From 47c491d79cde198361bdaa3707be84a3a5dbba14 Mon Sep 17 00:00:00 2001 From: Robin Murphy Date: Mon, 5 Feb 2018 15:34:17 +0000 Subject: arm64: Implement array_index_mask_nospec() commit 022620eed3d0 upstream. 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 Signed-off-by: Alex Shi --- arch/arm64/include/asm/barrier.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) diff --git a/arch/arm64/include/asm/barrier.h b/arch/arm64/include/asm/barrier.h index c68fdc5707ed..0b0755c961ac 100644 --- a/arch/arm64/include/asm/barrier.h +++ b/arch/arm64/include/asm/barrier.h @@ -40,6 +40,27 @@ #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) -- cgit v1.2.3