From: Robin Murphy Date: Mon, 5 Feb 2018 15:34:17 +0000 (+0000) Subject: arm64: Implement array_index_mask_nospec() X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=022620eed3d0bc4bf2027326f599f5ad71c2ea3f;p=linux.git arm64: Implement array_index_mask_nospec() 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 Signed-off-by: Robin Murphy Signed-off-by: Will Deacon Signed-off-by: Catalin Marinas --- diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index c0a846d2c6022..f11518af96a93 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -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)