Re: [PATCH 3/3] arm64: kasan: clear stale stack poison

[Mark Rutland]

On Wed, Mar 02, 2016 at 02:26:18PM +0000, Mark Rutland wrote:
> Functions which the compiler has instrumented for ASAN 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.
> 
> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> Cc: Will Deacon <will.deacon@xxxxxxx>
> ---
>  arch/arm64/kernel/sleep.S | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/arm64/kernel/sleep.S b/arch/arm64/kernel/sleep.S
> index e33fe33..fd10eb6 100644
> --- a/arch/arm64/kernel/sleep.S
> +++ b/arch/arm64/kernel/sleep.S
> @@ -145,6 +145,10 @@ ENTRY(cpu_resume_mmu)
>  ENDPROC(cpu_resume_mmu)
>  	.popsection
>  cpu_resume_after_mmu:
> +#ifdef CONFIG_KASAN
> +	mov	x0, sp
> +	bl	kasan_unpoison_remaining_stack
> +#endif

Lorenzo, as this was following your suggestion [1], I hope that this
patch looks ok to you?

Are you happy to provide an Ack / Reviewed-by?

Thanks,
Mark.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-March/413061.html