linux-kernel - Re: [PATCH v3 07/21] arm64: move kernel image to base of vmalloc area

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Message-ID: <20160115112306.GC3262@leverpostej>
Date:	Fri, 15 Jan 2016 11:23:07 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:	Kees Cook <keescook@...omium.org>, Arnd Bergmann <arnd@...db.de>,
	kernel-hardening@...ts.openwall.com,
	Sharma Bhupesh <bhupesh.sharma@...escale.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	Stuart Yoder <stuart.yoder@...escale.com>,
	Marc Zyngier <marc.zyngier@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 07/21] arm64: move kernel image to base of vmalloc area

On Fri, Jan 15, 2016 at 10:54:26AM +0100, Ard Biesheuvel wrote:
> On 14 January 2016 at 19:57, Mark Rutland <mark.rutland@....com> wrote:
> > On Wed, Jan 13, 2016 at 01:51:10PM +0000, Mark Rutland wrote:
> >> On Wed, Jan 13, 2016 at 09:39:41AM +0100, Ard Biesheuvel wrote:
> >> > If I remove the rounding, I get false positive kasan errors which I
> >> > have not quite diagnosed yet, but are probably due to the fact that
> >> > the rounding performed by vmemmap_populate() goes in the wrong
> >> > direction.
> >
> > As far as I can see, it implicitly rounds the base down and end up to
> > SWAPPER_BLOCK_SIZE granularity.
> >
> > I can see that it might map too much memory, but I can't see why that
> > should trigger KASAN failures. Regardless of what was mapped KASAN
> > should stick to the region it cares about, and everything else should
> > stay out of that.
> >
> > When do you see the failures, and are they in any way consistent?
> >
> > Do you have an example to hand?
> >
> 
> For some reason, this issue has evaporated, i.e., I can no longer
> reproduce it on my WIP v4 branch.
> So I will remove the rounding.

Ok.

I'll let you know if I stumble across anything that looks like a
potential cause of the KASAN failures, and I'll try to give v4 a go at
some point soon.

Thanks,
Mark.