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Message-ID: <20170815111031.xbga45isn5gumeni@armageddon.cambridge.arm.com>
Date: Tue, 15 Aug 2017 12:10:32 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Mark Rutland <mark.rutland@....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 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.
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).
--
Catalin
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