From mboxrd@z Thu Jan 1 00:00:00 1970 From: riel@redhat.com Date: Fri, 19 May 2017 21:26:32 +0000 Subject: [PATCH 1/5] random,stackprotect: introduce get_random_canary function Message-Id: <20170519212636.30440-2-riel@redhat.com> List-Id: References: <20170519212636.30440-1-riel@redhat.com> In-Reply-To: <20170519212636.30440-1-riel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-arm-kernel@lists.infradead.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