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 <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>

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 602af23b98c7856af4c7ee0473630b4866b3e54d..cf074bce3eb322c2ced7e3e05641f4c87d080ee0 100644 (file)
--- 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));
 }
 
 /**