1 // SPDX-License-Identifier: GPL-2.0
2 #include <linux/module.h>
3 #include <linux/device.h>
4 #include <asm/nospec-branch.h>
6 static int __init nobp_setup_early(char *str)
11 rc = kstrtobool(str, &enabled);
14 if (enabled && test_facility(82)) {
16 * The user explicitely requested nobp=1, enable it and
17 * disable the expoline support.
19 __set_facility(82, S390_lowcore.alt_stfle_fac_list);
20 if (IS_ENABLED(CONFIG_EXPOLINE))
23 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
27 early_param("nobp", nobp_setup_early);
29 static int __init nospec_setup_early(char *str)
31 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
34 early_param("nospec", nospec_setup_early);
36 static int __init nospec_report(void)
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");
46 arch_initcall(nospec_report);
48 #ifdef CONFIG_EXPOLINE
50 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF);
52 static int __init nospectre_v2_setup_early(char *str)
57 early_param("nospectre_v2", nospectre_v2_setup_early);
59 void __init nospec_auto_detect(void)
61 if (test_facility(156)) {
63 * The machine supports etokens.
64 * Disable expolines and disable nobp.
66 if (IS_ENABLED(CC_USING_EXPOLINE))
68 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
69 } else if (IS_ENABLED(CC_USING_EXPOLINE)) {
71 * The kernel has been compiled with expolines.
72 * Keep expolines enabled and disable nobp.
75 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
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.
84 static int __init spectre_v2_setup_early(char *str)
86 if (str && !strncmp(str, "on", 2)) {
88 __clear_facility(82, S390_lowcore.alt_stfle_fac_list);
90 if (str && !strncmp(str, "off", 3))
92 if (str && !strncmp(str, "auto", 4))
96 early_param("spectre_v2", spectre_v2_setup_early);
98 static void __init_or_module __nospec_revert(s32 *start, s32 *end)
100 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type;
101 u8 *instr, *thunk, *br;
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 */
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;
126 /* Check for unconditional branch 0x07f? or 0x47f???? */
127 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0)
130 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4);
134 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
136 /* brcl to b, replace with bc + nopr */
140 /* brcl to br, replace with bcr + nop */
144 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f);
146 /* brasl to b, replace with bas + nopr */
151 /* brasl to br, replace with basr + nop */
157 s390_kernel_write(instr, insnbuf, 6);
161 void __init_or_module nospec_revert(s32 *start, s32 *end)
164 __nospec_revert(start, end);
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)
171 nospec_revert(__nospec_call_start, __nospec_call_end);
172 nospec_revert(__nospec_return_start, __nospec_return_end);
175 #endif /* CONFIG_EXPOLINE */