1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/module.h> 3 #include <linux/device.h> 4 #include <asm/nospec-branch.h> 5 6 static int __init nobp_setup_early(char *str) 7 { 8 bool enabled; 9 int rc; 10 11 rc = kstrtobool(str, &enabled); 12 if (rc) 13 return rc; 14 if (enabled && test_facility(82)) { 15 /* 16 * The user explicitely requested nobp=1, enable it and 17 * disable the expoline support. 18 */ 19 __set_facility(82, S390_lowcore.alt_stfle_fac_list); 20 if (IS_ENABLED(CONFIG_EXPOLINE)) 21 nospec_disable = 1; 22 } else { 23 __clear_facility(82, S390_lowcore.alt_stfle_fac_list); 24 } 25 return 0; 26 } 27 early_param("nobp", nobp_setup_early); 28 29 static int __init nospec_setup_early(char *str) 30 { 31 __clear_facility(82, S390_lowcore.alt_stfle_fac_list); 32 return 0; 33 } 34 early_param("nospec", nospec_setup_early); 35 36 static int __init nospec_report(void) 37 { 38 if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable) 39 pr_info("Spectre V2 mitigation: execute trampolines.\n"); 40 if (__test_facility(82, S390_lowcore.alt_stfle_fac_list)) 41 pr_info("Spectre V2 mitigation: limited branch prediction.\n"); 42 return 0; 43 } 44 arch_initcall(nospec_report); 45 46 #ifdef CONFIG_SYSFS 47 ssize_t cpu_show_spectre_v1(struct device *dev, 48 struct device_attribute *attr, char *buf) 49 { 50 return sprintf(buf, "Mitigation: __user pointer sanitization\n"); 51 } 52 53 ssize_t cpu_show_spectre_v2(struct device *dev, 54 struct device_attribute *attr, char *buf) 55 { 56 if (IS_ENABLED(CC_USING_EXPOLINE) && !nospec_disable) 57 return sprintf(buf, "Mitigation: execute trampolines\n"); 58 if (__test_facility(82, S390_lowcore.alt_stfle_fac_list)) 59 return sprintf(buf, "Mitigation: limited branch prediction.\n"); 60 return sprintf(buf, "Vulnerable\n"); 61 } 62 #endif 63 64 #ifdef CONFIG_EXPOLINE 65 66 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF); 67 68 static int __init nospectre_v2_setup_early(char *str) 69 { 70 nospec_disable = 1; 71 return 0; 72 } 73 early_param("nospectre_v2", nospectre_v2_setup_early); 74 75 static int __init spectre_v2_auto_early(void) 76 { 77 if (IS_ENABLED(CC_USING_EXPOLINE)) { 78 /* 79 * The kernel has been compiled with expolines. 80 * Keep expolines enabled and disable nobp. 81 */ 82 nospec_disable = 0; 83 __clear_facility(82, S390_lowcore.alt_stfle_fac_list); 84 } 85 /* 86 * If the kernel has not been compiled with expolines the 87 * nobp setting decides what is done, this depends on the 88 * CONFIG_KERNEL_NP option and the nobp/nospec parameters. 89 */ 90 return 0; 91 } 92 #ifdef CONFIG_EXPOLINE_AUTO 93 early_initcall(spectre_v2_auto_early); 94 #endif 95 96 static int __init spectre_v2_setup_early(char *str) 97 { 98 if (str && !strncmp(str, "on", 2)) { 99 nospec_disable = 0; 100 __clear_facility(82, S390_lowcore.alt_stfle_fac_list); 101 } 102 if (str && !strncmp(str, "off", 3)) 103 nospec_disable = 1; 104 if (str && !strncmp(str, "auto", 4)) 105 spectre_v2_auto_early(); 106 return 0; 107 } 108 early_param("spectre_v2", spectre_v2_setup_early); 109 110 static void __init_or_module __nospec_revert(s32 *start, s32 *end) 111 { 112 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type; 113 u8 *instr, *thunk, *br; 114 u8 insnbuf[6]; 115 s32 *epo; 116 117 /* Second part of the instruction replace is always a nop */ 118 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4); 119 for (epo = start; epo < end; epo++) { 120 instr = (u8 *) epo + *epo; 121 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04) 122 type = BRCL_EXPOLINE; /* brcl instruction */ 123 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05) 124 type = BRASL_EXPOLINE; /* brasl instruction */ 125 else 126 continue; 127 thunk = instr + (*(int *)(instr + 2)) * 2; 128 if (thunk[0] == 0xc6 && thunk[1] == 0x00) 129 /* exrl %r0,<target-br> */ 130 br = thunk + (*(int *)(thunk + 2)) * 2; 131 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 && 132 thunk[6] == 0x44 && thunk[7] == 0x00 && 133 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 && 134 (thunk[1] & 0xf0) == (thunk[8] & 0xf0)) 135 /* larl %rx,<target br> + ex %r0,0(%rx) */ 136 br = thunk + (*(int *)(thunk + 2)) * 2; 137 else 138 continue; 139 if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0) 140 continue; 141 switch (type) { 142 case BRCL_EXPOLINE: 143 /* brcl to thunk, replace with br + nop */ 144 insnbuf[0] = br[0]; 145 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); 146 break; 147 case BRASL_EXPOLINE: 148 /* brasl to thunk, replace with basr + nop */ 149 insnbuf[0] = 0x0d; 150 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); 151 break; 152 } 153 154 s390_kernel_write(instr, insnbuf, 6); 155 } 156 } 157 158 void __init_or_module nospec_revert(s32 *start, s32 *end) 159 { 160 if (nospec_disable) 161 __nospec_revert(start, end); 162 } 163 164 extern s32 __nospec_call_start[], __nospec_call_end[]; 165 extern s32 __nospec_return_start[], __nospec_return_end[]; 166 void __init nospec_init_branches(void) 167 { 168 nospec_revert(__nospec_call_start, __nospec_call_end); 169 nospec_revert(__nospec_return_start, __nospec_return_end); 170 } 171 172 #endif /* CONFIG_EXPOLINE */ 173