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_EXPOLINE 47 48 int nospec_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF); 49 50 static int __init nospectre_v2_setup_early(char *str) 51 { 52 nospec_disable = 1; 53 return 0; 54 } 55 early_param("nospectre_v2", nospectre_v2_setup_early); 56 57 void __init nospec_auto_detect(void) 58 { 59 if (IS_ENABLED(CC_USING_EXPOLINE)) { 60 /* 61 * The kernel has been compiled with expolines. 62 * Keep expolines enabled and disable nobp. 63 */ 64 nospec_disable = 0; 65 __clear_facility(82, S390_lowcore.alt_stfle_fac_list); 66 } 67 /* 68 * If the kernel has not been compiled with expolines the 69 * nobp setting decides what is done, this depends on the 70 * CONFIG_KERNEL_NP option and the nobp/nospec parameters. 71 */ 72 } 73 74 static int __init spectre_v2_setup_early(char *str) 75 { 76 if (str && !strncmp(str, "on", 2)) { 77 nospec_disable = 0; 78 __clear_facility(82, S390_lowcore.alt_stfle_fac_list); 79 } 80 if (str && !strncmp(str, "off", 3)) 81 nospec_disable = 1; 82 if (str && !strncmp(str, "auto", 4)) 83 nospec_auto_detect(); 84 return 0; 85 } 86 early_param("spectre_v2", spectre_v2_setup_early); 87 88 static void __init_or_module __nospec_revert(s32 *start, s32 *end) 89 { 90 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type; 91 u8 *instr, *thunk, *br; 92 u8 insnbuf[6]; 93 s32 *epo; 94 95 /* Second part of the instruction replace is always a nop */ 96 for (epo = start; epo < end; epo++) { 97 instr = (u8 *) epo + *epo; 98 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04) 99 type = BRCL_EXPOLINE; /* brcl instruction */ 100 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05) 101 type = BRASL_EXPOLINE; /* brasl instruction */ 102 else 103 continue; 104 thunk = instr + (*(int *)(instr + 2)) * 2; 105 if (thunk[0] == 0xc6 && thunk[1] == 0x00) 106 /* exrl %r0,<target-br> */ 107 br = thunk + (*(int *)(thunk + 2)) * 2; 108 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 && 109 thunk[6] == 0x44 && thunk[7] == 0x00 && 110 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 && 111 (thunk[1] & 0xf0) == (thunk[8] & 0xf0)) 112 /* larl %rx,<target br> + ex %r0,0(%rx) */ 113 br = thunk + (*(int *)(thunk + 2)) * 2; 114 else 115 continue; 116 /* Check for unconditional branch 0x07f? or 0x47f???? */ 117 if ((br[0] & 0xbf) != 0x07 || (br[1] & 0xf0) != 0xf0) 118 continue; 119 120 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x07, 0x00 }, 4); 121 switch (type) { 122 case BRCL_EXPOLINE: 123 insnbuf[0] = br[0]; 124 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); 125 if (br[0] == 0x47) { 126 /* brcl to b, replace with bc + nopr */ 127 insnbuf[2] = br[2]; 128 insnbuf[3] = br[3]; 129 } else { 130 /* brcl to br, replace with bcr + nop */ 131 } 132 break; 133 case BRASL_EXPOLINE: 134 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); 135 if (br[0] == 0x47) { 136 /* brasl to b, replace with bas + nopr */ 137 insnbuf[0] = 0x4d; 138 insnbuf[2] = br[2]; 139 insnbuf[3] = br[3]; 140 } else { 141 /* brasl to br, replace with basr + nop */ 142 insnbuf[0] = 0x0d; 143 } 144 break; 145 } 146 147 s390_kernel_write(instr, insnbuf, 6); 148 } 149 } 150 151 void __init_or_module nospec_revert(s32 *start, s32 *end) 152 { 153 if (nospec_disable) 154 __nospec_revert(start, end); 155 } 156 157 extern s32 __nospec_call_start[], __nospec_call_end[]; 158 extern s32 __nospec_return_start[], __nospec_return_end[]; 159 void __init nospec_init_branches(void) 160 { 161 nospec_revert(__nospec_call_start, __nospec_call_end); 162 nospec_revert(__nospec_return_start, __nospec_return_end); 163 } 164 165 #endif /* CONFIG_EXPOLINE */ 166