Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754647AbbLIXNz (ORCPT ); Wed, 9 Dec 2015 18:13:55 -0500 Received: from mail-ob0-f178.google.com ([209.85.214.178]:36621 "EHLO mail-ob0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754436AbbLIXNw (ORCPT ); Wed, 9 Dec 2015 18:13:52 -0500 MIME-Version: 1.0 In-Reply-To: <1449697404-21076-9-git-send-email-keescook@chromium.org> References: <1449697404-21076-1-git-send-email-keescook@chromium.org> <1449697404-21076-9-git-send-email-keescook@chromium.org> From: Andy Lutomirski Date: Wed, 9 Dec 2015 15:13:31 -0800 Message-ID: Subject: Re: [PATCH v3 8/8] x86, vdso: mark vDSO read-only after init To: Kees Cook Cc: "linux-kernel@vger.kernel.org" , Ingo Molnar , "H. Peter Anvin" , Michael Ellerman , Mathias Krause , Thomas Gleixner , X86 ML , Arnd Bergmann , PaX Team , Emese Revfy , "kernel-hardening@lists.openwall.com" , linux-arch Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2965 Lines: 55 On Wed, Dec 9, 2015 at 1:43 PM, Kees Cook wrote: > The vDSO does not need to be writable after __init, so mark it as > __ro_after_init. The result kills the exploit method of writing to the > vDSO from kernel space resulting in userspace executing the modified code, > as shown here to bypass SMEP restrictions: http://itszn.com/blog/?p=21 > > The memory map (with added vDSO address reporting) shows the vDSO moving > into read-only memory: > > Before: > [ 0.143067] vDSO @ ffffffff82004000 > [ 0.143551] vDSO @ ffffffff82006000 > ---[ High Kernel Mapping ]--- > 0xffffffff80000000-0xffffffff81000000 16M pmd > 0xffffffff81000000-0xffffffff81800000 8M ro PSE GLB x pmd > 0xffffffff81800000-0xffffffff819f3000 1996K ro GLB x pte > 0xffffffff819f3000-0xffffffff81a00000 52K ro NX pte > 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd > 0xffffffff81e00000-0xffffffff81e05000 20K ro GLB NX pte > 0xffffffff81e05000-0xffffffff82000000 2028K ro NX pte > 0xffffffff82000000-0xffffffff8214f000 1340K RW GLB NX pte > 0xffffffff8214f000-0xffffffff82281000 1224K RW NX pte > 0xffffffff82281000-0xffffffff82400000 1532K RW GLB NX pte > 0xffffffff82400000-0xffffffff83200000 14M RW PSE GLB NX pmd > 0xffffffff83200000-0xffffffffc0000000 974M pmd > > After: > [ 0.145062] vDSO @ ffffffff81da1000 > [ 0.146057] vDSO @ ffffffff81da4000 > ---[ High Kernel Mapping ]--- > 0xffffffff80000000-0xffffffff81000000 16M pmd > 0xffffffff81000000-0xffffffff81800000 8M ro PSE GLB x pmd > 0xffffffff81800000-0xffffffff819f3000 1996K ro GLB x pte > 0xffffffff819f3000-0xffffffff81a00000 52K ro NX pte > 0xffffffff81a00000-0xffffffff81e00000 4M ro PSE GLB NX pmd > 0xffffffff81e00000-0xffffffff81e0b000 44K ro GLB NX pte > 0xffffffff81e0b000-0xffffffff82000000 2004K ro NX pte > 0xffffffff82000000-0xffffffff8214c000 1328K RW GLB NX pte > 0xffffffff8214c000-0xffffffff8227e000 1224K RW NX pte > 0xffffffff8227e000-0xffffffff82400000 1544K RW GLB NX pte > 0xffffffff82400000-0xffffffff83200000 14M RW PSE GLB NX pmd > 0xffffffff83200000-0xffffffffc0000000 974M pmd > > Based on work by PaX Team and Brad Spengler. > > Signed-off-by: Kees Cook Acked-by: Andy Lutomirski --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/