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

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Date:	Thu, 3 Mar 2016 14:14:29 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, lorenzo.pieralisi@....com
Cc:	akpm@...ux-foundation.org, aryabinin@...tuozzo.com,
	catalin.marinas@....com, glider@...gle.com, mingo@...hat.com,
	peterz@...radead.org, will.deacon@....com
Subject: Re: [PATCH 3/3] arm64: kasan: clear stale stack poison

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@....com>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Andrey Ryabinin <aryabinin@...tuozzo.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
> Cc: Will Deacon <will.deacon@....com>
> ---
>  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