1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * jump label x86 support 4 * 5 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com> 6 * 7 */ 8 #include <linux/jump_label.h> 9 #include <linux/memory.h> 10 #include <linux/uaccess.h> 11 #include <linux/module.h> 12 #include <linux/list.h> 13 #include <linux/jhash.h> 14 #include <linux/cpu.h> 15 #include <asm/kprobes.h> 16 #include <asm/alternative.h> 17 #include <asm/text-patching.h> 18 19 #ifdef HAVE_JUMP_LABEL 20 21 union jump_code_union { 22 char code[JUMP_LABEL_NOP_SIZE]; 23 struct { 24 char jump; 25 int offset; 26 } __attribute__((packed)); 27 }; 28 29 static void bug_at(unsigned char *ip, int line) 30 { 31 /* 32 * The location is not an op that we were expecting. 33 * Something went wrong. Crash the box, as something could be 34 * corrupting the kernel. 35 */ 36 pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, line); 37 BUG(); 38 } 39 40 static void __jump_label_transform(struct jump_entry *entry, 41 enum jump_label_type type, 42 void *(*poker)(void *, const void *, size_t), 43 int init) 44 { 45 union jump_code_union code; 46 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 47 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 48 49 if (type == JUMP_LABEL_JMP) { 50 if (init) { 51 /* 52 * Jump label is enabled for the first time. 53 * So we expect a default_nop... 54 */ 55 if (unlikely(memcmp((void *)entry->code, default_nop, 5) 56 != 0)) 57 bug_at((void *)entry->code, __LINE__); 58 } else { 59 /* 60 * ...otherwise expect an ideal_nop. Otherwise 61 * something went horribly wrong. 62 */ 63 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) 64 != 0)) 65 bug_at((void *)entry->code, __LINE__); 66 } 67 68 code.jump = 0xe9; 69 code.offset = entry->target - 70 (entry->code + JUMP_LABEL_NOP_SIZE); 71 } else { 72 /* 73 * We are disabling this jump label. If it is not what 74 * we think it is, then something must have gone wrong. 75 * If this is the first initialization call, then we 76 * are converting the default nop to the ideal nop. 77 */ 78 if (init) { 79 if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) 80 bug_at((void *)entry->code, __LINE__); 81 } else { 82 code.jump = 0xe9; 83 code.offset = entry->target - 84 (entry->code + JUMP_LABEL_NOP_SIZE); 85 if (unlikely(memcmp((void *)entry->code, &code, 5) != 0)) 86 bug_at((void *)entry->code, __LINE__); 87 } 88 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); 89 } 90 91 /* 92 * Make text_poke_bp() a default fallback poker. 93 * 94 * At the time the change is being done, just ignore whether we 95 * are doing nop -> jump or jump -> nop transition, and assume 96 * always nop being the 'currently valid' instruction 97 * 98 */ 99 if (poker) 100 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); 101 else 102 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE, 103 (void *)entry->code + JUMP_LABEL_NOP_SIZE); 104 } 105 106 void arch_jump_label_transform(struct jump_entry *entry, 107 enum jump_label_type type) 108 { 109 mutex_lock(&text_mutex); 110 __jump_label_transform(entry, type, NULL, 0); 111 mutex_unlock(&text_mutex); 112 } 113 114 static enum { 115 JL_STATE_START, 116 JL_STATE_NO_UPDATE, 117 JL_STATE_UPDATE, 118 } jlstate __initdata_or_module = JL_STATE_START; 119 120 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 121 enum jump_label_type type) 122 { 123 /* 124 * This function is called at boot up and when modules are 125 * first loaded. Check if the default nop, the one that is 126 * inserted at compile time, is the ideal nop. If it is, then 127 * we do not need to update the nop, and we can leave it as is. 128 * If it is not, then we need to update the nop to the ideal nop. 129 */ 130 if (jlstate == JL_STATE_START) { 131 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 132 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 133 134 if (memcmp(ideal_nop, default_nop, 5) != 0) 135 jlstate = JL_STATE_UPDATE; 136 else 137 jlstate = JL_STATE_NO_UPDATE; 138 } 139 if (jlstate == JL_STATE_UPDATE) 140 __jump_label_transform(entry, type, text_poke_early, 1); 141 } 142 143 #endif 144