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

From "H. Peter Anvin" <hpa@zytor.com>
Newsgroups linux.kernel
Subject Re: [PATCH v4 8/8] x86, vdso: mark vDSO read-only after init
Date 2016-01-20 04:00 +0100
Message-ID <qSRa2-5e-9@gated-at.bofh.it> (permalink)
References <qSIT8-33H-5@gated-at.bofh.it> <qSIT9-33H-29@gated-at.bofh.it>
Organization linux.* mail to news gateway

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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@chromium.org>
> Acked-by: Andy Lutomirski <luto@kernel.org>

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

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Thread

[PATCH v4 8/8] x86, vdso: mark vDSO read-only after init Kees Cook <keescook@chromium.org> - 2016-01-19 19:10 +0100
  Re: [PATCH v4 8/8] x86, vdso: mark vDSO read-only after init Andy Lutomirski <luto@amacapital.net> - 2016-01-19 20:10 +0100
  Re: [PATCH v4 8/8] x86, vdso: mark vDSO read-only after init "H. Peter Anvin" <hpa@zytor.com> - 2016-01-20 04:00 +0100
  Re: [PATCH v4 8/8] x86, vdso: mark vDSO read-only after init Andy Lutomirski <luto@amacapital.net> - 2016-01-20 04:00 +0100

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