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Date: Sat, 13 Feb 2016 10:00:56 +0100
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: David Brown <david.brown@...aro.org>
Cc: kernel-hardening@...ts.openwall.com,
Catalin Marinas <catalin.marinas@....com>, Will Deacon <will.deacon@....com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH] arm64: vdso: Mark vDSO code as read-only
On 13 February 2016 at 01:31, David Brown <david.brown@...aro.org> wrote:
> On Thu, Feb 11, 2016 at 03:19:20PM +0100, Ard Biesheuvel wrote:
>
>>> diff --git a/arch/arm64/kernel/vdso/vdso.S
>>> b/arch/arm64/kernel/vdso/vdso.S
>>> index 60c1db5..db7c0f2 100644
>>> --- a/arch/arm64/kernel/vdso/vdso.S
>>> +++ b/arch/arm64/kernel/vdso/vdso.S
>>> @@ -24,6 +24,7 @@
>>> __PAGE_ALIGNED_DATA
>>
>>
>> ^^ You can get rid of this now as well
>
>
> Can we? The page is getting mapped to userspace, and if we didn't
> page align it, we could leak kernel read-only data to every userspace
> process.
>
That's what the .balign is for. __PAGE_ALIGNED_DATA only sets the
section, and you're overriding that right after.
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