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f19fbd5e MS |
1 | // SPDX-License-Identifier: GPL-2.0 |
2 | #include <linux/module.h> | |
3 | #include <asm/nospec-branch.h> | |
4 | ||
2cb370d6 ER |
5 | int nospec_call_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF); |
6 | int nospec_return_disable = !IS_ENABLED(CONFIG_EXPOLINE_FULL); | |
f19fbd5e MS |
7 | |
8 | static int __init nospectre_v2_setup_early(char *str) | |
9 | { | |
10 | nospec_call_disable = 1; | |
11 | nospec_return_disable = 1; | |
12 | return 0; | |
13 | } | |
14 | early_param("nospectre_v2", nospectre_v2_setup_early); | |
15 | ||
16 | static int __init spectre_v2_setup_early(char *str) | |
17 | { | |
18 | if (str && !strncmp(str, "on", 2)) { | |
19 | nospec_call_disable = 0; | |
20 | nospec_return_disable = 0; | |
21 | } | |
22 | if (str && !strncmp(str, "off", 3)) { | |
23 | nospec_call_disable = 1; | |
24 | nospec_return_disable = 1; | |
25 | } | |
26 | if (str && !strncmp(str, "auto", 4)) { | |
27 | nospec_call_disable = 0; | |
28 | nospec_return_disable = 1; | |
29 | } | |
30 | return 0; | |
31 | } | |
32 | early_param("spectre_v2", spectre_v2_setup_early); | |
33 | ||
34 | static void __init_or_module __nospec_revert(s32 *start, s32 *end) | |
35 | { | |
36 | enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type; | |
37 | u8 *instr, *thunk, *br; | |
38 | u8 insnbuf[6]; | |
39 | s32 *epo; | |
40 | ||
41 | /* Second part of the instruction replace is always a nop */ | |
42 | memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4); | |
43 | for (epo = start; epo < end; epo++) { | |
44 | instr = (u8 *) epo + *epo; | |
45 | if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04) | |
46 | type = BRCL_EXPOLINE; /* brcl instruction */ | |
47 | else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05) | |
48 | type = BRASL_EXPOLINE; /* brasl instruction */ | |
49 | else | |
50 | continue; | |
51 | thunk = instr + (*(int *)(instr + 2)) * 2; | |
52 | if (thunk[0] == 0xc6 && thunk[1] == 0x00) | |
53 | /* exrl %r0,<target-br> */ | |
54 | br = thunk + (*(int *)(thunk + 2)) * 2; | |
55 | else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 && | |
56 | thunk[6] == 0x44 && thunk[7] == 0x00 && | |
57 | (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 && | |
58 | (thunk[1] & 0xf0) == (thunk[8] & 0xf0)) | |
59 | /* larl %rx,<target br> + ex %r0,0(%rx) */ | |
60 | br = thunk + (*(int *)(thunk + 2)) * 2; | |
61 | else | |
62 | continue; | |
63 | if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0) | |
64 | continue; | |
65 | switch (type) { | |
66 | case BRCL_EXPOLINE: | |
67 | /* brcl to thunk, replace with br + nop */ | |
68 | insnbuf[0] = br[0]; | |
69 | insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); | |
70 | break; | |
71 | case BRASL_EXPOLINE: | |
72 | /* brasl to thunk, replace with basr + nop */ | |
73 | insnbuf[0] = 0x0d; | |
74 | insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); | |
75 | break; | |
76 | } | |
77 | ||
78 | s390_kernel_write(instr, insnbuf, 6); | |
79 | } | |
80 | } | |
81 | ||
82 | void __init_or_module nospec_call_revert(s32 *start, s32 *end) | |
83 | { | |
84 | if (nospec_call_disable) | |
85 | __nospec_revert(start, end); | |
86 | } | |
87 | ||
88 | void __init_or_module nospec_return_revert(s32 *start, s32 *end) | |
89 | { | |
90 | if (nospec_return_disable) | |
91 | __nospec_revert(start, end); | |
92 | } | |
93 | ||
94 | extern s32 __nospec_call_start[], __nospec_call_end[]; | |
95 | extern s32 __nospec_return_start[], __nospec_return_end[]; | |
96 | void __init nospec_init_branches(void) | |
97 | { | |
98 | nospec_call_revert(__nospec_call_start, __nospec_call_end); | |
99 | nospec_return_revert(__nospec_return_start, __nospec_return_end); | |
100 | } |