can be overriden for error injection. */
+static LIST_HEAD(kprobe_error_injection_list);
+static DEFINE_MUTEX(kprobe_ei_mutex);
+struct kprobe_ei_entry {
+ struct list_head list;
+ unsigned long start_addr;
+ unsigned long end_addr;
+ void *priv;
+};
+
/* Blacklist -- list of struct kprobe_blacklist_entry */
static LIST_HEAD(kprobe_blacklist);
@@ -1392,6 +1402,17 @@ bool within_kprobe_blacklist(unsigned long addr)
return false;
}
+bool within_kprobe_error_injection_list(unsigned long addr)
+{
+ struct kprobe_ei_entry *ent;
+
+ list_for_each_entry(ent, &kprobe_error_injection_list, list) {
+ if (addr >= ent->start_addr && addr < ent->end_addr)
+ return true;
+ }
+ return false;
+}
+
/*
* If we have a symbol_name argument, look it up and add the offset field
* to it. This way, we can specify a relative address to a symbol.
@@ -2164,6 +2185,86 @@ static int __init populate_kprobe_blacklist(unsigned long *start,
return 0;
}
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+/* Markers of the _kprobe_error_inject_list section */
+extern unsigned long __start_kprobe_error_inject_list[];
+extern unsigned long __stop_kprobe_error_inject_list[];
+
+/*
+ * Lookup and populate the kprobe_error_injection_list.
+ *
+ * For safety reasons we only allow certain functions to be overriden with
+ * bpf_error_injection, so we need to populate the list of the symbols that have
+ * been marked as safe for overriding.
+ */
+static void populate_kprobe_error_injection_list(unsigned long *start,
+ unsigned long *end,
+ void *priv)
+{
+ unsigned long *iter;
+ struct kprobe_ei_entry *ent;
+ unsigned long entry, offset = 0, size = 0;
+
+ mutex_lock(&kprobe_ei_mutex);
+ for (iter = start; iter < end; iter++) {
+ entry = arch_deref_entry_point((void *)*iter);
+
+ if (!kernel_text_address(entry) ||
+ !kallsyms_lookup_size_offset(entry, &size, &offset)) {
+ pr_err("Failed to find error inject entry at %p\n",
+ (void *)entry);
+ continue;
+ }
+
+ ent = kmalloc(sizeof(*ent), GFP_KERNEL);
+ if (!ent)
+ break;
+ ent->start_addr = entry;
+ ent->end_addr = entry + size;
+ ent->priv = priv;
+ INIT_LIST_HEAD(&ent->list);
+ list_add_tail(&ent->list, &kprobe_error_injection_list);
+ }
+ mutex_unlock(&kprobe_ei_mutex);
+}
+
+static void __init populate_kernel_kprobe_ei_list(void)
+{
+ populate_kprobe_error_injection_list(__start_kprobe_error_inject_list,
+ __stop_kprobe_error_inject_list,
+ NULL);
+}
+
+static void module_load_kprobe_ei_list(struct module *mod)
+{
+ if (!mod->num_kprobe_ei_funcs)
+ return;
+ populate_kprobe_error_injection_list(mod->kprobe_ei_funcs,
+ mod->kprobe_ei_funcs +
+ mod->num_kprobe_ei_funcs, mod);
+}
+
+static void module_unload_kprobe_ei_list(struct module *mod)
+{
+ struct kprobe_ei_entry *ent, *n;
+ if (!mod->num_kprobe_ei_funcs)
+ return;
+
+ mutex_lock(&kprobe_ei_mutex);
+ list_for_each_entry_safe(ent, n, &kprobe_error_injection_list, list) {
+ if (ent->priv == mod) {
+ list_del_init(&ent->list);
+ kfree(ent);
+ }
+ }
+ mutex_unlock(&kprobe_ei_mutex);
+}
+#else
+static inline void __init populate_kernel_kprobe_ei_list(void) {}
+static inline void module_load_kprobe_ei_list(struct module *m) {}
+static inline void module_unload_kprobe_ei_list(struct module *m) {}
+#endif
+
/* Module notifier call back, checking kprobes on the module */
static int kprobes_module_callback(struct notifier_block *nb,
unsigned long val, void *data)
@@ -2174,6 +2275,11 @@ static int kprobes_module_callback(struct notifier_block *nb,
unsigned int i;
int checkcore = (val == MODULE_STATE_GOING);
+ if (val == MODULE_STATE_COMING)
+ module_load_kprobe_ei_list(mod);
+ else if (val == MODULE_STATE_GOING)
+ module_unload_kprobe_ei_list(mod);
+
if (val != MODULE_STATE_GOING && val != MODULE_STATE_LIVE)
return NOTIFY_DONE;
@@ -2236,6 +2342,8 @@ static int __init init_kprobes(void)
pr_err("Please take care of using kprobes.\n");
}
+ populate_kernel_kprobe_ei_list();
+
if (kretprobe_blacklist_size) {
/* lookup the function address from its name */
for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
@@ -2403,6 +2511,56 @@ static const struct file_operations debugfs_kprobe_blacklist_ops = {
.release = seq_release,
};
+/*
+ * kprobes/error_injection_list -- shows which functions can be overriden for
+ * error injection.
