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b2441318 | 1 | // SPDX-License-Identifier: GPL-2.0 |
dfec072e VN |
2 | #include <linux/types.h> |
3 | ||
4 | #include "opcode.h" | |
5 | ||
6 | static bool opcode_is_prefix(uint8_t b) | |
7 | { | |
8 | return | |
9 | /* Group 1 */ | |
10 | b == 0xf0 || b == 0xf2 || b == 0xf3 | |
11 | /* Group 2 */ | |
12 | || b == 0x2e || b == 0x36 || b == 0x3e || b == 0x26 | |
9fbaf49c | 13 | || b == 0x64 || b == 0x65 |
dfec072e VN |
14 | /* Group 3 */ |
15 | || b == 0x66 | |
16 | /* Group 4 */ | |
17 | || b == 0x67; | |
18 | } | |
19 | ||
6d9609c1 | 20 | #ifdef CONFIG_X86_64 |
dfec072e VN |
21 | static bool opcode_is_rex_prefix(uint8_t b) |
22 | { | |
23 | return (b & 0xf0) == 0x40; | |
24 | } | |
6d9609c1 PE |
25 | #else |
26 | static bool opcode_is_rex_prefix(uint8_t b) | |
27 | { | |
28 | return false; | |
29 | } | |
30 | #endif | |
dfec072e VN |
31 | |
32 | #define REX_W (1 << 3) | |
33 | ||
34 | /* | |
35 | * This is a VERY crude opcode decoder. We only need to find the size of the | |
36 | * load/store that caused our #PF and this should work for all the opcodes | |
37 | * that we care about. Moreover, the ones who invented this instruction set | |
38 | * should be shot. | |
39 | */ | |
40 | void kmemcheck_opcode_decode(const uint8_t *op, unsigned int *size) | |
41 | { | |
42 | /* Default operand size */ | |
43 | int operand_size_override = 4; | |
44 | ||
45 | /* prefixes */ | |
46 | for (; opcode_is_prefix(*op); ++op) { | |
47 | if (*op == 0x66) | |
48 | operand_size_override = 2; | |
49 | } | |
50 | ||
dfec072e VN |
51 | /* REX prefix */ |
52 | if (opcode_is_rex_prefix(*op)) { | |
53 | uint8_t rex = *op; | |
54 | ||
55 | ++op; | |
56 | if (rex & REX_W) { | |
57 | switch (*op) { | |
58 | case 0x63: | |
59 | *size = 4; | |
60 | return; | |
61 | case 0x0f: | |
62 | ++op; | |
63 | ||
64 | switch (*op) { | |
65 | case 0xb6: | |
66 | case 0xbe: | |
67 | *size = 1; | |
68 | return; | |
69 | case 0xb7: | |
70 | case 0xbf: | |
71 | *size = 2; | |
72 | return; | |
73 | } | |
74 | ||
75 | break; | |
76 | } | |
77 | ||
78 | *size = 8; | |
79 | return; | |
80 | } | |
81 | } | |
dfec072e VN |
82 | |
83 | /* escape opcode */ | |
84 | if (*op == 0x0f) { | |
85 | ++op; | |
86 | ||
87 | /* | |
88 | * This is move with zero-extend and sign-extend, respectively; | |
89 | * we don't have to think about 0xb6/0xbe, because this is | |
90 | * already handled in the conditional below. | |
91 | */ | |
92 | if (*op == 0xb7 || *op == 0xbf) | |
93 | operand_size_override = 2; | |
94 | } | |
95 | ||
96 | *size = (*op & 1) ? operand_size_override : 1; | |
97 | } | |
98 | ||
99 | const uint8_t *kmemcheck_opcode_get_primary(const uint8_t *op) | |
100 | { | |
101 | /* skip prefixes */ | |
102 | while (opcode_is_prefix(*op)) | |
103 | ++op; | |
104 | if (opcode_is_rex_prefix(*op)) | |
105 | ++op; | |
106 | return op; | |
107 | } |