From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dan Williams Subject: Re: [PATCH v4 00/10] prevent bounds-check bypass via speculative execution Date: Fri, 19 Jan 2018 22:58:44 -0800 Message-ID: References: <151632009605.21271.11304291057104672116.stgit@dwillia2-desk3.amr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <151632009605.21271.11304291057104672116.stgit@dwillia2-desk3.amr.corp.intel.com> Sender: stable-owner@vger.kernel.org To: Linux Kernel Mailing List Cc: Mark Rutland , Kernel Hardening , Peter Zijlstra , Catalin Marinas , Will Deacon , "H. Peter Anvin" , Elena Reshetova , linux-arch , Andi Kleen , Jonathan Corbet , X86 ML , Russell King , Ingo Molnar , Andrew Honig , Alan Cox , Tom Lendacky , Kees Cook , Al Viro , Andy Lutomirski , Thomas Gleixner An List-Id: linux-arch.vger.kernel.org On Thu, Jan 18, 2018 at 4:01 PM, Dan Williams wrote: > Changes since v3 [1] > * Drop 'ifence_array_ptr' and associated compile-time + run-time > switching and just use the masking approach all the time. > > * Convert 'get_user' to use pointer sanitization via masking rather than > lfence. '__get_user' and associated paths still rely on > lfence. (Linus) > > "Basically, the rule is trivial: find all 'stac' users, and use > address masking if those users already integrate the limit > check, and lfence they don't." > > * At syscall entry sanitize the syscall number under speculation > to remove a user controlled pointer de-reference in kernel > space. (Linus) > > * Fix a raw lfence in the kvm code (added for v4.15-rc8) to use > 'array_ptr'. > > * Propose 'array_idx' as a way to sanitize user input that is > later used as an array index, but where the validation is > happening in a different code block than the array reference. > (Christian). > > * Fix grammar in speculation.txt (Kees) > > --- > > Quoting Mark's original RFC: > > "Recently, Google Project Zero discovered several classes of attack > against speculative execution. One of these, known as variant-1, allows > explicit bounds checks to be bypassed under speculation, providing an > arbitrary read gadget. Further details can be found on the GPZ blog [2] > and the Documentation patch in this series." > > A precondition of using this attack on the kernel is to get a user > controlled pointer de-referenced (under speculation) in privileged code. > The primary source of user controlled pointers in the kernel is the > arguments passed to 'get_user' and '__get_user'. An example of other > user controlled pointers are user-controlled array / pointer offsets. > > Better tooling is needed to find more arrays / pointers with user > controlled indices / offsets that can be converted to use 'array_ptr' or > 'array_idx'. A few are included in this set, and these are not expected > to be complete. That said, the 'get_user' protections raise the bar on > finding a vulnerable gadget in the kernel. > > These patches are also available via the 'nospec-v4' git branch here: > > git://git.kernel.org/pub/scm/linux/kernel/git/djbw/linux nospec-v4 I've pushed out a nospec-v4.1 with the below minor cleanup, a fixup of the changelog for "kvm, x86: fix spectre-v1 mitigation", and added Paolo's ack. git://git.kernel.org/pub/scm/linux/kernel/git/djbw/linux nospec-v4.1 diff --git a/include/linux/nospec.h b/include/linux/nospec.h index 8af35be1869e..b8a9222e34d1 100644 --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -37,7 +37,7 @@ static inline unsigned long array_ptr_mask(unsigned long idx, unsigned long sz) unsigned long _i = (idx); \ unsigned long _mask = array_ptr_mask(_i, (sz)); \ \ - __u._ptr = _arr + (_i & _mask); \ + __u._ptr = _arr + _i; \ __u._bit &= _mask; \ __u._ptr; \ }) From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f65.google.com ([209.85.218.65]:44803 "EHLO mail-oi0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751153AbeATG6p (ORCPT ); Sat, 20 Jan 2018 01:58:45 -0500 Received: by mail-oi0-f65.google.com with SMTP id s11so612603oih.11 