+ * */
+static void *kprobe_ei_seq_start(struct seq_file *m, loff_t *pos)
+{
+ mutex_lock(&kprobe_ei_mutex);
+ return seq_list_start(&kprobe_error_injection_list, *pos);
+}
+
+static void kprobe_ei_seq_stop(struct seq_file *m, void *v)
+{
+ mutex_unlock(&kprobe_ei_mutex);
+}
+
+static void *kprobe_ei_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+ return seq_list_next(v, &kprobe_error_injection_list, pos);
+}
+
+static int kprobe_ei_seq_show(struct seq_file *m, void *v)
+{
+ char buffer[KSYM_SYMBOL_LEN];
+ struct kprobe_ei_entry *ent =
+ list_entry(v, struct kprobe_ei_entry, list);
+
+ sprint_symbol(buffer, ent->start_addr);
+ seq_printf(m, "%s\n", buffer);
+ return 0;
+}
+
+static const struct seq_operations kprobe_ei_seq_ops = {
+ .start = kprobe_ei_seq_start,
+ .next = kprobe_ei_seq_next,
+ .stop = kprobe_ei_seq_stop,
+ .show = kprobe_ei_seq_show,
+};
+
+static int kprobe_ei_open(struct inode *inode, struct file *filp)
+{
+ return seq_open(filp, &kprobe_ei_seq_ops);
+}
+
+static const struct file_operations debugfs_kprobe_ei_ops = {
+ .open = kprobe_ei_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
static void arm_all_kprobes(void)
{
struct hlist_head *head;
@@ -2544,6 +2702,11 @@ static int __init debugfs_kprobe_init(void)
if (!file)
goto error;
+ file = debugfs_create_file("error_injection_list", 0444, dir, NULL,
+ &debugfs_kprobe_ei_ops);
+ if (!file)
+ goto error;
+
return 0;
error:
diff --git a/kernel/module.c b/kernel/module.c
index de66ec825992..19d8d9455f2f 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3110,7 +3110,11 @@ static int find_module_sections(struct module *mod, struct load_info *info)
sizeof(*mod->ftrace_callsites),
&mod->num_ftrace_callsites);
#endif
-
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+ mod->kprobe_ei_funcs = section_objs(info, "_kprobe_error_inject_list",
+ sizeof(*mod->kprobe_ei_funcs),
+ &mod->num_kprobe_ei_funcs);
+#endif
mod->extable = section_objs(info, "__ex_table",
sizeof(*mod->extable), &mod->num_exentries);
--
2.7.5
From: Josef Bacik <[email protected]>
This was instrumental in reproducing a space cache bug.
Signed-off-by: Josef Bacik <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
---
fs/btrfs/free-space-cache.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
index cdc9f4015ec3..daa98dc1f844 100644
--- a/fs/btrfs/free-space-cache.c
+++ b/fs/btrfs/free-space-cache.c
@@ -22,6 +22,7 @@
#include <linux/slab.h>
#include <linux/math64.h>
#include <linux/ratelimit.h>
+#include <linux/bpf.h>
#include "ctree.h"
#include "free-space-cache.h"
#include "transaction.h"
@@ -332,6 +333,7 @@ static int io_ctl_init(struct btrfs_io_ctl *io_ctl, struct inode *inode,
return 0;
}
+BPF_ALLOW_ERROR_INJECTION(io_ctl_init);
static void io_ctl_free(struct btrfs_io_ctl *io_ctl)
{
--
2.7.5
From: Josef Bacik <[email protected]>
This adds a basic test for bpf_override_return to verify it works. We
override the main function for mounting a btrfs fs so it'll return
-ENOMEM and then make sure that trying to mount a btrfs fs will fail.
