Commit 022620ee authored Feb 05, 2018 by Robin Murphy Committed by Catalin Marinas Feb 06, 2018

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 <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>

parent 669474e7

arch/arm64/include/asm/barrier.h

+21 −0

Original line number	Diff line number	Diff line
		@@ -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)

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