for ; Fri, 19 Jan 2018 22:58:45 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <151632009605.21271.11304291057104672116.stgit@dwillia2-desk3.amr.corp.intel.com> References: <151632009605.21271.11304291057104672116.stgit@dwillia2-desk3.amr.corp.intel.com> From: Dan Williams Date: Fri, 19 Jan 2018 22:58:44 -0800 Message-ID: Subject: Re: [PATCH v4 00/10] prevent bounds-check bypass via speculative execution Content-Type: text/plain; charset="UTF-8" Sender: linux-arch-owner@vger.kernel.org List-ID: To: Linux Kernel Mailing List Cc: Mark Rutland , Kernel Hardening , Peter Zijlstra , Catalin Marinas , Will Deacon , "H. Peter Anvin" , Elena Reshetova , linux-arch , Andi Kleen , Jonathan Corbet , X86 ML , Russell King , Ingo Molnar , Andrew Honig , Alan Cox , Tom Lendacky , Kees Cook , Al Viro , Andy Lutomirski , Thomas Gleixner , Andrew Morton , Jim Mattson , Christian Lamparter , Greg KH , Linux Wireless List , stable@vger.kernel.org, Paolo Bonzini , Johannes Berg , Linus Torvalds , "David S. Miller" Message-ID: <20180120065844.xX727UaxQ_K7nNpQwxJMLsKirEQk9Bp_Wv-nEnIf7xs@z> On Thu, Jan 18, 2018 at 4:01 PM, Dan Williams wrote: > Changes since v3 [1] > * Drop 'ifence_array_ptr' and associated compile-time + run-time > switching and just use the masking approach all the time. > > * Convert 'get_user' to use pointer sanitization via masking rather than > lfence. '__get_user' and associated paths still rely on > lfence. (Linus) > > "Basically, the rule is trivial: find all 'stac' users, and use > address masking if those users already integrate the limit > check, and lfence they don't." > > * At syscall entry sanitize the syscall number under speculation > to remove a user controlled pointer de-reference in kernel > space. (Linus) > > * Fix a raw lfence in the kvm code (added for v4.15-rc8) to use > 'array_ptr'. > > * Propose 'array_idx' as a way to sanitize user input that is > later used as an array index, but where the validation is > happening in a different code block than the array reference. > (Christian). > > * Fix grammar in speculation.txt (Kees) > > --- > > Quoting Mark's original RFC: > > "Recently, Google Project Zero discovered several classes of attack > against speculative execution. One of these, known as variant-1, allows > explicit bounds checks to be bypassed under speculation, providing an > arbitrary read gadget. Further details can be found on the GPZ blog [2] > and the Documentation patch in this series." > > A precondition of using this attack on the kernel is to get a user > controlled pointer de-referenced (under speculation) in privileged code. > The primary source of user controlled pointers in the kernel is the > arguments passed to 'get_user' and '__get_user'. An example of other > user controlled pointers are user-controlled array / pointer offsets. > > Better tooling is needed to find more arrays / pointers with user > controlled indices / offsets that can be converted to use 'array_ptr' or > 'array_idx'. A few are included in this set, and these are not expected > to be complete. That said, the 'get_user' protections raise the bar on > finding a vulnerable gadget in the kernel. > > These patches are also available via the 'nospec-v4' git branch here: > > git://git.kernel.org/pub/scm/linux/kernel/git/djbw/linux nospec-v4 I've pushed out a nospec-v4.1 with the below minor cleanup, a fixup of the changelog for "kvm, x86: fix spectre-v1 mitigation", and added Paolo's ack. git://git.kernel.org/pub/scm/linux/kernel/git/djbw/linux nospec-v4.1 diff --git a/include/linux/nospec.h b/include/linux/nospec.h index 8af35be1869e..b8a9222e34d1 100644 --- a/include/linux/nospec.h +++ b/include/linux/nospec.h @@ -37,7 +37,7 @@ static inline unsigned long array_ptr_mask(unsigned long idx, unsigned long sz) unsigned long _i = (idx); \ unsigned long _mask = array_ptr_mask(_i, (sz)); \ \ - __u._ptr = _arr + (_i & _mask); \ + __u._ptr = _arr + _i; \ __u._bit &= _mask; \ __u._ptr; \ })