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Message-ID: <CALCETrX+FzK8njwWjREaw2+CNmpVeYi8ZLYDT1OPScNx9z31iQ@mail.gmail.com>
Date: Wed, 9 Dec 2015 15:13:31 -0800
From: Andy Lutomirski <luto@...capital.net>
To: Kees Cook <keescook@...omium.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, Michael Ellerman <mpe@...erman.id.au>,
Mathias Krause <minipli@...glemail.com>, Thomas Gleixner <tglx@...utronix.de>, X86 ML <x86@...nel.org>,
Arnd Bergmann <arnd@...db.de>, PaX Team <pageexec@...email.hu>, Emese Revfy <re.emese@...il.com>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v3 8/8] x86, vdso: mark vDSO read-only after init
On Wed, Dec 9, 2015 at 1:43 PM, Kees Cook <keescook@...omium.org> wrote:
> The vDSO does not need to be writable after __init, so mark it as
> __ro_after_init. The result kills the exploit method of writing to the
> vDSO from kernel space resulting in userspace executing the modified code,
> as shown here to bypass SMEP restrictions: http://itszn.com/blog/?p=21
>
> The memory map (with added vDSO address reporting) shows the vDSO moving
> into read-only memory:
>
> Before:
> [ 0.143067] vDSO @ ffffffff82004000
> [ 0.143551] vDSO @ ffffffff82006000
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffff81000000 16M pmd
> 0xffffffff81000000-0xffffffff81800000 8M ro PSE GLB x pmd
> 0xffffffff81800000-0xffffffff819f3000 1996K ro GLB x pte
> 0xffffffff819f3000-0xffffffff81a00000 52K ro NX pte
> 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd
> 0xffffffff81e00000-0xffffffff81e05000 20K ro GLB NX pte
> 0xffffffff81e05000-0xffffffff82000000 2028K ro NX pte
> 0xffffffff82000000-0xffffffff8214f000 1340K RW GLB NX pte
> 0xffffffff8214f000-0xffffffff82281000 1224K RW NX pte
> 0xffffffff82281000-0xffffffff82400000 1532K RW GLB NX pte
> 0xffffffff82400000-0xffffffff83200000 14M RW PSE GLB NX pmd
> 0xffffffff83200000-0xffffffffc0000000 974M pmd
>
> After:
> [ 0.145062] vDSO @ ffffffff81da1000
> [ 0.146057] vDSO @ ffffffff81da4000
> ---[ High Kernel Mapping ]---
> 0xffffffff80000000-0xffffffff81000000 16M pmd
> 0xffffffff81000000-0xffffffff81800000 8M ro PSE GLB x pmd
> 0xffffffff81800000-0xffffffff819f3000 1996K ro GLB x pte
> 0xffffffff819f3000-0xffffffff81a00000 52K ro NX pte
> 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd
> 0xffffffff81e00000-0xffffffff81e0b000 44K ro GLB NX pte
> 0xffffffff81e0b000-0xffffffff82000000 2004K ro NX pte
> 0xffffffff82000000-0xffffffff8214c000 1328K RW GLB NX pte
> 0xffffffff8214c000-0xffffffff8227e000 1224K RW NX pte
> 0xffffffff8227e000-0xffffffff82400000 1544K RW GLB NX pte
> 0xffffffff82400000-0xffffffff83200000 14M RW PSE GLB NX pmd
> 0xffffffff83200000-0xffffffffc0000000 974M pmd
>
> Based on work by PaX Team and Brad Spengler.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
Acked-by: Andy Lutomirski <luto@...nel.org>
--Andy
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