ARM: spectre-v1: add array_index_mask_nospec() implementation
Add an implementation of the array_index_mask_nospec() function for
mitigating Spectre variant 1 throughout the kernel.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Boot-tested-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h
index 3d9c1d4..69772e7 100644
--- a/arch/arm/include/asm/barrier.h
+++ b/arch/arm/include/asm/barrier.h
@@ -76,6 +76,25 @@ extern void arm_heavy_mb(void);
#define __smp_rmb() __smp_mb()
#define __smp_wmb() dmb(ishst)
+#ifdef CONFIG_CPU_SPECTRE
+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, %1, %1\n"
+ CSDB
+ : "=r" (mask)
+ : "r" (idx), "Ir" (sz)
+ : "cc");
+
+ return mask;
+}
+#define array_index_mask_nospec array_index_mask_nospec
+#endif
+
#include <asm-generic/barrier.h>
#endif /* !__ASSEMBLY__ */
