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
|
// SPDX-License-Identifier: GPL-2.0
#include <linux/module.h>
#include <linux/device.h>
#include <asm/nospec-branch.h>
static int __init nobp_setup_early(char *str)
{
bool enabled;
int rc;
rc = kstrtobool(str, &enabled);
if (rc)
return rc;
if (enabled && test_facility(82)) {
/*
* The user explicitely requested nobp=1, enable it and
* disable the expoline support.
*/
__set_facility(82, S390_lowcore.alt_stfle_fac_list);
if (IS_ENABLED(CONFIG_EXPOLINE))
nospec_disable = 1;
} else {
__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
}
return 0;
}
early_param("nobp", nobp_setup_early);
static int __init nospec_setup_early(char *str)
{
__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
return 0;
}
early_param("nospec", nospec_setup_early);
static int __init nospec_report(void)
{
if (test_facility(156))
pr_info("Spectre V2 mitigation: etokens\n");
if (__is_defined(CC_USING_EXPOLINE) && !nospec_disable)
pr_info("Spectre V2 mitigation: execute trampolines\n");
if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
pr_info("Spectre V2 mitigation: limited branch prediction\n");
return 0;
}
arch_initcall(nospec_report);
#ifdef CONFIG_EXPOLINE
int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
static int __init nospectre_v2_setup_early(char *str)
{
nospec_disable = 1;
return 0;
}
early_param("nospectre_v2", nospectre_v2_setup_early);
void __init nospec_auto_detect(void)
{
if (test_facility(156)) {
/*
* The machine supports etokens.
* Disable expolines and disable nobp.
*/
if (__is_defined(CC_USING_EXPOLINE))
nospec_disable = 1;
__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
} else if (__is_defined(CC_USING_EXPOLINE)) {
/*
* The kernel has been compiled with expolines.
* Keep expolines enabled and disable nobp.
*/
nospec_disable = 0;
__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
}
/*
* If the kernel has not been compiled with expolines the
* nobp setting decides what is done, this depends on the
* CONFIG_KERNEL_NP option and the nobp/nospec parameters.
*/
}
static int __init spectre_v2_setup_early(char *str)
{
if (str && !strncmp(str, "on", 2)) {
nospec_disable = 0;
__clear_facility(82, S390_lowcore.alt_stfle_fac_list);
}
if (str && !strncmp(str, "off", 3))
nospec_disable = 1;
if (str && !strncmp(str, "auto", 4))
nospec_auto_detect();
return 0;
}
early_param("spectre_v2", spectre_v2_setup_early);
static void __init_or_module __nospec_revert(s32 *start, s32 *end)
{
enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
u8 *instr, *thunk, *br;
u8 insnbuf[6];
s32 *epo;
/* Second part of the instruction replace is always a nop */
for (epo = start; epo < end; epo++) {
instr = (u8 *) epo + *epo;
if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
type = BRCL_EXPOLINE; /* brcl instruction */
else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
type = BRASL_EXPOLINE; /* brasl instruction */
else
continue;
thunk = instr + (*(int *)(instr + 2)) * 2;
if (thunk[0] == 0xc6 && thunk[1] == 0x00)
/* exrl %r0,<target-br> */
br = thunk + (*(int *)(thunk + 2)) * 2;
else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
thunk[6] == 0x44 && thunk[7] == 0x00 &&
(thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
(thunk[1] & 0xf0) == (thunk[8] & 0xf0))
/* larl %rx,<target br> + ex %r0,0(%rx) */
br = thunk + (*(int *)(thunk + 2)) * 2;
else
continue;
/* Check for unconditional branch 0x07f? or 0x47f???? */
if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
continue;
memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
switch (type) {
case BRCL_EXPOLINE:
insnbuf[0] = br[0];
insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
if (br[0] == 0x47) {
/* brcl to b, replace with bc + nopr */
insnbuf[2] = br[2];
insnbuf[3] = br[3];
} else {
/* brcl to br, replace with bcr + nop */
}
break;
case BRASL_EXPOLINE:
insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
if (br[0] == 0x47) {
/* brasl to b, replace with bas + nopr */
insnbuf[0] = 0x4d;
insnbuf[2] = br[2];
insnbuf[3] = br[3];
} else {
/* brasl to br, replace with basr + nop */
insnbuf[0] = 0x0d;
}
break;
}
s390_kernel_write(instr, insnbuf, 6);
}
}
void __init_or_module nospec_revert(s32 *start, s32 *end)
{
if (nospec_disable)
__nospec_revert(start, end);
}
extern s32 __nospec_call_start[], __nospec_call_end[];
extern s32 __nospec_return_start[], __nospec_return_end[];
void __init nospec_init_branches(void)
{
nospec_revert(__nospec_call_start, __nospec_call_end);
nospec_revert(__nospec_return_start, __nospec_return_end);
}
#endif /* CONFIG_EXPOLINE */
|