Acked-by: Alexei Starovoitov <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
---
samples/bpf/Makefile | 4 ++++
samples/bpf/test_override_return.sh | 15 +++++++++++++++
samples/bpf/tracex7_kern.c | 16 ++++++++++++++++
samples/bpf/tracex7_user.c | 28 ++++++++++++++++++++++++++++
tools/include/uapi/linux/bpf.h | 7 ++++++-
tools/testing/selftests/bpf/bpf_helpers.h | 3 ++-
6 files changed, 71 insertions(+), 2 deletions(-)
create mode 100755 samples/bpf/test_override_return.sh
create mode 100644 samples/bpf/tracex7_kern.c
create mode 100644 samples/bpf/tracex7_user.c
diff --git a/samples/bpf/Makefile b/samples/bpf/Makefile
index ea2b9e6135f3..83d06bc1f710 100644
--- a/samples/bpf/Makefile
+++ b/samples/bpf/Makefile
@@ -14,6 +14,7 @@ hostprogs-y += tracex3
hostprogs-y += tracex4
hostprogs-y += tracex5
hostprogs-y += tracex6
+hostprogs-y += tracex7
hostprogs-y += test_probe_write_user
hostprogs-y += trace_output
hostprogs-y += lathist
@@ -58,6 +59,7 @@ tracex3-objs := bpf_load.o $(LIBBPF) tracex3_user.o
tracex4-objs := bpf_load.o $(LIBBPF) tracex4_user.o
tracex5-objs := bpf_load.o $(LIBBPF) tracex5_user.o
tracex6-objs := bpf_load.o $(LIBBPF) tracex6_user.o
+tracex7-objs := bpf_load.o $(LIBBPF) tracex7_user.o
load_sock_ops-objs := bpf_load.o $(LIBBPF) load_sock_ops.o
test_probe_write_user-objs := bpf_load.o $(LIBBPF) test_probe_write_user_user.o
trace_output-objs := bpf_load.o $(LIBBPF) trace_output_user.o
@@ -100,6 +102,7 @@ always += tracex3_kern.o
always += tracex4_kern.o
always += tracex5_kern.o
always += tracex6_kern.o
+always += tracex7_kern.o
always += sock_flags_kern.o
always += test_probe_write_user_kern.o
always += trace_output_kern.o
@@ -153,6 +156,7 @@ HOSTLOADLIBES_tracex3 += -lelf
HOSTLOADLIBES_tracex4 += -lelf -lrt
HOSTLOADLIBES_tracex5 += -lelf
HOSTLOADLIBES_tracex6 += -lelf
+HOSTLOADLIBES_tracex7 += -lelf
HOSTLOADLIBES_test_cgrp2_sock2 += -lelf
HOSTLOADLIBES_load_sock_ops += -lelf
HOSTLOADLIBES_test_probe_write_user += -lelf
diff --git a/samples/bpf/test_override_return.sh b/samples/bpf/test_override_return.sh
new file mode 100755
index 000000000000..e68b9ee6814b
--- /dev/null
+++ b/samples/bpf/test_override_return.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+
+rm -f testfile.img
+dd if=/dev/zero of=testfile.img bs=1M seek=1000 count=1
+DEVICE=$(losetup --show -f testfile.img)
+mkfs.btrfs -f $DEVICE
+mkdir tmpmnt
+./tracex7 $DEVICE
+if [ $? -eq 0 ]
+then
+ echo "SUCCESS!"
+else
+ echo "FAILED!"
