[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] x86+Arm32: make find_next_{, zero_}bit() have well defined behavior
commit 7442006b9f0940fb36f1f8470a416ec836e0d2ce Author: Jan Beulich <jbeulich@xxxxxxxx> AuthorDate: Wed Dec 11 14:06:18 2019 +0100 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Wed Dec 11 14:06:18 2019 +0100 x86+Arm32: make find_next_{,zero_}bit() have well defined behavior These functions getting used with the 2nd and 3rd arguments being equal wasn't well defined: Arm64 reliably returns the value of the 2nd argument in this case, while on x86 for bitmaps up to 64 bits wide the return value was undefined (due to the undefined behavior of a shift of a value by the number of bits it's wide) when the incoming value was 64. On Arm32 an actual out of bounds access would happen when the size/offset value is a multiple of 32; if this access doesn't fault, the return value would have been sufficiently correct afaict. Make the functions consistently tolerate the last two arguments being equal (and in fact the 3rd argument being greater or equal to the 2nd), in favor of finding and fixing all the use sites that violate the original more strict assumption. This is XSA-307. Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> Acked-by: Julien Grall <julien@xxxxxxx> --- xen/arch/arm/arm32/lib/findbit.S | 16 ++++++++-------- xen/include/asm-x86/bitops.h | 4 ++-- 2 files changed, 10 insertions(+), 10 deletions(-) diff --git a/xen/arch/arm/arm32/lib/findbit.S b/xen/arch/arm/arm32/lib/findbit.S index b4e219a8d7..00674a31ef 100644 --- a/xen/arch/arm/arm32/lib/findbit.S +++ b/xen/arch/arm/arm32/lib/findbit.S @@ -42,8 +42,8 @@ ENDPROC(_find_first_zero_bit_le) * Prototype: int find_next_zero_bit(void *addr, unsigned int maxbit, int offset) */ ENTRY(_find_next_zero_bit_le) - teq r1, #0 - beq 3b + cmp r1, r2 + bls 3b ands ip, r2, #7 beq 1b @ If new byte, goto old routine ARM( ldrb r3, [r0, r2, lsr #3] ) @@ -83,8 +83,8 @@ ENDPROC(_find_first_bit_le) * Prototype: int find_next_zero_bit(void *addr, unsigned int maxbit, int offset) */ ENTRY(_find_next_bit_le) - teq r1, #0 - beq 3b + cmp r1, r2 + bls 3b ands ip, r2, #7 beq 1b @ If new byte, goto old routine ARM( ldrb r3, [r0, r2, lsr #3] ) @@ -117,8 +117,8 @@ ENTRY(_find_first_zero_bit_be) ENDPROC(_find_first_zero_bit_be) ENTRY(_find_next_zero_bit_be) - teq r1, #0 - beq 3b + cmp r1, r2 + bls 3b ands ip, r2, #7 beq 1b @ If new byte, goto old routine eor r3, r2, #0x18 @ big endian byte ordering @@ -151,8 +151,8 @@ ENTRY(_find_first_bit_be) ENDPROC(_find_first_bit_be) ENTRY(_find_next_bit_be) - teq r1, #0 - beq 3b + cmp r1, r2 + bls 3b ands ip, r2, #7 beq 1b @ If new byte, goto old routine eor r3, r2, #0x18 @ big endian byte ordering diff --git a/xen/include/asm-x86/bitops.h b/xen/include/asm-x86/bitops.h index e66d861080..5a71afbc89 100644 --- a/xen/include/asm-x86/bitops.h +++ b/xen/include/asm-x86/bitops.h @@ -358,7 +358,7 @@ static always_inline unsigned int __scanbit(unsigned long val, unsigned int max) const unsigned long *a__ = (addr); \ unsigned int s__ = (size); \ unsigned int o__ = (off); \ - if ( __builtin_constant_p(size) && !s__ ) \ + if ( o__ >= s__ ) \ r__ = s__; \ else if ( __builtin_constant_p(size) && s__ <= BITS_PER_LONG ) \ r__ = o__ + __scanbit(*(const unsigned long *)(a__) >> o__, s__); \ @@ -390,7 +390,7 @@ static always_inline unsigned int __scanbit(unsigned long val, unsigned int max) const unsigned long *a__ = (addr); \ unsigned int s__ = (size); \ unsigned int o__ = (off); \ - if ( __builtin_constant_p(size) && !s__ ) \ + if ( o__ >= s__ ) \ r__ = s__; \ else if ( __builtin_constant_p(size) && s__ <= BITS_PER_LONG ) \ r__ = o__ + __scanbit(~*(const unsigned long *)(a__) >> o__, s__); \ -- generated by git-patchbot for /home/xen/git/xen.git#master _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/xen-changelog
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