Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756605Ab3DZPbB (ORCPT ); Fri, 26 Apr 2013 11:31:01 -0400 Received: from mail-oa0-f54.google.com ([209.85.219.54]:59212 "EHLO mail-oa0-f54.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754073Ab3DZPbA (ORCPT ); Fri, 26 Apr 2013 11:31:00 -0400 MIME-Version: 1.0 In-Reply-To: References: <1366926860-26776-1-git-send-email-keescook@chromium.org> <1366926860-26776-5-git-send-email-keescook@chromium.org> Date: Fri, 26 Apr 2013 08:30:59 -0700 X-Google-Sender-Auth: tiz0ePbM-_ZBcYl_SfLkNF_uTDc Message-ID: Subject: Re: [kernel-hardening] [PATCH 4/6] x86: kaslr: select random base offset From: Kees Cook To: Mathias Krause Cc: "linux-kernel@vger.kernel.org" , "kernel-hardening@lists.openwall.com" , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , "x86@kernel.org" , Jarkko Sakkinen , Matthew Garrett , Matt Fleming , Eric Northup , Dan Rosenberg , Julien Tinnes , Will Drewry Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1973 Lines: 61 On Thu, Apr 25, 2013 at 11:13 PM, Mathias Krause wrote: > On Thu, Apr 25, 2013 at 11:54 PM, Kees Cook wrote: >> Select a random location when CONFIG_RANDOMIZE_BASE is used, bounded >> by CONFIG_RANDOMIZE_BASE_MAX_OFFSET. Sources of randomness currently >> include RDRAND and RDTSC. >> >> Signed-off-by: Kees Cook >> --- >> arch/x86/Kconfig | 29 +++++++++++++-- >> arch/x86/boot/compressed/aslr.c | 75 +++++++++++++++++++++++++++++++++++++-- >> 2 files changed, 100 insertions(+), 4 deletions(-) >> >> [snip] >> >> diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c >> index d5331ee..11a91c6 100644 >> --- a/arch/x86/boot/compressed/aslr.c >> +++ b/arch/x86/boot/compressed/aslr.c >> @@ -2,18 +2,89 @@ >> >> #ifdef CONFIG_RANDOMIZE_BASE >> >> +#include >> +static inline int rdrand(unsigned long *v) >> +{ >> + int ok; >> + asm volatile("1: " RDRAND_LONG "\n\t" >> + "jc 2f\n\t" >> + "decl %0\n\t" >> + "jnz 1b\n\t" >> + "2:" >> + : "=r" (ok), "=a" (*v) >> + : "0" (RDRAND_RETRY_LOOPS)); >> + return ok; >> +} >> + >> +static inline uint32_t rdtsc(void) >> +{ >> + uint32_t timer; >> + >> + asm volatile("rdtsc\n" : "=a" (timer)); > > '\n' in the assembly statement is not needed. Also, RDTSC trashes > edx/rdx as well so it should be mentioned in the clobber list, at > least. > Maybe using rdtscl() from instead is an option? Ah yeah, rdtscl is perfect. I'll use that instead. Thanks! -Kees -- Kees Cook Chrome OS Security -- 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/