1 #include <linux/types.h>
2 
3 #include "opcode.h"
4 
opcode_is_prefix(uint8_t b)5 static 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
opcode_is_rex_prefix(uint8_t b)20 static bool opcode_is_rex_prefix(uint8_t b)
21 {
22 	return (b & 0xf0) == 0x40;
23 }
24 #else
opcode_is_rex_prefix(uint8_t b)25 static 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  */
kmemcheck_opcode_decode(const uint8_t * op,unsigned int * size)39 void 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 
kmemcheck_opcode_get_primary(const uint8_t * op)98 const 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 }
107