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Message-ID: <4FBE77D4.4080109@mvista.com>
Date: Thu, 24 May 2012 11:03:00 -0700
From: akuster <akuster@...sta.com>
To: oss-security@...ts.openwall.com
Subject: Re: CVE Request -- kernel: mm: read_pmd_atomic: 32bit
PAE pmd walk vs pmd_populate SMP race condition
is 1a5a9906d4e8d1976b701f889d8f35d54b928f25 the upstream fix?
-armin
On 05/18/2012 02:37 AM, Petr Matousek wrote:
> When holding the mmap_sem for reading, pmd_offset_map_lock should only
> run on a pmd_t that has been read atomically from the pmdp
> pointer, otherwise we may read only half of it leading to this crash.
>
> PID: 11679 TASK: f06e8000 CPU: 3 COMMAND: "do_race_2_panic"
> #0 [f06a9dd8] crash_kexec at c049b5ec
> #1 [f06a9e2c] oops_end at c083d1c2
> #2 [f06a9e40] no_context at c0433ded
> #3 [f06a9e64] bad_area_nosemaphore at c043401a
> #4 [f06a9e6c] __do_page_fault at c0434493
> #5 [f06a9eec] do_page_fault at c083eb45
> #6 [f06a9f04] error_code (via page_fault) at c083c5d5
> EAX: 01fb470c EBX: fff35000 ECX: 00000003 EDX: 00000100 EBP:
> 00000000
> DS: 007b ESI: 9e201000 ES: 007b EDI: 01fb4700 GS: 00e0
> CS: 0060 EIP: c083bc14 ERR: ffffffff EFLAGS: 00010246
> #7 [f06a9f38] _spin_lock at c083bc14
> #8 [f06a9f44] sys_mincore at c0507b7d
> #9 [f06a9fb0] system_call at c083becd
> start len
> EAX: ffffffda EBX: 9e200000 ECX: 00001000 EDX: 6228537f
> DS: 007b ESI: 00000000 ES: 007b EDI: 003d0f00
> SS: 007b ESP: 62285354 EBP: 62285388 GS: 0033
> CS: 0073 EIP: 00291416 ERR: 000000da EFLAGS: 00000286
>
> This should be a longstanding bug affecting x86 32bit PAE without
> THP. Only archs with 64bit large pmd_t and 32bit unsigned long should
> be affected.
>
> An unprivileged local user could use this flaw to crash the system.
>
> Proposed fix:
> http://permalink.gmane.org/gmane.linux.kernel.mm/78590
>
> References:
> https://bugzilla.redhat.com/show_bug.cgi?id=822821
> http://permalink.gmane.org/gmane.linux.kernel.mm/78590
>
> Thanks,
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