linux-kernel - Re: next-20250605: Test regression: qemu-x86_64-compat mode ltp tracing Oops int3 kernel panic

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Message-ID: <CA+G9fYtuiFHYBuRpB5MVwnZqc+WVRnnYMRHUExXAyu3_jMVurQ@mail.gmail.com>
Date: Tue, 17 Jun 2025 17:40:25 +0530
From: Naresh Kamboju <naresh.kamboju@...aro.org>
To: Masami Hiramatsu <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, open list <linux-kernel@...r.kernel.org>, 
	Linux trace kernel <linux-trace-kernel@...r.kernel.org>, lkft-triage@...ts.linaro.org, 
	Stephen Rothwell <sfr@...b.auug.org.au>, Arnd Bergmann <arnd@...db.de>, 
	Dan Carpenter <dan.carpenter@...aro.org>, Anders Roxell <anders.roxell@...aro.org>
Subject: Re: next-20250605: Test regression: qemu-x86_64-compat mode ltp
 tracing Oops int3 kernel panic

Hi Masami,

On Tue, 17 Jun 2025 at 16:12, Masami Hiramatsu <mhiramat@...nel.org> wrote:
>
> On Mon, 16 Jun 2025 16:36:59 +0900
> Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
>
> > > So the fundamental issue is that smp_text_poke_batch missed
> > > handling INT3.
> > >
> > > I guess some text_poke user do not get text_mutex?
> >
> > Hmm, I've checked the smp_text_poke_* users, but it seems no problem.
> > Basically, those smp_text_poke* user locks text_mutex, and another
> > suspicious ftrace_start_up is also set under ftrace_lock.
> > ftrace_arch_code_modify_post_process() is also paired with
> > ftrace_arch_code_modify_prepare() and under ftrace_lock.
>
> Eventually, I found a bug in text_poke, and jump_label
> (tracepoint) hit the bug.
>
> The jump_label uses 2 different APIs (single and batch)
> which independently takes text_mutex lock.
>
> smp_text_poke_single()
>   __jump_label_transform()
>     jump_label_transform() --> lock text_mutex
>
> smp_text_poke_batch_add()
>   arch_jump_label_transform_queue() -> lock text_mutex
>
> smp_text_poke_batch_finish()
>   arch_jump_label_transform_apply() -> lock text_mutex
>
> This is allowed by commit 8a6a1b4e0ef1 ("x86/alternatives:
> Remove the mixed-patching restriction on smp_text_poke_single()"),
> but smp_text_poke_single() still expects that the batched
> APIs are run in the same text_mutex lock region.
> Thus if user calls those APIs in the below order;
>
> arch_jump_label_transform_queue(addr1)
> jump_label_transform(addr2)
> arch_jump_label_transform_apply()
>
> And if the addr1 > addr2, the bsearch on the array
> does not work, and failed to handle int3!
>
> This can explain the disappeared int3 case. If it happens
> right before int3 is overwritten, that int3 will be
> overwritten when the int3 handler dumps the code, but
> text_poke_array_refs is still 1.
>
> It seems that commit c8976ade0c1b ("x86/alternatives:
> Simplify smp_text_poke_single() by using tp_vec and existing APIs")
> introduced this problem, because it shares the global array in
> the text_poke_batch and text_poke_single. Before that commit,
> text_poke_single (text_poke_bp) uses its local variable.
>
> To fix this issue, Use smp_text_poke_batch_add() in
> smp_text_poke_single(), which checks whether the array
> sorted and the array index does not overflow.
>
> Please test below;
>

Do you mean only this single patch on top of the Linux next ?

>
> From e2a49c7cefb4148ea3142c752396d39f103c9f4d Mon Sep 17 00:00:00 2001
> From: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
> Date: Tue, 17 Jun 2025 19:18:37 +0900
> Subject: [PATCH] x86: alternative: Fix int3 handling failure from broken
>  text_poke array
>
> Since smp_text_poke_single() does not expect there is another
> text_poke request is queued, it can make text_poke_array not
> sorted or cause a buffer overflow on the text_poke_array.vec[].
> This will cause an Oops in int3, or kernel page fault if it causes
> a buffer overflow.
>
> Use smp_text_poke_batch_add() instead of __smp_text_poke_batch_add()
> so that it correctly flush the queue if needed.
>
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> Closes: https://lore.kernel.org/all/CA+G9fYsLu0roY3DV=tKyqP7FEKbOEETRvTDhnpPxJGbA=Cg+4w@mail.gmail.com/
> Fixes: 8976ade0c1b ("x86/alternatives: Simplify smp_text_poke_single() by using tp_vec and existing APIs")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
>  arch/x86/kernel/alternative.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
> index ecfe7b497cad..8038951650c6 100644
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -3107,6 +3107,6 @@ void __ref smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, c
>   */
>  void __ref smp_text_poke_single(void *addr, const void *opcode, size_t len, const void *emulate)
>  {
> -       __smp_text_poke_batch_add(addr, opcode, len, emulate);
> +       smp_text_poke_batch_add(addr, opcode, len, emulate);
>         smp_text_poke_batch_finish();
>  }
> --
> 2.50.0.rc2.692.g299adb8693-goog
>
>
>
>
> --
> Masami Hiramatsu (Google) <mhiramat@...nel.org>