Re: [PATCH] x86: alternative: Fix int3 handling failure from broken text_poke array

[Peter Zijlstra]

On Wed, Jun 18, 2025 at 09:05:23AM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> 
> 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@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/CA+G9fYsLu0roY3DV=tKyqP7FEKbOEETRvTDhnpPxJGbA=Cg+4w@xxxxxxxxxxxxxx/
> Fixes: c8976ade0c1b ("x86/alternatives: Simplify smp_text_poke_single() by using tp_vec and existing APIs")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Reviewed-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> Tested-by: Linux Kernel Functional Testing <lkft@xxxxxxxxxx>

Thanks!