From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Cyrus-Session-Id: sloti22d1t05-3443661-1520826258-2-6031072194050151244 X-Sieve: CMU Sieve 3.0 X-Spam-known-sender: no X-Spam-score: 0.0 X-Spam-hits: BAYES_00 -1.9, HEADER_FROM_DIFFERENT_DOMAINS 0.25, ME_NOAUTH 0.01, RCVD_IN_DNSWL_HI -5, T_RP_MATCHES_RCVD -0.01, LANGUAGES en, BAYES_USED global, SA_VERSION 3.4.0 X-Spam-source: IP='209.132.180.67', Host='vger.kernel.org', Country='CN', FromHeader='uk', MailFrom='org' X-Spam-charsets: plain='UTF-8' X-Resolved-to: greg@kroah.com X-Delivered-to: greg@kroah.com X-Mail-from: stable-owner@vger.kernel.org ARC-Seal: i=1; a=rsa-sha256; cv=none; d=messagingengine.com; s=arctest; t=1520826257; b=PWYErE8QigO/NgwvmWNzhjQkuVlprcjXabIce/V+JRUVjgm G9kyp2jDGg5yv1KPCOY5kZm9wRzVpx537PIwlI2dAljzLBc9CzfjIeltEW3lGVNk AhLR2XW944hzTetvD4ynOhllXBxZEzdeM5zByghVwBVWBhsglkru72w7ipBlxjST o9QoktZtgE1Fnfwyc7ot5Tv548F+s/UnC90XsGYEbNUGz7XHL0sx35pYxgw8jgNB IOGZafrHdmF2AXrLK/bn5iJPcXvlOghIS+o+rsPMODUP7MolBdp78JFQmZuCVcOD Rjh+bsBRT2OsMOolIpA54gSNgW6q9VIt5ICi6tA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=content-type:content-transfer-encoding :mime-version:from:to:cc:date:message-id:subject:in-reply-to :sender:list-id; s=arctest; t=1520826257; bh=fu8Y2NWa4IHT2isvYtH Q89Ge0n3QMk7lXFafIXVgccc=; b=uciga4oKSjCC2tsK24s32YplaAQnyZHUf+K VKTFhVbQ3UkOD7SeVKI6OsNFUH4jXzVexrX2cLTY9nVSxEdXihPOuprbXFRLCeuN NdvC2J+xjnY373jfeNRFKEC6o/AFzWv+Oc9ogdSUNo+WYMRaussOlPMWcrkvpMhH plytA+DymTQUs1LJjZd9U2xkJckZwnncv5qddjUxHDtXTzGbp44sWgaFmdMlDZ4T pAB+S4/HEy0R3lJ+/7+IirQXp3VgbUsd2BNO2yLLcSNnW7qJOBJIcsDNVrZnsy4n g4GHwaJM0EHFJk8AAQb5HugVM343wbz+4eMPUrahEotxLB/fMxA== ARC-Authentication-Results: i=1; mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=decadent.org.uk; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-category=clean score=-100 state=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=decadent.org.uk header.result=pass header_is_org_domain=yes Authentication-Results: mx5.messagingengine.com; arc=none (no signatures found); dkim=none (no signatures found); dmarc=none (p=none,has-list-id=yes,d=none) header.from=decadent.org.uk; iprev=pass policy.iprev=209.132.180.67 (vger.kernel.org); spf=none smtp.mailfrom=stable-owner@vger.kernel.org smtp.helo=vger.kernel.org; x-aligned-from=fail; x-category=clean score=-100 state=0; x-ptr=pass x-ptr-helo=vger.kernel.org x-ptr-lookup=vger.kernel.org; x-return-mx=pass smtp.domain=vger.kernel.org smtp.result=pass smtp_org.domain=kernel.org smtp_org.result=pass smtp_is_org_domain=no header.domain=decadent.org.uk header.result=pass header_is_org_domain=yes Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932993AbeCLDl5 (ORCPT ); Sun, 11 Mar 2018 23:41:57 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:41152 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932657AbeCLDHm (ORCPT ); Sun, 11 Mar 2018 23:07:42 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "H. Peter Anvin" , "Andy Lutomirski" , "Borislav Petkov" , "Borislav Petkov" , "Denys Vlasenko" , "Thomas Gleixner" , "Oleg Nesterov" , "Ingo Molnar" , "Quentin Casasnovas" , "Linus Torvalds" , "Brian Gerst" Date: Mon, 12 Mar 2018 03:03:34 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 050/104] x86/alternatives: Fix ALTERNATIVE_2 padding generation properly In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: stable-owner@vger.kernel.org X-Mailing-List: stable@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: 3.2.101-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Borislav Petkov commit dbe4058a6a44af4ca5d146aebe01b0a1f9b7fd2a upstream. Quentin caught a corner case with the generation of instruction padding in the ALTERNATIVE_2 macro: if len(orig_insn) < len(alt1) < len(alt2), then not enough padding gets added and that is not good(tm) as we could overwrite the beginning of the next instruction. Luckily, at the time of this writing, we don't