From: Rasmus Villemoes linux@rasmusvillemoes.dk
[ Upstream commit 7275b097851a5e2e0dd4da039c7e96b59ac5314e ]
The static inlines in bitmap.h do not handle a compile-time constant nbits==0 correctly (they dereference the passed src or dst pointers, despite only 0 words being valid to access). I had the 0-day buildbot chew on a patch [1] that would cause build failures for such cases without complaining, suggesting that we don't have any such users currently, at least for the 70 .config/arch combinations that was built. Should any turn up, make sure they use the out-of-line versions, which do handle nbits==0 correctly.
This is of course not the most efficient, but it's much less churn than teaching all the static inlines an "if (zero_const_nbits())", and since we don't have any current instances, this doesn't affect existing code at all.
[1] lkml.kernel.org/r/20180815085539.27485-1-linux@rasmusvillemoes.dk
Link: http://lkml.kernel.org/r/20180818131623.8755-3-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes linux@rasmusvillemoes.dk Reviewed-by: Andy Shevchenko andy.shevchenko@gmail.com Cc: Yury Norov ynorov@caviumnetworks.com Cc: Rasmus Villemoes linux@rasmusvillemoes.dk Cc: Sudeep Holla sudeep.holla@arm.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/bitmap.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index 9653fdb76a427..e9d5df4315d94 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -175,8 +175,13 @@ extern int bitmap_print_to_pagebuf(bool list, char *buf, #define BITMAP_FIRST_WORD_MASK(start) (~0UL << ((start) & (BITS_PER_LONG - 1))) #define BITMAP_LAST_WORD_MASK(nbits) (~0UL >> (-(nbits) & (BITS_PER_LONG - 1)))
+/* + * The static inlines below do not handle constant nbits==0 correctly, + * so make such users (should any ever turn up) call the out-of-line + * versions. + */ #define small_const_nbits(nbits) \ - (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG) + (__builtin_constant_p(nbits) && (nbits) <= BITS_PER_LONG && (nbits) > 0)
static inline void bitmap_zero(unsigned long *dst, unsigned int nbits) {