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1// SPDX-License-Identifier: GPL-2.0
2#include <linux/module.h>
3#include <linux/device.h>
4#include <linux/cpu.h>
5#include <asm/nospec-branch.h>
6
7int nobp = IS_ENABLED(CONFIG_KERNEL_NOBP);
8
9static int __init nobp_setup_early(char *str)
10{
11 bool enabled;
12 int rc;
13
14 rc = kstrtobool(str, &enabled);
15 if (rc)
16 return rc;
17 if (enabled && test_facility(82)) {
18 /*
19 * The user explicitly requested nobp=1, enable it and
20 * disable the expoline support.
21 */
22 nobp = 1;
23 if (IS_ENABLED(CONFIG_EXPOLINE))
24 nospec_disable = 1;
25 } else {
26 nobp = 0;
27 }
28 return 0;
29}
30early_param("nobp", nobp_setup_early);
31
32static int __init nospec_setup_early(char *str)
33{
34 nobp = 0;
35 return 0;
36}
37early_param("nospec", nospec_setup_early);
38
39static int __init nospec_report(void)
40{
41 if (test_facility(156))
42 pr_info("Spectre V2 mitigation: etokens\n");
43 if (nospec_uses_trampoline())
44 pr_info("Spectre V2 mitigation: execute trampolines\n");
45 if (nobp_enabled())
46 pr_info("Spectre V2 mitigation: limited branch prediction\n");
47 return 0;
48}
49arch_initcall(nospec_report);
50
51#ifdef CONFIG_EXPOLINE
52
53int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
54
55static int __init nospectre_v2_setup_early(char *str)
56{
57 nospec_disable = 1;
58 return 0;
59}
60early_param("nospectre_v2", nospectre_v2_setup_early);
61
62void __init nospec_auto_detect(void)
63{
64 if (test_facility(156) || cpu_mitigations_off()) {
65 /*
66 * The machine supports etokens.
67 * Disable expolines and disable nobp.
68 */
69 if (__is_defined(CC_USING_EXPOLINE))
70 nospec_disable = 1;
71 nobp = 0;
72 } else if (__is_defined(CC_USING_EXPOLINE)) {
73 /*
74 * The kernel has been compiled with expolines.
75 * Keep expolines enabled and disable nobp.
76 */
77 nospec_disable = 0;
78 nobp = 0;
79 }
80 /*
81 * If the kernel has not been compiled with expolines the
82 * nobp setting decides what is done, this depends on the
83 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
84 */
85}
86
87static int __init spectre_v2_setup_early(char *str)
88{
89 if (str && !strncmp(str, "on", 2)) {
90 nospec_disable = 0;
91 nobp = 0;
92 }
93 if (str && !strncmp(str, "off", 3))
94 nospec_disable = 1;
95 if (str && !strncmp(str, "auto", 4))
96 nospec_auto_detect();
97 return 0;
98}
99early_param("spectre_v2", spectre_v2_setup_early);
100
101static void __init_or_module __nospec_revert(s32 *start, s32 *end)
102{
103 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
104 static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 };
105 u8 *instr, *thunk, *br;
106 u8 insnbuf[6];
107 s32 *epo;
108
109 /* Second part of the instruction replace is always a nop */
110 memcpy(insnbuf + 2, branch, sizeof(branch));
111 for (epo = start; epo < end; epo++) {
112 instr = (u8 *) epo + *epo;
113 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
114 type = BRCL_EXPOLINE; /* brcl instruction */
115 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
116 type = BRASL_EXPOLINE; /* brasl instruction */
117 else
118 continue;
119 thunk = instr + (long)(*(int *)(instr + 2)) * 2;
120 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
121 /* exrl %r0,<target-br> */
122 br = thunk + (long)(*(int *)(thunk + 2)) * 2;
123 else
124 continue;
125 if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0)
126 continue;
127 switch (type) {
128 case BRCL_EXPOLINE:
129 /* brcl to thunk, replace with br + nop */
130 insnbuf[0] = br[0];
131 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
132 break;
133 case BRASL_EXPOLINE:
134 /* brasl to thunk, replace with basr + nop */
135 insnbuf[0] = 0x0d;
136 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
137 break;
138 }
139
140 s390_kernel_write(instr, insnbuf, 6);
141 }
142}
143
144void __init_or_module nospec_revert(s32 *start, s32 *end)
145{
146 if (nospec_disable)
147 __nospec_revert(start, end);
148}
149
150extern s32 __nospec_call_start[], __nospec_call_end[];
151extern s32 __nospec_return_start[], __nospec_return_end[];
152void __init nospec_init_branches(void)
153{
154 nospec_revert(__nospec_call_start, __nospec_call_end);
155 nospec_revert(__nospec_return_start, __nospec_return_end);
156}
157
158#endif /* CONFIG_EXPOLINE */
1// SPDX-License-Identifier: GPL-2.0
2#include <linux/module.h>
3#include <linux/device.h>
4#include <asm/nospec-branch.h>
5
6static int __init nobp_setup_early(char *str)
7{
8 bool enabled;
9 int rc;
10
11 rc = kstrtobool(str, &enabled);
12 if (rc)
13 return rc;
14 if (enabled && test_facility(82)) {
15 /*
16 * The user explicitely requested nobp=1, enable it and
17 * disable the expoline support.