have ALTERNATIVE_2() invocations which have that problem and even if we did, a simple fix would be to prepend the instructions with enough prefixes so that that corner case doesn't happen. However, best it would be if we fixed it properly. See below for a simple, abstracted example of what we're doing. So what we ended up doing is, we compute the max(len(alt1), len(alt2)) - len(orig_insn) and feed that value to the .skip gas directive. The max() cannot have conditionals due to gas limitations, thus the fancy integer math. With this patch, all ALTERNATIVE_2 sites get padded correctly; generating obscure test cases pass too: #define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b))))) #define gen_skip(orig, alt1, alt2, marker) \ .skip -((alt_max_short(alt1, alt2) - (orig)) > 0) * \ (alt_max_short(alt1, alt2) - (orig)),marker .pushsection .text, "ax" .globl main main: gen_skip(1, 2, 4, 0x09) gen_skip(4, 1, 2, 0x10) ... .popsection Thanks to Quentin for catching it and double-checking the fix! Reported-by: Quentin Casasnovas Signed-off-by: Borislav Petkov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20150404133443.GE21152@pd.tnic Signed-off-by: Ingo Molnar Signed-off-by: Ben Hutchings --- arch/x86/include/asm/alternative-asm.h | 14 ++++++++++++-- arch/x86/include/asm/alternative.h | 16 ++++++++++++---- arch/x86/kernel/alternative.c | 4 ++-- 3 files changed, 26 insertions(+), 8 deletions(-) --- a/arch/x86/include/asm/alternative-asm.h +++ b/arch/x86/include/asm/alternative-asm.h @@ -45,12 +45,22 @@ .popsection .endm +#define old_len 141b-140b +#define new_len1 144f-143f +#define new_len2 145f-144f + +/* + * max without conditionals. Idea adapted from: + * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax + */ +#define alt_max_short(a, b) ((a) ^ (((a) ^ (b)) & -(-((a) < (b))))) + .macro ALTERNATIVE_2 oldinstr, newinstr1, feature1, newinstr2, feature2 140: \oldinstr 141: - .skip -(((144f-143f)-(141b-140b)) > 0) * ((144f-143f)-(141b-140b)),0x90 - .skip -(((145f-144f)-(144f-143f)-(141b-140b)) > 0) * ((145f-144f)-(144f-143f)-(141b-140b)),0x90 + .skip -((alt_max_short(new_len1, new_len2) - (old_len)) > 0) * \ + (alt_max_short(new_len1, new_len2) - (old_len)),0x90 142: .pushsection .altinstructions,"a" --- a/arch/x86/include/asm/alternative.h +++ b/arch/x86/include/asm/alternative.h @@ -95,13 +95,21 @@ static inline int alternatives_text_rese alt_end_marker ":\n" /* + * max without conditionals. Idea adapted from: + * http://graphics.stanford.edu/~seander/bithacks.html#IntegerMinOrMax + * + * The additional "-" is needed because gas works with s32s. + */ +#define alt_max_short(a, b) "((" a ") ^ (((" a ") ^ (" b ")) & -(-((" a ") - (" b ")))))" + +/* * Pad the second replacement alternative with additional NOPs if it is * additionally longer than the first replacement alternative. */ -#define OLDINSTR_2(oldinstr, num1, num2) \ - __OLDINSTR(oldinstr, num1) \ - ".skip -(((" alt_rlen(num2) ")-(" alt_rlen(num1) ")-(662b-661b)) > 0) * " \ - "((" alt_rlen(num2) ")-(" alt_rlen(num1) ")-(662b-661b)),0x90\n" \ +#define OLDINSTR_2(oldinstr, num1, num2) \ + "661:\n\t" oldinstr "\n662:\n" \ + ".skip -((" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")) > 0) * " \ + "(" alt_max_short(alt_rlen(num1), alt_rlen(num2)) " - (" alt_slen ")), 0x90\n" \ alt_end_marker ":\n" #define ALTINSTR_ENTRY(feature, num) \ --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -370,11 +370,11 @@ void __init_or_module apply_alternatives continue; } - DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d)", + DPRINTK("feat: %d*32+%d, old: (%p, len: %d), repl: (%p, len: %d), pad: %d", a->cpuid >> 5, a->cpuid & 0x1f, instr, a->instrlen, - replacement, a->replacementlen); + replacement, a->replacementlen, a->padlen); DUMP_BYTES(instr, a->instrlen, "%p: old_insn: ", instr); DUMP_BYTES(replacement, a->replacementlen, "%p: rpl_insn: ", replacement);