1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/module.h>
3 #include <linux/device.h>
4 #include <asm/facility.h>
5 #include <asm/nospec-branch.h>
6
nobp_setup_early(char * str)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
nospec_setup_early(char * str)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
nospec_report(void)37 static int __init nospec_report(void)
38 {
39 if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable)
40 pr_info("Spectre V2 mitigation: execute trampolines.\n");
41 if (__test_facility(82, S390_lowcore.alt_stfle_fac_list))
42 pr_info("Spectre V2 mitigation: limited branch prediction.\n");
43 return 0;
44 }
45 arch_initcall(nospec_report);
46
47 #ifdef CONFIG_EXPOLINE
48
49 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
50
nospectre_v2_setup_early(char * str)51 static int __init nospectre_v2_setup_early(char *str)
52 {
53 nospec_disable = 1;
54 return 0;
55 }
56 early_param("nospectre_v2", nospectre_v2_setup_early);
57
nospec_auto_detect(void)58 void __init nospec_auto_detect(void)
59 {
60 if (IS_ENABLED(CC_USING_EXPOLINE)) {
61 /*
62 * The kernel has been compiled with expolines.
63 * Keep expolines enabled and disable nobp.
64 */
65 nospec_disable = 0;
66 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
67 }
68 /*
69 * If the kernel has not been compiled with expolines the
70 * nobp setting decides what is done, this depends on the
71 * CONFIG_KERNEL_NP option and the nobp/nospec parameters.
72 */
73 }
74
spectre_v2_setup_early(char * str)75 static int __init spectre_v2_setup_early(char *str)
76 {
77 if (str && !strncmp(str, "on", 2)) {
78 nospec_disable = 0;
79 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
80 }
81 if (str && !strncmp(str, "off", 3))
82 nospec_disable = 1;
83 if (str && !strncmp(str, "auto", 4))
84 nospec_auto_detect();
85 return 0;
86 }
87 early_param("spectre_v2", spectre_v2_setup_early);
88
__nospec_revert(s32 * start,s32 * end)89 static void __init_or_module __nospec_revert(s32 *start, s32 *end)
90 {
91 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
92 u8 *instr, *thunk, *br;
93 u8 insnbuf[6];
94 s32 *epo;
95
96 /* Second part of the instruction replace is always a nop */
97 for (epo = start; epo < end; epo++) {
98 instr = (u8 *) epo + *epo;
99 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04)
100 type = BRCL_EXPOLINE; /* brcl instruction */
101 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05)
102 type = BRASL_EXPOLINE; /* brasl instruction */
103 else
104 continue;
105 thunk = instr + (*(int *)(instr + 2)) * 2;
106 if (thunk[0] == 0xc6 && thunk[1] == 0x00)
107 /* exrl %r0,<target-br> */
108 br = thunk + (*(int *)(thunk + 2)) * 2;
109 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 &&
110 thunk[6] == 0x44 && thunk[7] == 0x00 &&
111 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 &&
112 (thunk[1] & 0xf0) == (thunk[8] & 0xf0))
113 /* larl %rx,<target br> + ex %r0,0(%rx) */
114 br = thunk + (*(int *)(thunk + 2)) * 2;
115 else
116 continue;
117 /* Check for unconditional branch 0x07f? or 0x47f???? */
118 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
119 continue;
120
121 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
122 switch (type) {
123 case BRCL_EXPOLINE:
124 insnbuf[0] = br[0];
125 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
126 if (br[0] == 0x47) {
127 /* brcl to b, replace with bc + nopr */
128 insnbuf[2] = br[2];
129 insnbuf[3] = br[3];
130 } else {
131 /* brcl to br, replace with bcr + nop */
132 }
133 break;
134 case BRASL_EXPOLINE:
135 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
136 if (br[0] == 0x47) {
137 /* brasl to b, replace with bas + nopr */
138 insnbuf[0] = 0x4d;
139 insnbuf[2] = br[2];
140 insnbuf[3] = br[3];
141 } else {
142 /* brasl to br, replace with basr + nop */
143 insnbuf[0] = 0x0d;
144 }
145 break;
146 }
147
148 s390_kernel_write(instr, insnbuf, 6);
149 }
150 }
151
nospec_revert(s32 * start,s32 * end)152 void __init_or_module nospec_revert(s32 *start, s32 *end)
153 {
154 if (nospec_disable)
155 __nospec_revert(start, end);
156 }
157
158 extern s32 __nospec_call_start[], __nospec_call_end[];
159 extern s32 __nospec_return_start[], __nospec_return_end[];
nospec_init_branches(void)160 void __init nospec_init_branches(void)
161 {
162 nospec_revert(__nospec_call_start, __nospec_call_end);
163 nospec_revert(__nospec_return_start, __nospec_return_end);
164 }
165
166 #endif /* CONFIG_EXPOLINE */
167