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Subject[PATCH] kprobe: sync issue's on ftraced-kprobe.
Date
In kprobe_ftrace_handler, it accesses get kporbe without kprobe_mutex
held.

This makes some of synchronizing issue when we use kprobe API in
kernel-module.

Below is what i experienced:

CPU 0 CPU 1
<...> <In module code>
kprobe_ftrace_handler
get_kprobe
__this_cpu_write
unregister_kprobe
unload_module
< kprobe memory gone>
p->pre_handler <access invalid memory>
page_fault
kprobe_fault_handler
(In here, kprobe memory gone,
double page fault is happening inifinie).

Signed-off-by: Levi Yun <ppbuk5246@gmail.com>
---
arch/x86/kernel/kprobes/ftrace.c | 3 +++
include/linux/kprobes.h | 2 ++
kernel/kprobes.c | 2 +-
3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/kprobes/ftrace.c b/arch/x86/kernel/kprobes/ftrace.c
index dd2ec14adb77..76147ff6ed88 100644
--- a/arch/x86/kernel/kprobes/ftrace.c
+++ b/arch/x86/kernel/kprobes/ftrace.c
@@ -25,6 +25,7 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
if (bit < 0)
return;

+ mutex_lock(&kprobe_mutex);
p = get_kprobe((kprobe_opcode_t *)ip);
if (unlikely(!p) || kprobe_disabled(p))
goto out;
@@ -57,7 +58,9 @@ void kprobe_ftrace_handler(unsigned long ip, unsigned long parent_ip,
*/
__this_cpu_write(current_kprobe, NULL);
}
+
out:
+ mutex_unlock(&kprobe_mutex);
ftrace_test_recursion_unlock(bit);
}
NOKPROBE_SYMBOL(kprobe_ftrace_handler);
diff --git a/include/linux/kprobes.h b/include/linux/kprobes.h
index 157168769fc2..4a18147ff6d6 100644
--- a/include/linux/kprobes.h
+++ b/include/linux/kprobes.h
@@ -191,6 +191,8 @@ struct kprobe_blacklist_entry {
DECLARE_PER_CPU(struct kprobe *, current_kprobe);
DECLARE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

+extern struct mutex kprobe_mutex;
+
extern void kprobe_busy_begin(void);
extern void kprobe_busy_end(void);

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index dd58c0be9ce2..b65f055b6fa2 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -64,7 +64,7 @@ static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];
static bool kprobes_all_disarmed;

/* This protects 'kprobe_table' and 'optimizing_list' */
-static DEFINE_MUTEX(kprobe_mutex);
+DEFINE_MUTEX(kprobe_mutex);
static DEFINE_PER_CPU(struct kprobe *, kprobe_instance);

kprobe_opcode_t * __weak kprobe_lookup_name(const char *name,
--
2.35.1
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