From: Rasmus Villemoes linux@rasmusvillemoes.dk
commit ef4d6f6b275c498f8e5626c99dbeefdc5027f843 upstream.
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 <rol32>: 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 linux@rasmusvillemoes.dk Reported-by: Ido Schimmel idosch@mellanox.com Tested-by: Ido Schimmel idosch@mellanox.com Reviewed-by: Will Deacon will.deacon@arm.com Cc: Vadim Pasternak vadimp@mellanox.com Cc: Andrey Ryabinin aryabinin@virtuozzo.com Cc: Jacek Anaszewski jacek.anaszewski@gmail.com Cc: Pavel Machek pavel@ucw.cz Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Matthias Kaehlcke mka@chromium.org --- Hi Greg and Sasha,
Please pick this patch for 4.19. It fixes (at least) crashes due to undefined instructions in BPF code on arm32 when building with clang:
[ 4.271668] Internal error: Oops - undefined instruction: 0 [#1] PREEMPT SMP ARM [ 4.271675] Modules linked in: [ 4.284143] joydev [ 4.284155] CPU: 2 PID: 279 Comm: udevd Not tainted 4.19.44 #95 [ 4.284157] Hardware name: Rockchip (Device Tree) [ 4.284167] PC is at 0xbf017de8 [ 4.284176] LR is at sk_filter_trim_cap+0xfc/0x244 [ 4.284181] pc : [<bf017de8>] lr : [<c0890c34>] psr: 60070013 [ 4.323863] sp : ed36fcd8 ip : 00000000 fp : ed36fd28 [ 4.329698] r10: c100b608 r9 : 00000000 r8 : ed2d6600 [ 4.335531] r7 : 00000000 r6 : 00000071 r5 : 00000000 r4 : ed59c180 [ 4.342812] r3 : 00000000 r2 : ed59c180 r1 : 00000000 r0 : 2a1884a1 [ 4.350105] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment none [ 4.358075] Control: 30c5387d Table: 2d22b880 DAC: 44541fd3 [ 4.364495] Process udevd (pid: 279, stack limit = 0xb5b8ffdf) [ 4.371009] Stack: (0xed36fcd8 to 0xed370000) [ 4.375864] fcc0: bf017a9c 60070013 [ 4.385001] fce0: 00000000 00000000 ed36fcd8 00000000 00000089 00000000 ed2d6600 00000000 [ 4.394137] fd00: 00000000 00000000 ed59c180 f0c12000 00000000 ed289000 ed59c1a0 00000001 [ 4.403274] fd20: 00000071 00000000 ed59c180 f0c12000 00000000 ed289000 ed59c1a0 00000001 ... [ 4.613384] [<c0890c34>] (sk_filter_trim_cap) from [<00000001>] (0x1) [ 4.620580] Code: aa000002 e0200000 e3a01000 ea000045 (f7e6c179)
Thanks
Matthias --- include/linux/bitops.h | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-)
diff --git a/include/linux/bitops.h b/include/linux/bitops.h index 7ddb1349394d..7ac2e46112b7 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)); }
/**