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(s: str, res: &enabled); |
13 | if (rc) |
14 | return rc; |
15 | if (enabled && test_facility(82)) { |
16 | /* |
17 | * The user explicitly requested nobp=1, enable it and |
18 | * disable the expoline support. |
19 | */ |
20 | __set_facility(82, alt_stfle_fac_list); |
21 | if (IS_ENABLED(CONFIG_EXPOLINE)) |
22 | nospec_disable = 1; |
23 | } else { |
24 | __clear_facility(82, 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, 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 (nospec_uses_trampoline()) |
42 | pr_info("Spectre V2 mitigation: execute trampolines\n" ); |
43 | if (__test_facility(82, 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_defined(CC_USING_EXPOLINE)) |
68 | nospec_disable = 1; |
69 | __clear_facility(82, alt_stfle_fac_list); |
70 | } else if (__is_defined(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, 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, 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 | static const u8 branch[] = { 0x47, 0x00, 0x07, 0x00 }; |
103 | u8 *instr, *thunk, *br; |
104 | u8 insnbuf[6]; |
105 | s32 *epo; |
106 | |
107 | /* Second part of the instruction replace is always a nop */ |
108 | memcpy(insnbuf + 2, branch, sizeof(branch)); |
109 | for (epo = start; epo < end; epo++) { |
110 | instr = (u8 *) epo + *epo; |
111 | if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04) |
112 | type = BRCL_EXPOLINE; /* brcl instruction */ |
113 | else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05) |
114 | type = BRASL_EXPOLINE; /* brasl instruction */ |
115 | else |
116 | continue; |
117 | thunk = instr + (*(int *)(instr + 2)) * 2; |
118 | if (thunk[0] == 0xc6 && thunk[1] == 0x00) |
119 | /* exrl %r0,<target-br> */ |
120 | br = thunk + (*(int *)(thunk + 2)) * 2; |
121 | else |
122 | continue; |
123 | if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0) |
124 | continue; |
125 | switch (type) { |
126 | case BRCL_EXPOLINE: |
127 | /* brcl to thunk, replace with br + nop */ |
128 | insnbuf[0] = br[0]; |
129 | insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); |
130 | break; |
131 | case BRASL_EXPOLINE: |
132 | /* brasl to thunk, replace with basr + nop */ |
133 | insnbuf[0] = 0x0d; |
134 | insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); |
135 | break; |
136 | } |
137 | |
138 | s390_kernel_write(instr, insnbuf, 6); |
139 | } |
140 | } |
141 | |
142 | void __init_or_module nospec_revert(s32 *start, s32 *end) |
143 | { |
144 | if (nospec_disable) |
145 | __nospec_revert(start, end); |
146 | } |
147 | |
148 | extern s32 __nospec_call_start[], __nospec_call_end[]; |
149 | extern s32 __nospec_return_start[], __nospec_return_end[]; |
150 | void __init nospec_init_branches(void) |
151 | { |
152 | nospec_revert(__nospec_call_start, __nospec_call_end); |
153 | nospec_revert(__nospec_return_start, __nospec_return_end); |
154 | } |
155 | |
156 | #endif /* CONFIG_EXPOLINE */ |
157 | |