bdddaae9655984dfbf59ccee386c7bb3608cb183
[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 <asm/nospec-branch.h>
5
6 static 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 }
27 early_param("nobp", nobp_setup_early);
28
29 static int __init nospec_setup_early(char *str)
30 {
31         __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
32         return 0;
33 }
34 early_param("nospec", nospec_setup_early);
35
36 static int __init nospec_report(void)
37 {
38         if (test_facility(156))
39                 pr_info("Spectre V2 mitigation: etokens\n");
40         if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
41                 pr_info("Spectre V2 mitigation: execute trampolines\n");
42         if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
43                 pr_info("Spectre V2 mitigation: limited branch prediction\n");
44         return 0;
45 }
46 arch_initcall(nospec_report);
47
48 #ifdef CONFIG_EXPOLINE
49
50 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
51
52 static int __init nospectre_v2_setup_early(char *str)
53 {
54         nospec_disable = 1;
55         return 0;
56 }
57 early_param("nospectre_v2", nospectre_v2_setup_early);
58
59 void __init nospec_auto_detect(void)
60 {
61         if (test_facility(156)) {
62                 /*
63                  * The machine supports etokens.
64                  * Disable expolines and disable nobp.
65                  */
66                 if (IS_ENABLED(CC_USING_EXPOLINE))
67                         nospec_disable = 1;
68                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
69         } else if (IS_ENABLED(CC_USING_EXPOLINE)) {
70                 /*
71                  * The kernel has been compiled with expolines.
72                  * Keep expolines enabled and disable nobp.
73                  */
74                 nospec_disable = 0;
75                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
76         }
77         /*
78          * If the kernel has not been compiled with expolines the
79          * nobp setting decides what is done, this depends on the
80          * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
81          */
82 }
83
84 static int __init spectre_v2_setup_early(char *str)
85 {
86         if (str && !strncmp(str, "on", 2)) {
87                 nospec_disable = 0;
88                 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
89         }
90         if (str && !strncmp(str, "off", 3))
91                 nospec_disable = 1;
92         if (str && !strncmp(str, "auto", 4))
93                 nospec_auto_detect();
94         return 0;
95 }
96 early_param("spectre_v2", spectre_v2_setup_early);
97
98 static void __init_or_module __nospec_revert(s32 *start, s32 *end)
99 {
100         enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
101         u8 *instr, *thunk, *br;
102         u8 insnbuf[6];
103         s32 *epo;
104
105         /* Second part of the instruction replace is always a nop */
106         for (epo = start; epo < end; epo++) {
107                 instr = (u8 *) epo + *epo;
108                 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
109                         type = BRCL_EXPOLINE;   /* brcl instruction */
110                 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
111                         type = BRASL_EXPOLINE;  /* brasl instruction */
112                 else
113                         continue;
114                 thunk = instr + (*(int *)(instr + 2)) * 2;
115                 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
116                         /* exrl %r0,<target-br> */
117                         br = thunk + (*(int *)(thunk + 2)) * 2;
118                 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
119                          thunk[6] == 0x44 && thunk[7] == 0x00 &&
120                          (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
121                          (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
122                         /* larl %rx,<target br> + ex %r0,0(%rx) */
123                         br = thunk + (*(int *)(thunk + 2)) * 2;
124                 else
125                         continue;
126                 /* Check for unconditional branch 0x07f? or 0x47f???? */
127                 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
128                         continue;
129
130                 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
131                 switch (type) {
132                 case BRCL_EXPOLINE:
133                         insnbuf[0] = br[0];
134                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
135                         if (br[0] == 0x47) {
136                                 /* brcl to b, replace with bc + nopr */
137                                 insnbuf[2] = br[2];
138                                 insnbuf[3] = br[3];
139                         } else {
140                                 /* brcl to br, replace with bcr + nop */
141                         }
142                         break;
143                 case BRASL_EXPOLINE:
144                         insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
145                         if (br[0] == 0x47) {
146                                 /* brasl to b, replace with bas + nopr */
147                                 insnbuf[0] = 0x4d;
148                                 insnbuf[2] = br[2];
149                                 insnbuf[3] = br[3];
150                         } else {
151                                 /* brasl to br, replace with basr + nop */
152                                 insnbuf[0] = 0x0d;
153                         }
154                         break;
155                 }
156
157                 s390_kernel_write(instr, insnbuf, 6);
158         }
159 }
160
161 void __init_or_module nospec_revert(s32 *start, s32 *end)
162 {
163         if (nospec_disable)
164                 __nospec_revert(start, end);
165 }
166
167 extern s32 __nospec_call_start[], __nospec_call_end[];
168 extern s32 __nospec_return_start[], __nospec_return_end[];
169 void __init nospec_init_branches(void)
170 {
171         nospec_revert(__nospec_call_start, __nospec_call_end);
172         nospec_revert(__nospec_return_start, __nospec_return_end);
173 }
174
175 #endif /* CONFIG_EXPOLINE */