1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
|
/*
* Utility functions for x86 operand and address decoding
*
* Copyright (C) Intel Corporation 2017
*/
#include <linux/kernel.h>
#include <linux/string.h>
#include <linux/ratelimit.h>
#include <asm/inat.h>
#include <asm/insn.h>
#include <asm/insn-eval.h>
#undef pr_fmt
#define pr_fmt(fmt) "insn: " fmt
enum reg_type {
REG_TYPE_RM = 0,
REG_TYPE_INDEX,
REG_TYPE_BASE,
};
static int get_reg_offset(struct insn *insn, struct pt_regs *regs,
enum reg_type type)
{
int regno = 0;
static const int regoff[] = {
offsetof(struct pt_regs, ax),
offsetof(struct pt_regs, cx),
offsetof(struct pt_regs, dx),
offsetof(struct pt_regs, bx),
offsetof(struct pt_regs, sp),
offsetof(struct pt_regs, bp),
offsetof(struct pt_regs, si),
offsetof(struct pt_regs, di),
#ifdef CONFIG_X86_64
offsetof(struct pt_regs, r8),
offsetof(struct pt_regs, r9),
offsetof(struct pt_regs, r10),
offsetof(struct pt_regs, r11),
offsetof(struct pt_regs, r12),
offsetof(struct pt_regs, r13),
offsetof(struct pt_regs, r14),
offsetof(struct pt_regs, r15),
#endif
};
int nr_registers = ARRAY_SIZE(regoff);
/*
* Don't possibly decode a 32-bit instructions as
* reading a 64-bit-only register.
*/
if (IS_ENABLED(CONFIG_X86_64) && !insn->x86_64)
nr_registers -= 8;
switch (type) {
case REG_TYPE_RM:
regno = X86_MODRM_RM(insn->modrm.value);
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
case REG_TYPE_INDEX:
regno = X86_SIB_INDEX(insn->sib.value);
if (X86_REX_X(insn->rex_prefix.value))
regno += 8;
/*
* If ModRM.mod != 3 and SIB.index = 4 the scale*index
* portion of the address computation is null. This is
* true only if REX.X is 0. In such a case, the SIB index
* is used in the address computation.
*/
if (X86_MODRM_MOD(insn->modrm.value) != 3 && regno == 4)
return -EDOM;
break;
case REG_TYPE_BASE:
regno = X86_SIB_BASE(insn->sib.value);
/*
* If ModRM.mod is 0 and SIB.base == 5, the base of the
* register-indirect addressing is 0. In this case, a
* 32-bit displacement follows the SIB byte.
*/
if (!X86_MODRM_MOD(insn->modrm.value) && regno == 5)
return -EDOM;
if (X86_REX_B(insn->rex_prefix.value))
regno += 8;
break;
default:
pr_err_ratelimited("invalid register type: %d\n", type);
return -EINVAL;
}
if (regno >= nr_registers) {
WARN_ONCE(1, "decoded an instruction with an invalid register");
return -EINVAL;
}
return regoff[regno];
}
/**
* insn_get_modrm_rm_off() - Obtain register in r/m part of the ModRM byte
* @insn: Instruction containing the ModRM byte
* @regs: Register values as seen when entering kernel mode
*
* Returns:
*
* The register indicated by the r/m part of the ModRM byte. The
* register is obtained as an offset from the base of pt_regs. In specific
* cases, the returned value can be -EDOM to indicate that the particular value
* of ModRM does not refer to a register and shall be ignored.
*/
int insn_get_modrm_rm_off(struct insn *insn, struct pt_regs *regs)
{
return get_reg_offset(insn, regs, REG_TYPE_RM);
}
/*
* return the address being referenced be instruction
* for rm=3 returning the content of the rm reg
* for rm!=3 calculates the address using SIB and Disp
*/
void __user *insn_get_addr_ref(struct insn *insn, struct pt_regs *regs)
{
int addr_offset, base_offset, indx_offset;
unsigned long linear_addr = -1L;
long eff_addr, base, indx;
insn_byte_t sib;
insn_get_modrm(insn);
insn_get_sib(insn);
sib = insn->sib.value;
if (X86_MODRM_MOD(insn->modrm.value) == 3) {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out;
eff_addr = regs_get_register(regs, addr_offset);
} else {
if (insn->sib.nbytes) {
/*
* Negative values in the base and index offset means
* an error when decoding the SIB byte. Except -EDOM,
* which means that the registers should not be used
* in the address computation.
*/
base_offset = get_reg_offset(insn, regs, REG_TYPE_BASE);
if (base_offset == -EDOM)
base = 0;
else if (base_offset < 0)
goto out;
else
base = regs_get_register(regs, base_offset);
indx_offset = get_reg_offset(insn, regs, REG_TYPE_INDEX);
if (indx_offset == -EDOM)
indx = 0;
else if (indx_offset < 0)
goto out;
else
indx = regs_get_register(regs, indx_offset);
eff_addr = base + indx * (1 << X86_SIB_SCALE(sib));
} else {
addr_offset = get_reg_offset(insn, regs, REG_TYPE_RM);
if (addr_offset < 0)
goto out;
eff_addr = regs_get_register(regs, addr_offset);
}
eff_addr += insn->displacement.value;
}
linear_addr = (unsigned long)eff_addr;
out:
return (void __user *)linear_addr;
}
|