+fi
+losetup -d $DEVICE
diff --git a/samples/bpf/tracex7_kern.c b/samples/bpf/tracex7_kern.c
new file mode 100644
index 000000000000..1ab308a43e0f
--- /dev/null
+++ b/samples/bpf/tracex7_kern.c
@@ -0,0 +1,16 @@
+#include <uapi/linux/ptrace.h>
+#include <uapi/linux/bpf.h>
+#include <linux/version.h>
+#include "bpf_helpers.h"
+
+SEC("kprobe/open_ctree")
+int bpf_prog1(struct pt_regs *ctx)
+{
+ unsigned long rc = -12;
+
+ bpf_override_return(ctx, rc);
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";
+u32 _version SEC("version") = LINUX_VERSION_CODE;
diff --git a/samples/bpf/tracex7_user.c b/samples/bpf/tracex7_user.c
new file mode 100644
index 000000000000..8a52ac492e8b
--- /dev/null
+++ b/samples/bpf/tracex7_user.c
@@ -0,0 +1,28 @@
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <linux/bpf.h>
+#include <unistd.h>
+#include "libbpf.h"
+#include "bpf_load.h"
+
+int main(int argc, char **argv)
+{
+ FILE *f;
+ char filename[256];
+ char command[256];
+ int ret;
+
+ snprintf(filename, sizeof(filename), "%s_kern.o", argv[0]);
+
+ if (load_bpf_file(filename)) {
+ printf("%s", bpf_log_buf);
+ return 1;
+ }
+
+ snprintf(command, 256, "mount %s tmpmnt/", argv[1]);
+ f = popen(command, "r");
+ ret = pclose(f);
+
+ return ret ? 0 : 1;
+}
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 4a4b6e78c977..3756dde69834 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -673,6 +673,10 @@ union bpf_attr {
* @buf: buf to fill
* @buf_size: size of the buf
* Return : 0 on success or negative error code
+ *
+ * int bpf_override_return(pt_regs, rc)
+ * @pt_regs: pointer to struct pt_regs
+ * @rc: the return value to set
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -732,7 +736,8 @@ union bpf_attr {
FN(xdp_adjust_meta), \
FN(perf_event_read_value), \
FN(perf_prog_read_value), \
- FN(getsockopt),
+ FN(getsockopt), \
+ FN(override_return),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/tools/testing/selftests/bpf/bpf_helpers.h b/tools/testing/selftests/bpf/bpf_helpers.h
index abfa4c5c8527..086733298d5e 100644
--- a/tools/testing/selftests/bpf/bpf_helpers.h
+++ b/tools/testing/selftests/bpf/bpf_helpers.h
@@ -81,7 +81,8 @@ static int (*bpf_perf_event_read_value)(void *map, unsigned long long flags,
static int (*bpf_perf_prog_read_value)(void *ctx, void *buf,
unsigned int buf_size) =
(void *) BPF_FUNC_perf_prog_read_value;
-
+static int (*bpf_override_return)(void *ctx, unsigned long rc) =
+ (void *) BPF_FUNC_override_return;
/* llvm builtin functions that eBPF C program may use to
* emit BPF_LD_ABS and BPF_LD_IND instructions
--
2.7.5
From: Josef Bacik <[email protected]>
Error injection is sloppy and very ad-hoc. BPF could fill this niche
perfectly with it's kprobe functionality. We could make sure errors are
only triggered in specific call chains that we care about with very
specific situations. Accomplish this with the bpf_override_funciton
helper. This will modify the probe'd callers return value to the
specified value and set the PC to an override function that simply
returns, bypassing the originally probed function. This gives us a nice
clean way to implement systematic error injection for all of our code
paths.
Acked-by: Alexei Starovoitov <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Signed-off-by: Josef Bacik <[email protected]>
---
arch/Kconfig | 3 +++
arch/x86/Kconfig | 1 +
arch/x86/include/asm/kprobes.h | 4 +++
arch/x86/include/asm/ptrace.h | 5 ++++
arch/x86/kernel/kprobes/ftrace.c | 14 ++++++++++
include/linux/filter.h | 3 ++-
include/linux/trace_events.h | 1 +
include/uapi/linux/bpf.h | 7 ++++-
kernel/bpf/core.c | 3 +++
kernel/bpf/verifier.c | 2 ++
kernel/events/core.c | 7 +++++
kernel/trace/Kconfig | 11 ++++++++
kernel/trace/bpf_trace.c | 38 +++++++++++++++++++++++++++
kernel/trace/trace_kprobe.c | 55 +++++++++++++++++++++++++++++++++++-----
kernel/trace/trace_probe.h | 12 +++++++++
15 files changed, 157 insertions(+), 9 deletions(-)
diff --git a/arch/Kconfig b/arch/Kconfig
index d789a89cb32c..4fb618082259 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -195,6 +195,9 @@ config HAVE_OPTPROBES
config HAVE_KPROBES_ON_FTRACE
bool
