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
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 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
nospec_setup_early(char * str)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
nospec_report(void)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
nospectre_v2_setup_early(char * str)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
nospec_auto_detect(void)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
spectre_v2_setup_early(char * str)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
__nospec_revert(s32 * start,s32 * end)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
nospec_revert(s32 * start,s32 * end)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[];
nospec_init_branches(void)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
