Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1030501AbdDZVVj (ORCPT ); Wed, 26 Apr 2017 17:21:39 -0400 Received: from mail-it0-f47.google.com ([209.85.214.47]:37231 "EHLO mail-it0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1030473AbdDZVV1 (ORCPT ); Wed, 26 Apr 2017 17:21:27 -0400 MIME-Version: 1.0 In-Reply-To: <02F6E6C7-5AC0-431A-9008-DBDB4EFC1A6D@zytor.com> References: <20170426205504.133693-1-mka@chromium.org> <02F6E6C7-5AC0-431A-9008-DBDB4EFC1A6D@zytor.com> From: Kees Cook Date: Wed, 26 Apr 2017 14:21:25 -0700 X-Google-Sender-Auth: yMH_JKvYd-TaVGUSlzPlJG_lafk Message-ID: Subject: Re: [PATCH v2] x86/mm/kaslr: Use _ASM_MUL macro for multiplication To: "H. Peter Anvin" Cc: Matthias Kaehlcke , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , LKML , Grant Grundler , Greg Hackmann , Michael Davidson 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: 2286 Lines: 70 On Wed, Apr 26, 2017 at 2:00 PM, wrote: > On April 26, 2017 1:55:04 PM PDT, Matthias Kaehlcke wrote: >>In difference to gas clang doesn't seem to infer the size from the >>operands. Add and use the _ASM_MUL macro which determines the operand >>size and resolves to the 'mul' instruction with the corresponding >>suffix. >> >>This fixes the following error when building with clang: >> >>CC arch/x86/lib/kaslr.o >>/tmp/kaslr-dfe1ad.s: Assembler messages: >>/tmp/kaslr-dfe1ad.s:182: Error: no instruction mnemonic suffix given >>and >>no register operands; can't size instruction >> >>Signed-off-by: Matthias Kaehlcke >>--- >>Changes in v2: >>- use _ASM_MUL instead of #ifdef >>- updated commit message >> >> arch/x86/include/asm/asm.h | 1 + >> arch/x86/lib/kaslr.c | 3 ++- >> 2 files changed, 3 insertions(+), 1 deletion(-) >> >>diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h >>index 7acb51c49fec..7a9df3beb89b 100644 >>--- a/arch/x86/include/asm/asm.h >>+++ b/arch/x86/include/asm/asm.h >>@@ -32,6 +32,7 @@ >> #define _ASM_ADD __ASM_SIZE(add) >> #define _ASM_SUB __ASM_SIZE(sub) >> #define _ASM_XADD __ASM_SIZE(xadd) >>+#define _ASM_MUL __ASM_SIZE(mul) >> >> #define _ASM_AX __ASM_REG(ax) >> #define _ASM_BX __ASM_REG(bx) >>diff --git a/arch/x86/lib/kaslr.c b/arch/x86/lib/kaslr.c >>index 121f59c6ee54..0c7fe444dcdd 100644 >>--- a/arch/x86/lib/kaslr.c >>+++ b/arch/x86/lib/kaslr.c >>@@ -5,6 +5,7 @@ >> * kernel starts. This file is included in the compressed kernel and >> * normally linked in the regular. >> */ >>+#include >> #include >> #include >> #include >>@@ -79,7 +80,7 @@ unsigned long kaslr_get_random_long(const char >>*purpose) >> } >> >> /* Circular multiply for better bit diffusion */ >>- asm("mul %3" >>+ asm(_ASM_MUL "%3" >> : "=a" (random), "=d" (raw) >> : "a" (random), "rm" (mix_const)); >> random += raw; > > This really feels like a "fix your compiler" issue. We already use the other forms, what's so bad about adding mul too? And if this lets us build under clang, all the better. -Kees -- Kees Cook Pixel Security