+config HAVE_KPROBE_OVERRIDE
+ bool
+
config HAVE_NMI
bool
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 971feac13506..5126d2750dd0 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -152,6 +152,7 @@ config X86
select HAVE_KERNEL_XZ
select HAVE_KPROBES
select HAVE_KPROBES_ON_FTRACE
+ select HAVE_KPROBE_OVERRIDE
select HAVE_KRETPROBES
select HAVE_KVM
select HAVE_LIVEPATCH if X86_64
diff --git a/arch/x86/include/asm/kprobes.h b/arch/x86/include/asm/kprobes.h
index 6cf65437b5e5..c6c3b1f4306a 100644
--- a/arch/x86/include/asm/kprobes.h
+++ b/arch/x86/include/asm/kprobes.h
@@ -67,6 +67,10 @@ extern const int kretprobe_blacklist_size;
void arch_remove_kprobe(struct kprobe *p);
asmlinkage void kretprobe_trampoline(void);
+#ifdef CONFIG_KPROBES_ON_FTRACE
+extern void arch_ftrace_kprobe_override_function(struct pt_regs *regs);
+#endif
+
/* Architecture specific copy of original instruction*/
struct arch_specific_insn {
/* copy of the original instruction */
diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
index 91c04c8e67fa..f04e71800c2f 100644
--- a/arch/x86/include/asm/ptrace.h
+++ b/arch/x86/include/asm/ptrace.h
@@ -108,6 +108,11 @@ static inline unsigned long regs_return_value(struct pt_regs *regs)
return regs->ax;
}
+static inline void regs_set_return_value(struct pt_regs *regs, unsigned long rc)
+{
+ regs->ax = rc;
+}
+
/*
* user_mode(regs) determines whether a register set came from user
* mode. On x86_32, this is true if V8086 mode was enabled OR if the
diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index 041f7b6dfa0f..3c455bf490cb 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -97,3 +97,17 @@ int arch_prepare_kprobe_ftrace(struct kprobe *p)
p->ainsn.boostable = false;
return 0;
}
+
+asmlinkage void override_func(void);
+asm(
+ ".type override_func, @function\n"
+ "override_func:\n"
+ " ret\n"
+ ".size override_func, .-override_func\n"
+);
+
+void arch_ftrace_kprobe_override_function(struct pt_regs *regs)
+{
+ regs->ip = (unsigned long)&override_func;
+}
+NOKPROBE_SYMBOL(arch_ftrace_kprobe_override_function);
diff --git a/include/linux/filter.h b/include/linux/filter.h
index cdd78a7beaae..dfa44fd74bae 100644
--- a/include/linux/filter.h
+++ b/include/linux/filter.h
@@ -458,7 +458,8 @@ struct bpf_prog {
locked:1, /* Program image locked? */
gpl_compatible:1, /* Is filter GPL compatible? */
cb_access:1, /* Is control block accessed? */
- dst_needed:1; /* Do we need dst entry? */
+ dst_needed:1, /* Do we need dst entry? */
+ kprobe_override:1; /* Do we override a kprobe? */
kmemcheck_bitfield_end(meta);
enum bpf_prog_type type; /* Type of BPF program */
u32 len; /* Number of filter blocks */
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
index fc6aeca945db..be8bd5a8efaa 100644
--- a/include/linux/trace_events.h
+++ b/include/linux/trace_events.h
@@ -522,6 +522,7 @@ do { \
struct perf_event;
DECLARE_PER_CPU(struct pt_regs, perf_trace_regs);
+DECLARE_PER_CPU(int, bpf_kprobe_override);
extern int perf_trace_init(struct perf_event *event);
extern void perf_trace_destroy(struct perf_event *event);
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 0b7b54d898bd..1ad5b87a42f6 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -673,6 +673,10 @@ union bpf_attr {
* @buf: buf to fill
* @buf_size: size of the buf
* Return : 0 on success or negative error code
+ *
+ * int bpf_override_return(pt_regs, rc)
+ * @pt_regs: pointer to struct pt_regs
+ * @rc: the return value to set
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@@ -732,7 +736,8 @@ union bpf_attr {
FN(xdp_adjust_meta), \
FN(perf_event_read_value), \
FN(perf_prog_read_value), \
- FN(getsockopt),
+ FN(getsockopt), \
+ FN(override_return),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
index 7fe448799d76..ee3888ed5e85 100644
--- a/kernel/bpf/core.c
+++ b/kernel/bpf/core.c
@@ -1326,6 +1326,9 @@ EVAL4(PROG_NAME_LIST, 416, 448, 480, 512)
bool bpf_prog_array_compatible(struct bpf_array *array,
const struct bpf_prog *fp)
{
+ if (fp->kprobe_override)
+ return false;
+
if (!array->owner_prog_type) {
/* There's no owner yet where we could check for
* compatibility.
