2023-05-13 09:30:56

by Ze Gao

Subject: [PATCH] kprobe: use preempt_{disable, enable}_notrace in kprobe_busy_{begin, end}

Replacing preempt_{disable, enable} with its corresponding notrace
version in kprobe_busy_{begin, end} because they are called by
fprobe_kprobe_handler. Such changes would resolve the potential
stack recursion or overflow problem introduced by preempt_count
_{add, sub} when these functions themselves accidentally traced
by fprobe+rethook, and does not break the original semantics.

Signed-off-by: Ze Gao <[email protected]>
---
kernel/kprobes.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 00e177de91cc..94d01b5d0646 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1242,7 +1242,7 @@ void kprobe_busy_begin(void)
{
struct kprobe_ctlblk *kcb;

- preempt_disable();
+ preempt_disable_notrace();
__this_cpu_write(current_kprobe, &kprobe_busy);
kcb = get_kprobe_ctlblk();
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
@@ -1251,7 +1251,7 @@ void kprobe_busy_begin(void)
void kprobe_busy_end(void)
{
__this_cpu_write(current_kprobe, NULL);
- preempt_enable();
+ preempt_enable_notrace();
}

/* Add the new probe to 'ap->list'. */
--
2.40.1

2023-05-31 10:22:00

by Masami Hiramatsu

Subject: Re: [PATCH] kprobe: use preempt_{disable, enable}_notrace in kprobe_busy_{begin, end}

Hi,

On Sat, 13 May 2023 17:05:48 +0800
Ze Gao <[email protected]> wrote:

> Replacing preempt_{disable, enable} with its corresponding notrace
> version in kprobe_busy_{begin, end} because they are called by
> fprobe_kprobe_handler. Such changes would resolve the potential
> stack recursion or overflow problem introduced by preempt_count
> _{add, sub} when these functions themselves accidentally traced
> by fprobe+rethook, and does not break the original semantics.

As I explained below;

https://lore.kernel.org/all/[email protected]/

we don't need this for kprobes because kprobes already prohibits
probing on preempt_count_{add,sub}, and we don't want to miss
tracing the preempt-off period by kprobes itself.

Thank you,

>
> Signed-off-by: Ze Gao <[email protected]>
> ---
> kernel/kprobes.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 00e177de91cc..94d01b5d0646 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -1242,7 +1242,7 @@ void kprobe_busy_begin(void)
> {
> struct kprobe_ctlblk *kcb;
>
> - preempt_disable();
> + preempt_disable_notrace();
> __this_cpu_write(current_kprobe, &kprobe_busy);
> kcb = get_kprobe_ctlblk();
> kcb->kprobe_status = KPROBE_HIT_ACTIVE;
> @@ -1251,7 +1251,7 @@ void kprobe_busy_begin(void)
> void kprobe_busy_end(void)
> {
> __this_cpu_write(current_kprobe, NULL);
> - preempt_enable();
> + preempt_enable_notrace();
> }
>
> /* Add the new probe to 'ap->list'. */
> --
> 2.40.1
>


--
Masami Hiramatsu (Google) <[email protected]>