From ef4d6f6b275c498f8e5626c99dbeefdc5027f843 Mon Sep 17 00:00:00 2001 From: Rasmus Villemoes Date: Tue, 14 May 2019 15:43:27 -0700 Subject: include/linux/bitops.h: sanitize rotate primitives The ror32 implementation (word >> shift) | (word << (32 - shift) has undefined behaviour if shift is outside the [1, 31] range. Similarly for the 64 bit variants. Most callers pass a compile-time constant (naturally in that range), but there's an UBSAN report that these may actually be called with a shift count of 0. Instead of special-casing that, we can make them DTRT for all values of shift while also avoiding UB. For some reason, this was already partly done for rol32 (which was well-defined for [0, 31]). gcc 8 recognizes these patterns as rotates, so for example __u32 rol32(__u32 word, unsigned int shift) { return (word << (shift & 31)) | (word >> ((-shift) & 31)); } compiles to 0000000000000020 : 20: 89 f8 mov %edi,%eax 22: 89 f1 mov %esi,%ecx 24: d3 c0 rol %cl,%eax 26: c3 retq Older compilers unfortunately do not do as well, but this only affects the small minority of users that don't pass constants. Due to integer promotions, ro[lr]8 were already well-defined for shifts in [0, 8], and ro[lr]16 were mostly well-defined for shifts in [0, 16] (only mostly - u16 gets promoted to _signed_ int, so if bit 15 is set, word << 16 is undefined). For consistency, update those as well. Link: http://lkml.kernel.org/r/20190410211906.2190-1-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Reported-by: Ido Schimmel Tested-by: Ido Schimmel Reviewed-by: Will Deacon Cc: Vadim Pasternak Cc: Andrey Ryabinin Cc: Jacek Anaszewski Cc: Pavel Machek Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/bitops.h | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) (limited to 'include') diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 602af23b98c7..cf074bce3eb3 100644 --- a/include/linux/bitops.h +++ b/include/linux/bitops.h @@ -60,7 +60,7 @@ static __always_inline unsigned long hweight_long(unsigned long w) */ static inline __u64 rol64(__u64 word, unsigned int shift) { - return (word << shift) | (word >> (64 - shift)); + return (word << (shift & 63)) | (word >> ((-shift) & 63)); } /** @@ -70,7 +70,7 @@ static inline __u64 rol64(__u64 word, unsigned int shift) */ static inline __u64 ror64(__u64 word, unsigned int shift) { - return (word >> shift) | (word << (64 - shift)); + return (word >> (shift & 63)) | (word << ((-shift) & 63)); } /** @@ -80,7 +80,7 @@ static inline __u64 ror64(__u64 word, unsigned int shift) */ static inline __u32 rol32(__u32 word, unsigned int shift) { - return (word << shift) | (word >> ((-shift) & 31)); + return (word << (shift & 31)) | (word >> ((-shift) & 31)); } /** @@ -90,7 +90,7 @@ static inline __u32 rol32(__u32 word, unsigned int shift) */ static inline __u32 ror32(__u32 word, unsigned int shift) { - return (word >> shift) | (word << (32 - shift)); + return (word >> (shift & 31)) | (word << ((-shift) & 31)); } /** @@ -100,7 +100,7 @@ static inline __u32 ror32(__u32 word, unsigned int shift) */ static inline __u16 rol16(__u16 word, unsigned int shift) { - return (word << shift) | (word >> (16 - shift)); + return (word << (shift & 15)) | (word >> ((-shift) & 15)); } /** @@ -110,7 +110,7 @@ static inline __u16 rol16(__u16 word, unsigned int shift) */ static inline __u16 ror16(__u16 word, unsigned int shift) { - return (word >> shift) | (word << (16 - shift)); + return (word >> (shift & 15)) | (word << ((-shift) & 15)); } /** @@ -120,7 +120,7 @@ static inline __u16 ror16(__u16 word, unsigned int shift) */ static inline __u8 rol8(__u8 word, unsigned int shift) { - return (word << shift) | (word >> (8 - shift)); + return (word << (shift & 7)) | (word >> ((-shift) & 7)); } /** @@ -130,7 +130,7 @@ static inline __u8 rol8(__u8 word, unsigned int shift) */ static inline __u8 ror8(__u8 word, unsigned int shift) { - return (word >> shift) | (word << (8 - shift)); + return (word >> (shift & 7)) | (word << ((-shift) & 7)); } /** -- cgit