kernel-hardening - Re: [PATCH 14/14] arm64: add VMAP

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Message-ID: <20170815111910.GF6090@leverpostej>
Date: Tue, 15 Aug 2017 12:19:11 +0100
From: Mark Rutland <mark.rutland@....com>
To: Catalin Marinas <catalin.marinas@....com>
Cc: linux-arm-kernel@...ts.infradead.org, keescook@...omium.org,
	ard.biesheuvel@...aro.org, matt@...eblueprint.co.uk,
	kernel-hardening@...ts.openwall.com, will.deacon@....com,
	linux-kernel@...r.kernel.org, luto@...capital.net,
	james.morse@....com, labbott@...hat.com
Subject: Re: [PATCH 14/14] arm64: add VMAP_STACK overflow detection

On Tue, Aug 15, 2017 at 12:10:32PM +0100, Catalin Marinas wrote:
> On Mon, Aug 07, 2017 at 07:36:05PM +0100, Mark Rutland wrote:
> > diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> > index e5aa866..44a27c3 100644
> > --- a/arch/arm64/kernel/entry.S
> > +++ b/arch/arm64/kernel/entry.S
> > @@ -72,6 +72,37 @@
> >  	.macro kernel_ventry	label
> >  	.align 7
> >  	sub	sp, sp, #S_FRAME_SIZE
> > +#ifdef CONFIG_VMAP_STACK
> > +	add	sp, sp, x0			// sp' = sp + x0
> > +	sub	x0, sp, x0			// x0' = sp' - x0 = (sp + x0) - x0 = sp
> > +	tbnz	x0, #THREAD_SHIFT, 0f
> > +	sub	x0, sp, x0			// sp' - x0' = (sp + x0) - sp = x0
> > +	sub	sp, sp, x0			// sp' - x0 = (sp + x0) - x0 = sp
> > +	b	\label
> 
> Maybe a small comment before this hunk just to tell the user that it's
> trying to test a bit in SP without corrupting a gpr. It's obvious once
> you read it but not you see it for the first time ;).
> 
> > +
> > +	/* Stash the original SP value in tpidr_el0 */
> > +0:	msr	tpidr_el0, x0
> 
> And a comment here that on this path we no longer care about the user
> tpidr_el0 as we are never returning there.

Ok.

I've updated comments in both cases.

> Otherwise I'm fine with the series (I'm not a fan of the complexity it
> adds but I don't have a better suggestion).

Thanks!

I'll send out a v2 shortly with the changes you requested.

Thanks,
Mark.

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