s390/speculation: Support 'mitigations=' cmdline option
[sfrench/cifs-2.6.git] / arch / s390 / kernel / nospec-branch.c
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
7 static int __init nobp_setup_early(char *str)
8 {
9         bool enabled;
10         int rc;
11
12         rc = kstrtobool(str, &enabled);
13         if (rc)
14                 return rc;
15         if (enabled && test_facility(82)) {
16                 /*
17                  * The user explicitely requested nobp=1, enable it and
18                  * disable the expoline support.
19                  */
20                 __set_facility(82, S390_lowcore.alt_stfle_fac_list);
21                 if (IS_ENABLED(CONFIG_EXPOLINE))
22                         nospec_disable = 1;
23         } else {
24                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
25         }
26         return 0;
27 }
28 early_param("nobp", nobp_setup_early);
29
30 static int __init nospec_setup_early(char *str)
31 {
32         __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
33         return 0;
34 }
35 early_param("nospec", nospec_setup_early);
36
37 static int __init nospec_report(void)
38 {
39         if (test_facility(156))
40                 pr_info("Spectre V2 mitigation: etokens\n");
41         if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
42                 pr_info("Spectre V2 mitigation: execute trampolines\n");
43         if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
44                 pr_info("Spectre V2 mitigation: limited branch prediction\n");
45         return 0;
46 }
47 arch_initcall(nospec_report);
48
49 #ifdef CONFIG_EXPOLINE
50
51 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
52
53 static int __init nospectre_v2_setup_early(char *str)
54 {
55         nospec_disable = 1;
56         return 0;
57 }
58 early_param("nospectre_v2", nospectre_v2_setup_early);
59
60 void __init nospec_auto_detect(void)
61 {
62         if (test_facility(156) || cpu_mitigations_off()) {
63                 /*
64                  * The machine supports etokens.
65                  * Disable expolines and disable nobp.
66                  */
67                 if (IS_ENABLED(CC_USING_EXPOLINE))
68                         nospec_disable = 1;
69                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
70         } else if (IS_ENABLED(CC_USING_EXPOLINE)) {
71                 /*
72                  * The kernel has been compiled with expolines.
73                  * Keep expolines enabled and disable nobp.
74                  */
75                 nospec_disable = 0;
76                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
77         }
78         /*
79          * If the kernel has not been compiled with expolines the
80          * nobp setting decides what is done, this depends on the
81          * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
82          */
83 }
84
85 static int __init spectre_v2_setup_early(char *str)
86 {
87         if (str && !strncmp(str, "on", 2)) {
88                 nospec_disable = 0;
89                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
90         }
91         if (str && !strncmp(str, "off", 3))
92                 nospec_disable = 1;
93         if (str && !strncmp(str, "auto", 4))
94                 nospec_auto_detect();
95         return 0;
96 }
97 early_param("spectre_v2", spectre_v2_setup_early);
98
99 static void __init_or_module __nospec_revert(s32 *start, s32 *end)
100 {
101         enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
102         u8 *instr, *thunk, *br;
103         u8 insnbuf[6];
104         s32 *epo;
105
106         /* Second part of the instruction replace is always a nop */
107         for (epo = start; epo < end; epo++) {
108                 instr = (u8 *) epo + *epo;
109                 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
110                         type = BRCL_EXPOLINE;   /* brcl instruction */
111                 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
112                         type = BRASL_EXPOLINE;  /* brasl instruction */
113                 else
114                         continue;
115                 thunk = instr + (*(int *)(instr + 2)) * 2;
116                 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
117                         /* exrl %r0,<target-br> */
118                         br = thunk + (*(int *)(thunk + 2)) * 2;
119                 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
120                          thunk[6] == 0x44 && thunk[7] == 0x00 &&
121                          (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
122                          (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
123                         /* larl %rx,<target br> + ex %r0,0(%rx) */
124                         br = thunk + (*(int *)(thunk + 2)) * 2;
125                 else
126                         continue;
127                 /* Check for unconditional branch 0x07f? or 0x47f???? */
128                 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
129                         continue;
130
131                 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
132                 switch (type) {
133                 case BRCL_EXPOLINE:
134                         insnbuf[0] = br[0];
135                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
136                         if (br[0] == 0x47) {
137                                 /* brcl to b, replace with bc + nopr */
138                                 insnbuf[2] = br[2];
139                                 insnbuf[3] = br[3];
140                         } else {
141                                 /* brcl to br, replace with bcr + nop */
142                         }
143                         break;
144                 case BRASL_EXPOLINE:
145                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
146                         if (br[0] == 0x47) {
147                                 /* brasl to b, replace with bas + nopr */
148                                 insnbuf[0] = 0x4d;
149                                 insnbuf[2] = br[2];
150                                 insnbuf[3] = br[3];
151                         } else {
152                                 /* brasl to br, replace with basr + nop */
153                                 insnbuf[0] = 0x0d;
154                         }
155                         break;
156                 }
157
158                 s390_kernel_write(instr, insnbuf, 6);
159         }
160 }
161
162 void __init_or_module nospec_revert(s32 *start, s32 *end)
163 {
164         if (nospec_disable)
165                 __nospec_revert(start, end);
166 }
167
168 extern s32 __nospec_call_start[], __nospec_call_end[];
169 extern s32 __nospec_return_start[], __nospec_return_end[];
170 void __init nospec_init_branches(void)
171 {
172         nospec_revert(__nospec_call_start, __nospec_call_end);
173         nospec_revert(__nospec_return_start, __nospec_return_end);
174 }
175
176 #endif /* CONFIG_EXPOLINE */