1 files changed, 106 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..63c19e27aa6f
--- /dev/null
+++ b/arch/x86/mm/kmemcheck/opcode.c
@@ -0,0 +1,106 @@
+#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;
+}
+
+#ifdef CONFIG_X86_64
+static bool opcode_is_rex_prefix(uint8_t b)
+{
+        return (b & 0xf0) == 0x40;
+}
+#else
+static bool opcode_is_rex_prefix(uint8_t b)
+{
+        return false;
+}
+#endif
+
+#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;
+        }
+
+        /* 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;
+                }
+        }
+
+        /* 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;
+}