1 files changed, 90 insertions, 0 deletions
diff --git a/arch/x86/mm/kmemcheck/opcode.c b/arch/x86/mm/kmemcheck/opcode.c
new file mode 100644
index 000000000000..88a9662e19aa
--- /dev/null
+++ b/arch/x86/mm/kmemcheck/opcode.c
@@ -0,0 +1,90 @@
+#include <linux/types.h>
+
+#include "opcode.h"
+
+static bool opcode_is_prefix(uint8_t b)
+{
+	return
+		/* Group 1 */
+		b == 0xf0 || b == 0xf2 || b == 0xf3
+		/* Group 2 */
+		|| b == 0x2e || b == 0x36 || b == 0x3e || b == 0x26
+		|| b == 0x64 || b == 0x65 || b == 0x2e || b == 0x3e
+		/* Group 3 */
+		|| b == 0x66
+		/* Group 4 */
+		|| b == 0x67;
+}
+
+static bool opcode_is_rex_prefix(uint8_t b)
+{
+	return (b & 0xf0) == 0x40;
+}
+
+/*
+ * This is a VERY crude opcode decoder. We only need to find the size of the
+ * load/store that caused our #PF and this should work for all the opcodes
+ * that we care about. Moreover, the ones who invented this instruction set
+ * should be shot.
+ */
+void kmemcheck_opcode_decode(const uint8_t *op,
+	const uint8_t **rep_prefix, const uint8_t **rex_prefix,
+	unsigned int *size)
+{
+	/* Default operand size */
+	int operand_size_override = 4;
+
+	*rep_prefix = NULL;
+
+	/* prefixes */
+	for (; opcode_is_prefix(*op); ++op) {
+		if (*op == 0xf2 || *op == 0xf3)
+			*rep_prefix = op;
+		if (*op == 0x66)
+			operand_size_override = 2;
+	}
+
+	*rex_prefix = NULL;
+
+#ifdef CONFIG_X86_64
+	/* REX prefix */
+	if (opcode_is_rex_prefix(*op)) {
+		*rex_prefix = op;
+
+		if (*op & 0x08) {
+			*size = 8;
+			return;
+		}
+
+		++op;
+	}
+#endif
+
+	/* escape opcode */
+	if (*op == 0x0f) {
+		++op;
+
+		if (*op == 0xb6) {
+			*size = 1;
+			return;
+		}
+
+		if (*op == 0xb7) {
+			*size = 2;
+			return;
+		}
+	}
+
+	*size = (*op & 1) ? operand_size_override : 1;
+}
+
+const uint8_t *kmemcheck_opcode_get_primary(const uint8_t *op)
+{
+	/* skip prefixes */
+	while (opcode_is_prefix(*op))
+		++op;
+	if (opcode_is_rex_prefix(*op))
+		++op;
+	return op;
+}
+