1 files changed, 101 insertions, 0 deletions
diff --git a/arch/x86/mm/kmemcheck/opcode.c b/arch/x86/mm/kmemcheck/opcode.c
new file mode 100644
index 00000000000..a4100b6e783
--- /dev/null
+++ b/arch/x86/mm/kmemcheck/opcode.c
@@ -0,0 +1,101 @@
+#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;
+}
+
+#define REX_W (1 << 3)
+
+/*
+ * 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, unsigned int *size)
+{
+	/* Default operand size */
+	int operand_size_override = 4;
+
+	/* prefixes */
+	for (; opcode_is_prefix(*op); ++op) {
+		if (*op == 0x66)
+			operand_size_override = 2;
+	}
+
+#ifdef CONFIG_X86_64
+	/* REX prefix */
+	if (opcode_is_rex_prefix(*op)) {
+		uint8_t rex = *op;
+
+		++op;
+		if (rex & REX_W) {
+			switch (*op) {
+			case 0x63:
+				*size = 4;
+				return;
+			case 0x0f:
+				++op;
+
+				switch (*op) {
+				case 0xb6:
+				case 0xbe:
+					*size = 1;
+					return;
+				case 0xb7:
+				case 0xbf:
+					*size = 2;
+					return;
+				}
+
+				break;
+			}
+
+			*size = 8;
+			return;
+		}
+	}
+#endif
+
+	/* escape opcode */
+	if (*op == 0x0f) {
+		++op;
+
+		/*
+		 * This is move with zero-extend and sign-extend, respectively;
+		 * we don't have to think about 0xb6/0xbe, because this is
+		 * already handled in the conditional below.
+		 */
+		if (*op == 0xb7 || *op == 0xbf)
+			operand_size_override = 2;
+	}
+
+	*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;
+}