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index d906775e12c1..f8f7927a9152 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -4189,6 +4189,8 @@ static int fixup_bpf_calls(struct bpf_verifier_env *env)
prog->dst_needed = 1;
if (insn->imm == BPF_FUNC_get_prandom_u32)
bpf_user_rnd_init_once();
+ if (insn->imm == BPF_FUNC_override_return)
+ prog->kprobe_override = 1;
if (insn->imm == BPF_FUNC_tail_call) {
/* If we tail call into other programs, we
* cannot make any assumptions since they can
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 9660ee65fbef..0d7fce52391d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -8169,6 +8169,13 @@ static int perf_event_set_bpf_prog(struct perf_event *event, u32 prog_fd)
return -EINVAL;
}
+ /* Kprobe override only works for kprobes, not uprobes. */
+ if (prog->kprobe_override &&
+ !(event->tp_event->flags & TRACE_EVENT_FL_KPROBE)) {
+ bpf_prog_put(prog);
+ return -EINVAL;
+ }
+
if (is_tracepoint || is_syscall_tp) {
int off = trace_event_get_offsets(event->tp_event);
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 434c840e2d82..9dc0deeaad2b 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -518,6 +518,17 @@ config FUNCTION_PROFILER
If in doubt, say N.
+config BPF_KPROBE_OVERRIDE
+ bool "Enable BPF programs to override a kprobed function"
+ depends on BPF_EVENTS
+ depends on KPROBES_ON_FTRACE
+ depends on HAVE_KPROBE_OVERRIDE
+ depends on DYNAMIC_FTRACE_WITH_REGS
+ default n
+ help
+ Allows BPF to override the execution of a probed function and
+ set a different return value. This is used for error injection.
+
config FTRACE_MCOUNT_RECORD
def_bool y
depends on DYNAMIC_FTRACE
diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index 136aa6bb0422..c6c1b3f9afd2 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -13,6 +13,10 @@
#include <linux/filter.h>
#include <linux/uaccess.h>
#include <linux/ctype.h>
+#include <linux/kprobes.h>
+#include <asm/kprobes.h>
+
+#include "trace_probe.h"
#include "trace.h"
u64 bpf_get_stackid(u64 r1, u64 r2, u64 r3, u64 r4, u64 r5);
@@ -76,6 +80,29 @@ unsigned int trace_call_bpf(struct trace_event_call *call, void *ctx)
}
EXPORT_SYMBOL_GPL(trace_call_bpf);
+#ifdef CONFIG_BPF_KPROBE_OVERRIDE
+BPF_CALL_2(bpf_override_return, struct pt_regs *, regs, unsigned long, rc)
+{
+ __this_cpu_write(bpf_kprobe_override, 1);
+ regs_set_return_value(regs, rc);
+ arch_ftrace_kprobe_override_function(regs);
+ return 0;
+}
+#else
+BPF_CALL_2(bpf_override_return, struct pt_regs *, regs, unsigned long, rc)
+{
+ return -EINVAL;
+}
+#endif
+
+static const struct bpf_func_proto bpf_override_return_proto = {
+ .func = bpf_override_return,
+ .gpl_only = true,
+ .ret_type = RET_INTEGER,
+ .arg1_type = ARG_PTR_TO_CTX,
+ .arg2_type = ARG_ANYTHING,
+};
+
BPF_CALL_3(bpf_probe_read, void *, dst, u32, size, const void *, unsafe_ptr)
{
int ret;
@@ -551,6 +578,8 @@ static const struct bpf_func_proto *kprobe_prog_func_proto(enum bpf_func_id func
return &bpf_get_stackid_proto;
case BPF_FUNC_perf_event_read_value:
return &bpf_perf_event_read_value_proto;
+ case BPF_FUNC_override_return:
+ return &bpf_override_return_proto;
default:
return tracing_func_proto(func_id);
}
@@ -766,6 +795,15 @@ int perf_event_attach_bpf_prog(struct perf_event *event,
struct bpf_prog_array *new_array;
int ret = -EEXIST;
+ /*
+ * Kprobe override only works for ftrace based kprobes, and only if they
+ * are on the opt-in list.
