linux-kernel - Re: [PATCH] x86: alternative: Fix int3 handling failure from broken text

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Message-ID: <20250618115737.GI1613376@noisy.programming.kicks-ass.net>
Date: Wed, 18 Jun 2025 13:57:37 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Ingo Molnar <mingo@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Steven Rostedt <rostedt@...dmis.org>, x86@...nel.org,
	Naresh Kamboju <naresh.kamboju@...aro.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: [PATCH] x86: alternative: Fix int3 handling failure from broken
 text_poke array

On Wed, Jun 18, 2025 at 09:05:23AM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> 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 because of bsearch failing;
> 
> 
>    CPU 0                        CPU 1                      CPU 2
>    -----                        -----                      -----
> 
>  smp_text_poke_batch_add()
> 
> 			    smp_text_poke_single() <<-- Adds out of order
> 
> 							<int3>
>                                                 	[Fails o find address
>                                                         in text_poke_array ]
>                                                         OOPS!
> 
> Or unhandled page fault because of a buffer overflow;
> 
> 
>    CPU 0                        CPU 1
>    -----                        -----
> 
>  smp_text_poke_batch_add() <<+
>  ...                         |
>  smp_text_poke_batch_add() <<-- Adds TEXT_POKE_ARRAY_MAX times.
> 
> 			     smp_text_poke_single() {
> 			     	__smp_text_poke_batch_add() <<-- Adds entry at
> 								TEXT_POKE_ARRAY_MAX + 1
> 
>                 		smp_text_poke_batch_finish()
>                         	  [Unhandled page fault because
> 				   text_poke_array.nr_entries is
> 				   overwritten]
> 				   BUG!
> 			     }
> 
> 
> 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: c8976ade0c1b ("x86/alternatives: Simplify smp_text_poke_single() by using tp_vec and existing APIs")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> Reviewed-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> Tested-by: Linux Kernel Functional Testing <lkft@...aro.org>

Thanks!