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 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 explicitely 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 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 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 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 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 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 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 } 141 142 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[]; 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