1 // SPDX-License-Identifier: GPL-2.0 2 #include <linux/module.h> 3 #include <asm/nospec-branch.h> 4 5 int nospec_call_disable = IS_ENABLED(CONFIG_EXPOLINE_OFF); 6 int nospec_return_disable = !IS_ENABLED(CONFIG_EXPOLINE_FULL); 7 8 static int __init nospectre_v2_setup_early(char *str) 9 { 10 nospec_call_disable = 1; 11 nospec_return_disable = 1; 12 return 0; 13 } 14 early_param("nospectre_v2", nospectre_v2_setup_early); 15 16 static int __init spectre_v2_setup_early(char *str) 17 { 18 if (str && !strncmp(str, "on", 2)) { 19 nospec_call_disable = 0; 20 nospec_return_disable = 0; 21 } 22 if (str && !strncmp(str, "off", 3)) { 23 nospec_call_disable = 1; 24 nospec_return_disable = 1; 25 } 26 if (str && !strncmp(str, "auto", 4)) { 27 nospec_call_disable = 0; 28 nospec_return_disable = 1; 29 } 30 return 0; 31 } 32 early_param("spectre_v2", spectre_v2_setup_early); 33 34 static void __init_or_module __nospec_revert(s32 *start, s32 *end) 35 { 36 enum { BRCL_EXPOLINE, BRASL_EXPOLINE } type; 37 u8 *instr, *thunk, *br; 38 u8 insnbuf[6]; 39 s32 *epo; 40 41 /* Second part of the instruction replace is always a nop */ 42 memcpy(insnbuf + 2, (char[]) { 0x47, 0x00, 0x00, 0x00 }, 4); 43 for (epo = start; epo < end; epo++) { 44 instr = (u8 *) epo + *epo; 45 if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x04) 46 type = BRCL_EXPOLINE; /* brcl instruction */ 47 else if (instr[0] == 0xc0 && (instr[1] & 0x0f) == 0x05) 48 type = BRASL_EXPOLINE; /* brasl instruction */ 49 else 50 continue; 51 thunk = instr + (*(int *)(instr + 2)) * 2; 52 if (thunk[0] == 0xc6 && thunk[1] == 0x00) 53 /* exrl %r0,<target-br> */ 54 br = thunk + (*(int *)(thunk + 2)) * 2; 55 else if (thunk[0] == 0xc0 && (thunk[1] & 0x0f) == 0x00 && 56 thunk[6] == 0x44 && thunk[7] == 0x00 && 57 (thunk[8] & 0x0f) == 0x00 && thunk[9] == 0x00 && 58 (thunk[1] & 0xf0) == (thunk[8] & 0xf0)) 59 /* larl %rx,<target br> + ex %r0,0(%rx) */ 60 br = thunk + (*(int *)(thunk + 2)) * 2; 61 else 62 continue; 63 if (br[0] != 0x07 || (br[1] & 0xf0) != 0xf0) 64 continue; 65 switch (type) { 66 case BRCL_EXPOLINE: 67 /* brcl to thunk, replace with br + nop */ 68 insnbuf[0] = br[0]; 69 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); 70 break; 71 case BRASL_EXPOLINE: 72 /* brasl to thunk, replace with basr + nop */ 73 insnbuf[0] = 0x0d; 74 insnbuf[1] = (instr[1] & 0xf0) | (br[1] & 0x0f); 75 break; 76 } 77 78 s390_kernel_write(instr, insnbuf, 6); 79 } 80 } 81 82 void __init_or_module nospec_call_revert(s32 *start, s32 *end) 83 { 84 if (nospec_call_disable) 85 __nospec_revert(start, end); 86 } 87 88 void __init_or_module nospec_return_revert(s32 *start, s32 *end) 89 { 90 if (nospec_return_disable) 91 __nospec_revert(start, end); 92 } 93 94 extern s32 __nospec_call_start[], __nospec_call_end[]; 95 extern s32 __nospec_return_start[], __nospec_return_end[]; 96 void __init nospec_init_branches(void) 97 { 98 nospec_call_revert(__nospec_call_start, __nospec_call_end); 99 nospec_return_revert(__nospec_return_start, __nospec_return_end); 100 } 101