From 1d4238c56f9816ce0f9c8dbe42d7f2ad81cb6613 Mon Sep 17 00:00:00 2001
From: Russell King <rmk+kernel@armlinux.org.uk>
Date: Fri, 11 May 2018 15:06:58 +0100
Subject: [PATCH] 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>
---
 arch/arm/include/asm/barrier.h | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/arm/include/asm/barrier.h b/arch/arm/include/asm/barrier.h
index 3d9c1d4b7e75..69772e742a0a 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__ */