Fwd: [PATCH v2 3/4] x86, head_32/64.S: Enable SMEP

[Oliver Pinter]

On 5/18/11, Kostik Belousov <kostikbel at gmail.com> wrote:
> On Wed, May 18, 2011 at 02:03:07AM +0200, Oliver Pinter wrote:
>> ---------- Forwarded message ----------
>> From: Fenghua Yu <fenghua.yu at intel.com>
>> Date: Mon, 16 May 2011 14:34:44 -0700
>> Subject: [PATCH v2 3/4] x86, head_32/64.S: Enable SMEP
>> To: Ingo Molnar <mingo at elte.hu>, Thomas Gleixner <tglx at linutronix.de>,
>> H Peter Anvin <hpa at zytor.com>, Asit K Mallick
>> <asit.k.mallick at intel.com>, Linus Torvalds
>> <torvalds at linux-foundation.org>, Avi Kivity <avi at redhat.com>, Arjan
>> van de Ven <arjan at infradead.org>, Andrew Morton
>> <akpm at linux-foundation.org>, Andi Kleen <andi at firstfloor.org>
>> Cc: linux-kernel <linux-kernel at vger.kernel.org>, Fenghua Yu
>> <fenghua.yu at intel.com>
>>
>> From: Fenghua Yu <fenghua.yu at intel.com>
>>
>> Enable newly documented SMEP (Supervisor Mode Execution Protection) CPU
>> feature in kernel.
>>
>> SMEP prevents the CPU in kernel-mode to jump to an executable page that
>> does
>> not have the kernel/system flag set in the pte. This prevents the kernel
>> from executing user-space code accidentally or maliciously, so it for
>> example
>> prevents kernel exploits from jumping to specially prepared user-mode
>> shell
>> code. The violation will cause page fault #PF and will have error code
>> identical to XD violation.
>>
>> CR4.SMEP (bit 20) is 0 at power-on. If the feature is supported by CPU
>> (X86_FEATURE_SMEP), enable SMEP by setting CR4.SMEP. New kernel
>> option nosmep disables the feature even if the feature is supported by
>> CPU.
>>
>> Signed-off-by: Fenghua Yu <fenghua.yu at intel.com>
>
> So, where is the mentioned documentation for SMEP ? Rev. 38 of the
> Intel(R) 64 and IA-32 Architectures Software Developer's Manual does
> not contain the description, at least at the places where I looked and
> expected to find it.

http://www.intel.com/Assets/PDF/manual/325384.pdf

Intel® 64 and IA-32 Architectures Software Developer’s Manual
                   Volume 3 (3A & 3B):
             System Programming Guide



>
> Looking forward to hear from you.
>
>