From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756844Ab2IUWHS (ORCPT ); Fri, 21 Sep 2012 18:07:18 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:57747 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752416Ab2IUWHQ convert rfc822-to-8bit (ORCPT ); Fri, 21 Sep 2012 18:07:16 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: "H. Peter Anvin" Cc: Linux Kernel Mailing List , "H. Peter Anvin" , Ingo Molnar , Thomas Gleixner , Linus Torvalds , Kees Cook , Linda Wang , Matt Fleming References: <1348256595-29119-1-git-send-email-hpa@linux.intel.com> Date: Fri, 21 Sep 2012 15:07:07 -0700 In-Reply-To: <1348256595-29119-1-git-send-email-hpa@linux.intel.com> (H. Peter Anvin's message of "Fri, 21 Sep 2012 12:43:04 -0700") Message-ID: <877grnows4.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=;;;mid=;;;hst=in01.mta.xmission.com;;;ip=98.207.153.68;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX196t1kh0hb0IEHu/TeBz0x+gkDtcJlEndo= X-SA-Exim-Connect-IP: 98.207.153.68 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: T_TM2_M_HEADER_IN_MSG * -3.0 BAYES_00 BODY: Bayes spam probability is 0 to 1% * [score: 0.0000] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa06 1397; Body=1 Fuz1=1 Fuz2=1] * 0.5 XM_Body_Dirty_Words Contains a dirty word X-Spam-DCC: XMission; sa06 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: ;"H. Peter Anvin" X-Spam-Relay-Country: Subject: Re: [PATCH 00/11] x86: Supervisor Mode Access Prevention X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Fri, 06 Aug 2010 16:31:04 -0600) X-SA-Exim-Scanned: Yes (on in01.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "H. Peter Anvin" writes: > Supervisor Mode Access Prevention (SMAP) is a new security feature > disclosed by Intel in revision 014 of the Intel® Architecture > Instruction Set Extensions Programming Reference: > > http://software.intel.com/sites/default/files/319433-014.pdf > > When SMAP is active, the kernel cannot normally access pages that are > user space (U=1). Since the kernel does have the need to access user > space pages under specific circumstances, an override is provided: the > kernel can access user space pages if EFLAGS.AC=1. For system data > structures, e.g. descriptor tables, that are accessed by the processor > directly, SMAP is active even in CPL 3 regardless of EFLAGS.AC. > > SMAP also includes two new instructions, STAC and CLAC, to flip the AC > flag more quickly. Have you tested kexec in this environment? This is the kind of cpu feature that when we enable it, frequently we have to do something on the kexec path. At a quick skim it looks like the kexec path is using kernel page table entries and clearing all bits from cr4 except X86_CR4_PAE so I don't actually expect this change will require anything on the kexec path. Eric