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 __ref __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 (early_boot_irqs_disabled) 50 poker = text_poke_early; 51 52 if (type == JUMP_LABEL_JMP) { 53 if (init) { 54 /* 55 * Jump label is enabled for the first time. 56 * So we expect a default_nop... 57 */ 58 if (unlikely(memcmp((void *)entry->code, default_nop, 5) 59 != 0)) 60 bug_at((void *)entry->code, __LINE__); 61 } else { 62 /* 63 * ...otherwise expect an ideal_nop. Otherwise 64 * something went horribly wrong. 65 */ 66 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) 67 != 0)) 68 bug_at((void *)entry->code, __LINE__); 69 } 70 71 code.jump = 0xe9; 72 code.offset = entry->target - 73 (entry->code + JUMP_LABEL_NOP_SIZE); 74 } else { 75 /* 76 * We are disabling this jump label. If it is not what 77 * we think it is, then something must have gone wrong. 78 * If this is the first initialization call, then we 79 * are converting the default nop to the ideal nop. 80 */ 81 if (init) { 82 if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) 83 bug_at((void *)entry->code, __LINE__); 84 } else { 85 code.jump = 0xe9; 86 code.offset = entry->target - 87 (entry->code + JUMP_LABEL_NOP_SIZE); 88 if (unlikely(memcmp((void *)entry->code, &code, 5) != 0)) 89 bug_at((void *)entry->code, __LINE__); 90 } 91 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); 92 } 93 94 /* 95 * Make text_poke_bp() a default fallback poker. 96 * 97 * At the time the change is being done, just ignore whether we 98 * are doing nop -> jump or jump -> nop transition, and assume 99 * always nop being the 'currently valid' instruction 100 * 101 */ 102 if (poker) 103 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); 104 else 105 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE, 106 (void *)entry->code + JUMP_LABEL_NOP_SIZE); 107 } 108 109 void arch_jump_label_transform(struct jump_entry *entry, 110 enum jump_label_type type) 111 { 112 mutex_lock(&text_mutex); 113 __jump_label_transform(entry, type, NULL, 0); 114 mutex_unlock(&text_mutex); 115 } 116 117 static enum { 118 JL_STATE_START, 119 JL_STATE_NO_UPDATE, 120 JL_STATE_UPDATE, 121 } jlstate __initdata_or_module = JL_STATE_START; 122 123 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 124 enum jump_label_type type) 125 { 126 /* 127 * This function is called at boot up and when modules are 128 * first loaded. Check if the default nop, the one that is 129 * inserted at compile time, is the ideal nop. If it is, then 130 * we do not need to update the nop, and we can leave it as is. 131 * If it is not, then we need to update the nop to the ideal nop. 132 */ 133 if (jlstate == JL_STATE_START) { 134 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 135 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 136 137 if (memcmp(ideal_nop, default_nop, 5) != 0) 138 jlstate = JL_STATE_UPDATE; 139 else 140 jlstate = JL_STATE_NO_UPDATE; 141 } 142 if (jlstate == JL_STATE_UPDATE) 143 __jump_label_transform(entry, type, text_poke_early, 1); 144 } 145 146 #endif 147