[PATCH] kprobes/x86: Fix the return address of multiple kretprobes

KUMANO Syuhei
2010-08-15T06:18:09Z

Fix the return address of subsequent kretprobes when multiple
kretprobes are set on the same function.

For example:
# cd /sys/kernel/debug/tracing
# echo "r:event1 sys_symlink" > kprobe_events
# echo "r:event2 sys_symlink" >> kprobe_events
# echo 1 > events/kprobes/enable
# ln -s /tmp/foo /tmp/bar
(without this patch)
# cat trace
ln-897 [000] 20404.133727: event1: (kretprobe_trampoline+0x0/0x4c <- sys_symlink)
ln-897 [000] 20404.133747: event2: (system_call_fastpath+0x16/0x1b <- sys_symlink)
(with this patch)
# cat trace
ln-740 [000] 13799.491076: event1: (system_call_fastpath+0x16/0x1b <- sys_symlink)
ln-740 [000] 13799.491096: event2: (system_call_fastpath+0x16/0x1b <- sys_symlink)

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: x86@kernel.org
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: linux-kernel@vger.kernel.org
Cc: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Signed-off-by: KUMANO Syuhei <kumano.prog@gmail.com>
---
arch/x86/kernel/kprobes.c | 25 ++++++++++++++++++++++---
1 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c
index 675879b..5220e14 100644
--- a/arch/x86/kernel/kprobes.c
+++ b/arch/x86/kernel/kprobes.c
@@ -707,6 +707,7 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
struct hlist_node *node, *tmp;
unsigned long flags, orig_ret_address = 0;
unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
+ kprobe_opcode_t *correct_ret_addr = NULL;

INIT_HLIST_HEAD(&empty_rp);
kretprobe_hash_lock(current, &head, &flags);
@@ -738,14 +739,34 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
/* another task is sharing our hash bucket */
continue;

+ orig_ret_address = (unsigned long)ri->ret_addr;
+
+ if (orig_ret_address != trampoline_address)
+ /*
+ * This is the real return address. Any other
+ * instances associated with this task are for
+ * other calls deeper on the call stack
+ */
+ break;
+ }
+
+ kretprobe_assert(ri, orig_ret_address, trampoline_address);
+
+ correct_ret_addr = ri->ret_addr;
+ hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
+ if (ri->task != current)
+ /* another task is sharing our hash bucket */
+ continue;
+
+ orig_ret_address = (unsigned long)ri->ret_addr;
if (ri->rp && ri->rp->handler) {
__get_cpu_var(current_kprobe) = &ri->rp->kp;
get_kprobe_ctlblk()->kprobe_status = KPROBE_HIT_ACTIVE;
+ ri->ret_addr = correct_ret_addr;
ri->rp->handler(ri, regs);
__get_cpu_var(current_kprobe) = NULL;
}

- orig_ret_address = (unsigned long)ri->ret_addr;
recycle_rp_inst(ri, &empty_rp);

if (orig_ret_address != trampoline_address)
@@ -757,8 +778,6 @@ static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
break;
}

- kretprobe_assert(ri, orig_ret_address, trampoline_address);
-
kretprobe_hash_unlock(current, &flags);

hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
--
1.7.0.4