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

Masami Hiramatsu
2010-08-17T15:10:15Z

KUMANO Syuhei wrote:
> 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)
>

Yeah, I'm OK for this fix.

Acked-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Ingo, could you pull this on your x86/bugfix tree?

Thank you,

> 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) {