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arm64: Implement array_index_mask_nospec()

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Provide an optimised, assembly implementation of array_index_mask_nospec()
for arm64 so that the compiler is not in a position to transform the code
in ways which affect its ability to inhibit speculation (e.g. by introducing
conditional branches).

This is similar to the sequence used by x86, modulo architectural differences
in the carry/borrow flags.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Robin Murphy 2018-02-05 15:34:17 +00:00 committed by Catalin Marinas
parent 669474e772
commit 022620eed3
1 changed files with 21 additions and 0 deletions
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21
arch/arm64/include/asm/barrier.h
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@ -41,6 +41,27 @@
#define dma_rmb() dmb(oshld)
#define dma_wmb() dmb(oshst)
/*
* Generate a mask for array_index__nospec() that is ~0UL when 0 <= idx < sz
* and 0 otherwise.
*/
#define array_index_mask_nospec array_index_mask_nospec
static inline unsigned long array_index_mask_nospec(unsigned long idx,
unsigned long sz)
{
unsigned long mask;
asm volatile(
" cmp %1, %2\n"
" sbc %0, xzr, xzr\n"
: "=r" (mask)
: "r" (idx), "Ir" (sz)
: "cc");
csdb();
return mask;
}
#define __smp_mb() dmb(ish)
#define __smp_rmb() dmb(ishld)
#define __smp_wmb() dmb(ishst)