Commit ec70e2c1 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Greg Kroah-Hartman

include/linux/bitops.h: sanitize rotate primitives

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.dkSigned-off-by: default avatarRasmus Villemoes <linux@rasmusvillemoes.dk>
Reported-by: default avatarIdo Schimmel <idosch@mellanox.com>
Tested-by: default avatarIdo Schimmel <idosch@mellanox.com>
Reviewed-by: default avatarWill 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarMatthias Kaehlcke <mka@chromium.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fbbc4fe0
......@@ -68,7 +68,7 @@ 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));
}
/**
......@@ -78,7 +78,7 @@ 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));
}
/**
......@@ -88,7 +88,7 @@ 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));
}
/**
......@@ -98,7 +98,7 @@ 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));
}
/**
......@@ -108,7 +108,7 @@ 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));
}
/**
......@@ -118,7 +118,7 @@ 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));
}
/**
......@@ -128,7 +128,7 @@ 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));
}
/**
......@@ -138,7 +138,7 @@ 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));
}
/**
......
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