On Wed, May 18, 2011 at 10:50:30AM -0400, John Baldwin wrote: > On Wednesday, May 18, 2011 8:31:15 am Oliver Pinter wrote: > > On 5/18/11, Kostik Belousov <kostik...@gmail.com> wrote: > > > On Wed, May 18, 2011 at 02:03:07AM +0200, Oliver Pinter wrote: > > >> ---------- Forwarded message ---------- > > >> From: Fenghua Yu <fenghua...@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 <mi...@elte.hu>, Thomas Gleixner <t...@linutronix.de>, > > >> H Peter Anvin <h...@zytor.com>, Asit K Mallick > > >> <asit.k.mall...@intel.com>, Linus Torvalds > > >> <torva...@linux-foundation.org>, Avi Kivity <a...@redhat.com>, Arjan > > >> van de Ven <ar...@infradead.org>, Andrew Morton > > >> <a...@linux-foundation.org>, Andi Kleen <a...@firstfloor.org> > > >> Cc: linux-kernel <linux-ker...@vger.kernel.org>, Fenghua Yu > > >> <fenghua...@intel.com> > > >> > > >> From: Fenghua Yu <fenghua...@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...@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 > > Which revision? It is not documented in revision 38 from April 2011. > > I just downloaded that link, and it is still revision 38 and has no mention > 'SMEP'. Also, bit 20 of CR4 is still marked as Reserved in that manual > (section 2.5). This is exactly what I said about rev. 38 in my original reply.
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