18 */
19 __set_facility(82, S390_lowcore.alt_stfle_fac_list);
20 if (IS_ENABLED(CONFIG_EXPOLINE))
21 nospec_disable = 1;
22 } else {
23 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
24 }
25 return 0;
26}
27early_param("nobp", nobp_setup_early);
28
29static int __init nospec_setup_early(char *str)
30{
31 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
32 return 0;
33}
34early_param("nospec", nospec_setup_early);
35
36static int __init nospec_report(void)
37{
38 if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
39 pr_info("Spectre V2 mitigation: execute trampolines.\n");
40 if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
41 pr_info("Spectre V2 mitigation: limited branch prediction.\n");
42 return 0;
43}
44arch_initcall(nospec_report);
45
46#ifdef CONFIG_EXPOLINE
47
48int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
49
50static int __init nospectre_v2_setup_early(char *str)
51{
52 nospec_disable = 1;
53 return 0;
54}
55early_param("nospectre_v2", nospectre_v2_setup_early);
56
57void __init nospec_auto_detect(void)
58{
59 if (IS_ENABLED(CC_USING_EXPOLINE)) {
60 /*
61 * The kernel has been compiled with expolines.
62 * Keep expolines enabled and disable nobp.
63 */
64 nospec_disable = 0;
65 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
66 }
67 /*
68 * If the kernel has not been compiled with expolines the
69 * nobp setting decides what is done, this depends on the
70 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
71 */
72}
73
74static int __init spectre_v2_setup_early(char *str)
75{
76 if (str && !strncmp(str, "on", 2)) {
77 nospec_disable = 0;
78 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
79 }
80 if (str && !strncmp(str, "off", 3))
81 nospec_disable = 1;
82 if (str && !strncmp(str, "auto", 4))
83 nospec_auto_detect();
84 return 0;
85}
86early_param("spectre_v2", spectre_v2_setup_early);
87
88static void __init_or_module __nospec_revert(s32 *start, s32 *end)
89{
90 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
91 u8 *instr, *thunk, *br;
92 u8 insnbuf[6];
93 s32 *epo;
94
95 /* Second part of the instruction replace is always a nop */
96 for (epo = start; epo < end; epo++) {
97 instr = (u8 *) epo + *epo;
98 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
99 type = BRCL_EXPOLINE; /* brcl instruction */
100 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
101 type = BRASL_EXPOLINE; /* brasl instruction */
102 else
103 continue;
104 thunk = instr + (*(int *)(instr + 2)) * 2;
105 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
106 /* exrl %r0,<target-br> */
107 br = thunk + (*(int *)(thunk + 2)) * 2;
108 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
109 thunk[6] == 0x44 && thunk[7] == 0x00 &&
110 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
111 (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
112 /* larl %rx,<target br> + ex %r0,0(%rx) */
113 br = thunk + (*(int *)(thunk + 2)) * 2;
114 else
115 continue;
116 /* Check for unconditional branch 0x07f? or 0x47f???? */
117 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
118 continue;
119
120 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
121 switch (type) {
122 case BRCL_EXPOLINE:
123 insnbuf[0] = br[0];
124 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
125 if (br[0] == 0x47) {
126 /* brcl to b, replace with bc + nopr */
127 insnbuf[2] = br[2];
128 insnbuf[3] = br[3];
129 } else {
130 /* brcl to br, replace with bcr + nop */
131 }
132 break;
133 case BRASL_EXPOLINE:
134 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
135 if (br[0] == 0x47) {
136 /* brasl to b, replace with bas + nopr */
137 insnbuf[0] = 0x4d;
138 insnbuf[2] = br[2];
139 insnbuf[3] = br[3];
140 } else {
141 /* brasl to br, replace with basr + nop */
142 insnbuf[0] = 0x0d;
143 }
144 break;
145 }
146
147 s390_kernel_write(instr, insnbuf, 6);
148 }
149}
150
151void __init_or_module nospec_revert(s32 *start, s32 *end)
152{
153 if (nospec_disable)
154 __nospec_revert(start, end);
155}
156
157extern s32 __nospec_call_start[], __nospec_call_end[];
158extern s32 __nospec_return_start[], __nospec_return_end[];
159void __init nospec_init_branches(void)
160{
161 nospec_revert(__nospec_call_start, __nospec_call_end);
162 nospec_revert(__nospec_return_start, __nospec_return_end);
163}
164
165#endif /* CONFIG_EXPOLINE */