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

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Message-ID: <20160218181356.GF2538@e104818-lin.cambridge.arm.com>
Date:	Thu, 18 Feb 2016 18:13:57 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Will Deacon <will.deacon@....com>
Cc:	Mark Rutland <mark.rutland@....com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de,
	Andrey Ryabinin <aryabinin@...tuozzo.com>,
	akpm@...ux-foundation.org, hpa@...ux.intel.com, mingo@...nel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: kasan: clear stale stack poison

On Thu, Feb 18, 2016 at 06:03:54PM +0000, Will Deacon wrote:
> On Thu, Feb 18, 2016 at 05:54:47PM +0000, Catalin Marinas wrote:
> > On Thu, Feb 18, 2016 at 05:27:38PM +0000, Mark Rutland wrote:
> > > @@ -145,6 +146,7 @@ ENTRY(cpu_resume_mmu)
> > >  ENDPROC(cpu_resume_mmu)
> > >  	.popsection
> > >  cpu_resume_after_mmu:
> > > +	kasan_unpoison_stack 96
> > 
> > I don't think the 96 here is needed since we populate the stack in
> > assembly (__cpu_suspend_enter) and unwind it again still in assembly
> > (cpu_resume_after_mmu), so no KASAN shadow writes/reads.
> > 
> > Otherwise the patch looks fine.
> 
> I'd much rather it was written in C -- is there a reason we can't do
> that if we use a separate compilation unit where the compiler will
> honour the fno-sanitize flag?

A simple, non-sanitised C wrapper around __cpu_suspend_enter() would
probably work. We need to make sure it is static inline when !KASAN to
avoid an unnecessary function call. Or we just move cpu_suspend() to a
different compilation unit, though that's a slightly larger function
which we may want to track under KASAN.

-- 
Catalin