+ */
+ if (prog->kprobe_override &&
+ (!trace_kprobe_ftrace(event->tp_event) ||
+ !trace_kprobe_error_injectable(event->tp_event)))
+ return -EINVAL;
+
mutex_lock(&bpf_event_mutex);
if (event->prog)
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index abf92e478cfb..ad3361790392 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -42,6 +42,7 @@ struct trace_kprobe {
(offsetof(struct trace_kprobe, tp.args) + \
(sizeof(struct probe_arg) * (n)))
+DEFINE_PER_CPU(int, bpf_kprobe_override);
static nokprobe_inline bool trace_kprobe_is_return(struct trace_kprobe *tk)
{
@@ -87,6 +88,27 @@ static nokprobe_inline unsigned long trace_kprobe_nhit(struct trace_kprobe *tk)
return nhit;
}
+int trace_kprobe_ftrace(struct trace_event_call *call)
+{
+ struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
+ return kprobe_ftrace(&tk->rp.kp);
+}
+
+int trace_kprobe_error_injectable(struct trace_event_call *call)
+{
+ struct trace_kprobe *tk = (struct trace_kprobe *)call->data;
+ unsigned long addr;
+
+ if (tk->symbol) {
+ addr = (unsigned long)
+ kallsyms_lookup_name(trace_kprobe_symbol(tk));
+ addr += tk->rp.kp.offset;
+ } else {
+ addr = (unsigned long)tk->rp.kp.addr;
+ }
+ return within_kprobe_error_injection_list(addr);
+}
+
static int register_kprobe_event(struct trace_kprobe *tk);
static int unregister_kprobe_event(struct trace_kprobe *tk);
@@ -1170,7 +1192,7 @@ static int kretprobe_event_define_fields(struct trace_event_call *event_call)
#ifdef CONFIG_PERF_EVENTS
/* Kprobe profile handler */
-static void
+static int
kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
{
struct trace_event_call *call = &tk->tp.call;
@@ -1179,12 +1201,29 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
int size, __size, dsize;
int rctx;
- if (bpf_prog_array_valid(call) && !trace_call_bpf(call, regs))
- return;
+ if (bpf_prog_array_valid(call)) {
+ int ret;
+
+ ret = trace_call_bpf(call, regs);
+
+ /*
+ * We need to check and see if we modified the pc of the
+ * pt_regs, and if so clear the kprobe and return 1 so that we
+ * don't do the instruction skipping. Also reset our state so
+ * we are clean the next pass through.
+ */
+ if (__this_cpu_read(bpf_kprobe_override)) {
+ __this_cpu_write(bpf_kprobe_override, 0);
+ reset_current_kprobe();
+ return 1;
+ }
+ if (!ret)
+ return 0;
+ }
head = this_cpu_ptr(call->perf_events);
if (hlist_empty(head))
- return;
+ return 0;
dsize = __get_data_size(&tk->tp, regs);
__size = sizeof(*entry) + tk->tp.size + dsize;
@@ -1193,13 +1232,14 @@ kprobe_perf_func(struct trace_kprobe *tk, struct pt_regs *regs)
entry = perf_trace_buf_alloc(size, NULL, &rctx);
if (!entry)
- return;
+ return 0;
entry->ip = (unsigned long)tk->rp.kp.addr;
memset(&entry[1], 0, dsize);
store_trace_args(sizeof(*entry), &tk->tp, regs, (u8 *)&entry[1], dsize);
perf_trace_buf_submit(entry, size, rctx, call->event.type, 1, regs,
head, NULL, NULL);
+ return 0;
}
NOKPROBE_SYMBOL(kprobe_perf_func);
@@ -1275,6 +1315,7 @@ static int kprobe_register(struct trace_event_call *event,
static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs)
{
struct trace_kprobe *tk = container_of(kp, struct trace_kprobe, rp.kp);
+ int ret = 0;
raw_cpu_inc(*tk->nhit);
@@ -1282,9 +1323,9 @@ static int kprobe_dispatcher(struct kprobe *kp, struct pt_regs *regs)
kprobe_trace_func(tk, regs);
#ifdef CONFIG_PERF_EVENTS
if (tk->tp.flags & TP_FLAG_PROFILE)
- kprobe_perf_func(tk, regs);
+ ret = kprobe_perf_func(tk, regs);
#endif
- return 0; /* We don't tweek kernel, so just return 0 */
+ return ret;
}
NOKPROBE_SYMBOL(kprobe_dispatcher);
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 903273c93e61..1140f8516242 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -253,6 +253,8 @@ struct symbol_cache;
unsigned long update_symbol_cache(struct symbol_cache *sc);
void free_symbol_cache(struct symbol_cache *sc);
struct symbol_cache *alloc_symbol_cache(const char *sym, long offset);
+int trace_kprobe_ftrace(struct trace_event_call *call);
+int trace_kprobe_error_injectable(struct trace_event_call *call);
