Date: Wed, 18 May 2011 18:40:07 +0300 From: Kostik Belousov <kostikbel@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: freebsd-hackers@freebsd.org, Oliver Pinter <oliver.pntr@gmail.com> Subject: Re: Fwd: [PATCH v2 3/4] x86, head_32/64.S: Enable SMEP Message-ID: <20110518154007.GR48734@deviant.kiev.zoral.com.ua> In-Reply-To: <201105181050.30128.jhb@freebsd.org> References: <1305581685-5144-1-git-send-email-fenghua.yu@intel.com> <20110518010353.GQ48734@deviant.kiev.zoral.com.ua> <BANLkTimHmZCO9couAxsW1rf81Qm2FAHrZw@mail.gmail.com> <201105181050.30128.jhb@freebsd.org>
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--mqabeeRFEDQfpoIl Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable 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 <kostikbel@gmail.com> wrote: > > > On Wed, May 18, 2011 at 02:03:07AM +0200, Oliver Pinter wrote: > > >> ---------- Forwarded message ---------- > > >> From: Fenghua Yu <fenghua.yu@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@elte.hu>, Thomas Gleixner <tglx@linutronix.de= >, > > >> H Peter Anvin <hpa@zytor.com>, Asit K Mallick > > >> <asit.k.mallick@intel.com>, Linus Torvalds > > >> <torvalds@linux-foundation.org>, Avi Kivity <avi@redhat.com>, Arjan > > >> van de Ven <arjan@infradead.org>, Andrew Morton > > >> <akpm@linux-foundation.org>, Andi Kleen <andi@firstfloor.org> > > >> Cc: linux-kernel <linux-kernel@vger.kernel.org>, Fenghua Yu > > >> <fenghua.yu@intel.com> > > >> > > >> From: Fenghua Yu <fenghua.yu@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 t= hat > > >> does > > >> not have the kernel/system flag set in the pte. This prevents the ke= rnel > > >> 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 co= de > > >> identical to XD violation. > > >> > > >> CR4.SMEP (bit 20) is 0 at power-on. If the feature is supported by C= PU > > >> (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@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. > >=20 > > http://www.intel.com/Assets/PDF/manual/325384.pdf > >=20 > > Intel? 64 and IA-32 Architectures Software Developer?s Manual > > Volume 3 (3A & 3B): > > System Programming Guide >=20 > Which revision? It is not documented in revision 38 from April 2011. >=20 > I just downloaded that link, and it is still revision 38 and has no menti= on=20 > 'SMEP'. Also, bit 20 of CR4 is still marked as Reserved in that manual= =20 > (section 2.5). This is exactly what I said about rev. 38 in my original reply. --mqabeeRFEDQfpoIl Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.11 (FreeBSD) iEYEARECAAYFAk3T6FcACgkQC3+MBN1Mb4i6bACgxDsmB8Xdzjrx728CaaFis+sd 5v0AoKnzcbE0AAWzbNh6ayeULLg6/0tv =1K4X -----END PGP SIGNATURE----- --mqabeeRFEDQfpoIl--
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