On Wednesday, May 18, 2011 8:31:15 am Oliver Pinter wrote: > On 5/18/11, Kostik Belousov <[email protected]> wrote: > > On Wed, May 18, 2011 at 02:03:07AM +0200, Oliver Pinter wrote: > >> ---------- Forwarded message ---------- > >> From: Fenghua Yu <[email protected]> > >> Date: Mon, 16 May 2011 14:34:44 -0700 > >> Subject: [PATCH v2 3/4] x86, head_32/64.S: Enable SMEP > >> To: Ingo Molnar <[email protected]>, Thomas Gleixner <[email protected]>, > >> H Peter Anvin <[email protected]>, Asit K Mallick > >> <[email protected]>, Linus Torvalds > >> <[email protected]>, Avi Kivity <[email protected]>, Arjan > >> van de Ven <[email protected]>, Andrew Morton > >> <[email protected]>, Andi Kleen <[email protected]> > >> Cc: linux-kernel <[email protected]>, Fenghua Yu > >> <[email protected]> > >> > >> From: Fenghua Yu <[email protected]> > >> > >> 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 <[email protected]> > > > > 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). -- John Baldwin _______________________________________________ [email protected] mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to "[email protected]"