#else
/* uprobes do not support symbol fetch methods */
#define fetch_symbol_u8 NULL
@@ -278,6 +280,16 @@ alloc_symbol_cache(const char *sym, long offset)
{
return NULL;
}
+
+static inline int trace_kprobe_ftrace(struct trace_event_call *call)
+{
+ return 0;
+}
+
+static inline int trace_kprobe_error_injectable(struct trace_event_call *call)
+{
+ return 0;
+}
#endif /* CONFIG_KPROBE_EVENTS */
struct probe_arg {
--
2.7.5
On 12/06/2017 05:12 PM, Josef Bacik wrote:
> Jon noticed that I had a typo in my _ASM_KPROBE_ERROR_INJECT macro. I went to
> figure out why the compiler didn't catch it and it's because it was not used
> anywhere. I had copied it from the trace blacklist code without understanding
> where it was used as cscope didn't find the original macro I was looking for, so
> I assumed it was some voodoo and left it in place. Turns out cscope failed me
> and I didn't need the macro at all, the trace blacklist thing I was looking at
> was for marking assembly functions as blacklisted and I have no intention of
> marking assembly functions as error injectable at the moment.
>
> v7->v8:
> - removed the _ASM_KPROBE_ERROR_INJECT since it was not needed.
The series doesn't apply cleanly to the bpf-next tree, so one last respin with
a rebase would unfortunately still be required, thanks!
On Fri, Dec 08, 2017 at 04:35:44PM +0100, Daniel Borkmann wrote:
> On 12/06/2017 05:12 PM, Josef Bacik wrote:
> > Jon noticed that I had a typo in my _ASM_KPROBE_ERROR_INJECT macro. I went to
> > figure out why the compiler didn't catch it and it's because it was not used
> > anywhere. I had copied it from the trace blacklist code without understanding
> > where it was used as cscope didn't find the original macro I was looking for, so
> > I assumed it was some voodoo and left it in place. Turns out cscope failed me
> > and I didn't need the macro at all, the trace blacklist thing I was looking at
> > was for marking assembly functions as blacklisted and I have no intention of
> > marking assembly functions as error injectable at the moment.
> >
> > v7->v8:
> > - removed the _ASM_KPROBE_ERROR_INJECT since it was not needed.
>
> The series doesn't apply cleanly to the bpf-next tree, so one last respin with
> a rebase would unfortunately still be required, thanks!
I've rebased and let it sit in my git tree to make sure kbuild test bot didn't
blow up, can you pull from
git://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-next.git bpf-override-return
or do you want me to repost the whole series? Thanks,
Josef
On 12/08/2017 09:24 PM, Josef Bacik wrote:
> On Fri, Dec 08, 2017 at 04:35:44PM +0100, Daniel Borkmann wrote:
>> On 12/06/2017 05:12 PM, Josef Bacik wrote:
>>> Jon noticed that I had a typo in my _ASM_KPROBE_ERROR_INJECT macro. I went to
>>> figure out why the compiler didn't catch it and it's because it was not used
>>> anywhere. I had copied it from the trace blacklist code without understanding
>>> where it was used as cscope didn't find the original macro I was looking for, so
>>> I assumed it was some voodoo and left it in place. Turns out cscope failed me
>>> and I didn't need the macro at all, the trace blacklist thing I was looking at
>>> was for marking assembly functions as blacklisted and I have no intention of
>>> marking assembly functions as error injectable at the moment.
>>>
>>> v7->v8:
>>> - removed the _ASM_KPROBE_ERROR_INJECT since it was not needed.
>>
>> The series doesn't apply cleanly to the bpf-next tree, so one last respin with
>> a rebase would unfortunately still be required, thanks!
>
> I've rebased and let it sit in my git tree to make sure kbuild test bot didn't
> blow up, can you pull from
>
> git://git.kernel.org/pub/scm/linux/kernel/git/josef/btrfs-next.git bpf-override-return
>
> or do you want me to repost the whole series? Thanks,
Yeah, the patches would need to end up on netdev, so once kbuild bot went
through fine after your rebase, please send the series.
Thanks,
Daniel