On Tue, 16 May 2023 13:25:02 +0900
Masami Hiramatsu (Google) [off-list ref] wrote:

Hi Ze Gao,

Thanks for the patch.

On Mon, 15 May 2023 11:26:38 +0800
Ze Gao [off-list ref] wrote:

quoted

This patch replace preempt_{disable, enable} with its corresponding
notrace version in rethook_trampoline_handler so no worries about stack
recursion or overflow introduced by preempt_count_{add, sub} under
fprobe + rethook context.

So, have you ever see that recursion of preempt_count overflow case?

I intended to use the normal preempt_disable() here because it does NOT
prohibit any function-trace call (Note that both kprobes and
fprobe checks recursive call by itself) but it is used for preempt_onoff
tracer.

OK, I got the point.

  rethook_trampoline_handler() {
    preempt_disable() {
      preempt_count_add() { => fprobe and set rethook
      } => rethook_trampoline_handler() {
        preempt_disable() {
          ...   

So the problem is that the preempt_disable() macro calls preempt_count_add()
which can be tracable.

So, let's make it notrace.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

and

Fixes: 54ecbe6f1ed5 ("rethook: Add a generic return hook")
Cc: stable@vger.kernel.org

Thank you,

Thanks,

quoted

Signed-off-by: Ze Gao <redacted>
---
 kernel/trace/rethook.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/rethook.c b/kernel/trace/rethook.c
index 32c3dfdb4d6a..60f6cb2b486b 100644
--- a/kernel/trace/rethook.c
+++ b/kernel/trace/rethook.c

@@ -288,7 +288,7 @@ unsigned long rethook_trampoline_handler(struct pt_regs *regs,
 	 * These loops must be protected from rethook_free_rcu() because those
 	 * are accessing 'rhn->rethook'.
 	 */
-	preempt_disable();
+	preempt_disable_notrace();
 
 	/*
 	 * Run the handler on the shadow stack. Do not unlink the list here because

@@ -321,7 +321,7 @@ unsigned long rethook_trampoline_handler(struct pt_regs *regs,
 		first = first->next;
 		rethook_recycle(rhn);
 	}
-	preempt_enable();
+	preempt_enable_notrace();
 
 	return correct_ret_addr;
 }

-- 
2.40.1

-- 
Masami Hiramatsu (Google) [off-list ref]

-- 
Masami Hiramatsu (Google) [off-list ref]