From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756309AbdESVfG (ORCPT ); Fri, 19 May 2017 17:35:06 -0400 Received: from shelob.surriel.com ([96.67.55.147]:35578 "EHLO shelob.surriel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752472AbdESVfC (ORCPT ); Fri, 19 May 2017 17:35:02 -0400 X-Greylist: delayed 496 seconds by postgrey-1.27 at vger.kernel.org; Fri, 19 May 2017 17:35:02 EDT From: riel@redhat.com To: linux-kernel@vger.kernel.org Cc: danielmicay@gmail.com, tytso@mit.edu, keescook@chromium.org, hpa@zytor.com, luto@amacapital.net, mingo@kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, catalin.marinas@arm.com, linux-sh@vger.kernel.org, ysato@users.sourceforge.jp Subject: [PATCH 1/5] random,stackprotect: introduce get_random_canary function Date: Fri, 19 May 2017 17:26:32 -0400 Message-Id: <20170519212636.30440-2-riel@redhat.com> X-Mailer: git-send-email 2.9.3 In-Reply-To: <20170519212636.30440-1-riel@redhat.com> References: <20170519212636.30440-1-riel@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Rik van Riel Introduce the get_random_canary function, which provides a random unsigned long canary value with the first byte zeroed out on 64 bit architectures, in order to mitigate non-terminated C string overflows. Inspired by the "ascii armor" code in the old execshield patches, and the current PaX/grsecurity code base. Signed-off-by: Rik van Riel --- include/linux/random.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) diff --git a/include/linux/random.h b/include/linux/random.h index ed5c3838780d..765a992c6774 100644 --- a/include/linux/random.h +++ b/include/linux/random.h @@ -57,6 +57,26 @@ static inline unsigned long get_random_long(void) #endif } +/* + * On 64 bit architectures, protect against non-terminated C string overflows + * by zeroing out the first byte of the canary; this leaves 56 bits of entropy. + */ +#ifdef CONFIG_64BIT +#ifdef __LITTLE_ENDIAN +#define CANARY_MASK 0xffffffffffffff00UL +#else /* big endian 64 bits */ +#define CANARY_MASK 0x00ffffffffffffffUL +#endif +#else /* 32 bits */ +#define CANARY_MASK 0xffffffffUL +#endif +static inline unsigned long get_random_canary(void) +{ + unsigned long val = get_random_long(); + + return val & CANARY_MASK; +} + unsigned long randomize_page(unsigned long start, unsigned long range); u32 prandom_u32(void); -- 2.9.3