linux-kernel - Re: [PATCH v4 8/8] x86, vdso: mark vDSO read-only after init

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Message-ID: <569EF642.90302@zytor.com>
Date:	Tue, 19 Jan 2016 18:51:46 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Michael Ellerman <mpe@...erman.id.au>,
	Mathias Krause <minipli@...glemail.com>,
	Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
	Arnd Bergmann <arnd@...db.de>, PaX Team <pageexec@...email.hu>,
	Emese Revfy <re.emese@...il.com>,
	kernel-hardening@...ts.openwall.com, linux-kernel@...r.kernel.org,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v4 8/8] x86, vdso: mark vDSO read-only after init

On 01/19/16 10:08, Kees Cook 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>

Acked-by: H. Peter Anvin <hpa@...ux.intel.com>