1#include <linux/types.h>
  2
  3#include "opcode.h"
  4
  5static bool opcode_is_prefix(uint8_t b)
  6{
  7	return
  8		/* Group 1 */
  9		b == 0xf0 || b == 0xf2 || b == 0xf3
 10		/* Group 2 */
 11		|| b == 0x2e || b == 0x36 || b == 0x3e || b == 0x26
 12		|| b == 0x64 || b == 0x65
 13		/* Group 3 */
 14		|| b == 0x66
 15		/* Group 4 */
 16		|| b == 0x67;
 17}
 18
 19#ifdef CONFIG_X86_64
 20static bool opcode_is_rex_prefix(uint8_t b)
 21{
 22	return (b & 0xf0) == 0x40;
 23}
 24#else
 25static bool opcode_is_rex_prefix(uint8_t b)
 26{
 27	return false;
 28}
 29#endif
 30
 31#define REX_W (1 << 3)
 32
 33/*
 34 * This is a VERY crude opcode decoder. We only need to find the size of the
 35 * load/store that caused our #PF and this should work for all the opcodes
 36 * that we care about. Moreover, the ones who invented this instruction set
 37 * should be shot.
 38 */
 39void kmemcheck_opcode_decode(const uint8_t *op, unsigned int *size)
 40{
 41	/* Default operand size */
 42	int operand_size_override = 4;
 43
 44	/* prefixes */
 45	for (; opcode_is_prefix(*op); ++op) {
 46		if (*op == 0x66)
 47			operand_size_override = 2;
 48	}
 49
 50	/* REX prefix */
 51	if (opcode_is_rex_prefix(*op)) {
 52		uint8_t rex = *op;
 53
 54		++op;
 55		if (rex & REX_W) {
 56			switch (*op) {
 57			case 0x63:
 58				*size = 4;
 59				return;
 60			case 0x0f:
 61				++op;
 62
 63				switch (*op) {
 64				case 0xb6:
 65				case 0xbe:
 66					*size = 1;
 67					return;
 68				case 0xb7:
 69				case 0xbf:
 70					*size = 2;
 71					return;
 72				}
 73
 74				break;
 75			}
 76
 77			*size = 8;
 78			return;
 79		}
 80	}
 81
 82	/* escape opcode */
 83	if (*op == 0x0f) {
 84		++op;
 85
 86		/*
 87		 * This is move with zero-extend and sign-extend, respectively;
 88		 * we don't have to think about 0xb6/0xbe, because this is
 89		 * already handled in the conditional below.
 90		 */
 91		if (*op == 0xb7 || *op == 0xbf)
 92			operand_size_override = 2;
 93	}
 94
 95	*size = (*op & 1) ? operand_size_override : 1;
 96}
 97
 98const uint8_t *kmemcheck_opcode_get_primary(const uint8_t *op)
 99{
100	/* skip prefixes */
101	while (opcode_is_prefix(*op))
102		++op;
103	if (opcode_is_rex_prefix(*op))
104		++op;
105	return op;
106}