Re: [PATCH] arm: kasan: clear stale stack poison

[Andrey Ryabinin]

On Tue, Apr 2, 2024 at 11:36 AM Mark Rutland <mark.rutland@xxxxxxx> wrote:
..
> It looks like you're specifically referring to what arm64 did in commit:
>
>   0d97e6d8024c71cc ("arm64: kasan: clear stale stack poison")
>
> Where the commit message explained the problem:
>
> | Functions which the compiler has instrumented for KASAN place poison on
> | the stack shadow upon entry and remove this poison prior to returning.
> |
> | In the case of cpuidle, CPUs exit the kernel a number of levels deep in
> | C code.  Any instrumented functions on this critical path will leave
> | portions of the stack shadow poisoned.
> |
> | If CPUs lose context and return to the kernel via a cold path, we
> | restore a prior context saved in __cpu_suspend_enter are forgotten, and
> | we never remove the poison they placed in the stack shadow area by
> | functions calls between this and the actual exit of the kernel.
> |
> | Thus, (depending on stackframe layout) subsequent calls to instrumented
> | functions may hit this stale poison, resulting in (spurious) KASAN
> | splats to the console.
> |
> | To avoid this, clear any stale poison from the idle thread for a CPU
> | prior to bringing a CPU online.
>
> ... which we then extended to check for CONFIG_KASAN_STACK in commit:
>
>   d56a9ef84bd0e1e8 ("kasan, arm64: unpoison stack only with CONFIG_KASAN_STACK")
>
> If you can fold in the description above (i.e. cite commit 0d97e6d8024c71cc and
> a copy of its commit message):
>
> Reviewed-by: Mark Rutland <mark.rutland@xxxxxxx>
>

Agreed with the above, feel free to add:

Acked-by: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>