From: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxxxxxx
Signed-off-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Reported-by: Ido Schimmel <idosch@xxxxxxxxxxxx>
Tested-by: Ido Schimmel <idosch@xxxxxxxxxxxx>
Reviewed-by: Will Deacon <will.deacon@xxxxxxx>
Cc: Vadim Pasternak <vadimp@xxxxxxxxxxxx>
Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
Cc: Jacek Anaszewski <jacek.anaszewski@xxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Matthias Kaehlcke <mka@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
include/linux/bitops.h | 16 ++++++++--------
1 file changed, 8 insertions(+), 8 deletions(-)
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -60,7 +60,7 @@ static __always_inline unsigned long hwe
*/
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, un
*/
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, un
*/
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, un
*/
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, un
*/
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, un
*/
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, un
*/
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, unsig
*/
static inline __u8 ror8(__u8 word, unsigned int shift)
{
- return (word >> shift) | (word << (8 - shift));
+ return (word >> (shift & 7)) | (word << ((-shift) & 7));
}
/**
