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 #include <asm/insn.h> 19 20 int arch_jump_entry_size(struct jump_entry *entry) 21 { 22 struct insn insn = {}; 23 24 insn_decode_kernel(&insn, (void *)jump_entry_code(entry)); 25 BUG_ON(insn.length != 2 && insn.length != 5); 26 27 return insn.length; 28 } 29 30 struct jump_label_patch { 31 const void *code; 32 int size; 33 }; 34 35 static struct jump_label_patch 36 __jump_label_patch(struct jump_entry *entry, enum jump_label_type type) 37 { 38 const void *expect, *code, *nop; 39 const void *addr, *dest; 40 int size; 41 42 addr = (void *)jump_entry_code(entry); 43 dest = (void *)jump_entry_target(entry); 44 45 size = arch_jump_entry_size(entry); 46 switch (size) { 47 case JMP8_INSN_SIZE: 48 code = text_gen_insn(JMP8_INSN_OPCODE, addr, dest); 49 nop = x86_nops[size]; 50 break; 51 52 case JMP32_INSN_SIZE: 53 code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest); 54 nop = x86_nops[size]; 55 break; 56 57 default: BUG(); 58 } 59 60 if (type == JUMP_LABEL_JMP) 61 expect = nop; 62 else 63 expect = code; 64 65 if (memcmp(addr, expect, size)) { 66 /* 67 * The location is not an op that we were expecting. 68 * Something went wrong. Crash the box, as something could be 69 * corrupting the kernel. 70 */ 71 pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) size:%d type:%d\n", 72 addr, addr, addr, expect, size, type); 73 BUG(); 74 } 75 76 if (type == JUMP_LABEL_NOP) 77 code = nop; 78 79 return (struct jump_label_patch){.code = code, .size = size}; 80 } 81 82 static inline void __jump_label_transform(struct jump_entry *entry, 83 enum jump_label_type type, 84 int init) 85 { 86 const struct jump_label_patch jlp = __jump_label_patch(entry, type); 87 88 /* 89 * As long as only a single processor is running and the code is still 90 * not marked as RO, text_poke_early() can be used; Checking that 91 * system_state is SYSTEM_BOOTING guarantees it. It will be set to 92 * SYSTEM_SCHEDULING before other cores are awaken and before the 93 * code is write-protected. 94 * 95 * At the time the change is being done, just ignore whether we 96 * are doing nop -> jump or jump -> nop transition, and assume 97 * always nop being the 'currently valid' instruction 98 */ 99 if (init || system_state == SYSTEM_BOOTING) { 100 text_poke_early((void *)jump_entry_code(entry), jlp.code, jlp.size); 101 return; 102 } 103 104 text_poke_bp((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL); 105 } 106 107 static void __ref jump_label_transform(struct jump_entry *entry, 108 enum jump_label_type type, 109 int init) 110 { 111 mutex_lock(&text_mutex); 112 __jump_label_transform(entry, type, init); 113 mutex_unlock(&text_mutex); 114 } 115 116 void arch_jump_label_transform(struct jump_entry *entry, 117 enum jump_label_type type) 118 { 119 jump_label_transform(entry, type, 0); 120 } 121 122 bool arch_jump_label_transform_queue(struct jump_entry *entry, 123 enum jump_label_type type) 124 { 125 struct jump_label_patch jlp; 126 127 if (system_state == SYSTEM_BOOTING) { 128 /* 129 * Fallback to the non-batching mode. 130 */ 131 arch_jump_label_transform(entry, type); 132 return true; 133 } 134 135 mutex_lock(&text_mutex); 136 jlp = __jump_label_patch(entry, type); 137 text_poke_queue((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL); 138 mutex_unlock(&text_mutex); 139 return true; 140 } 141 142 void arch_jump_label_transform_apply(void) 143 { 144 mutex_lock(&text_mutex); 145 text_poke_finish(); 146 mutex_unlock(&text_mutex); 147 } 148 149 static enum { 150 JL_STATE_START, 151 JL_STATE_NO_UPDATE, 152 JL_STATE_UPDATE, 153 } jlstate __initdata_or_module = JL_STATE_START; 154 155 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 156 enum jump_label_type type) 157 { 158 if (jlstate == JL_STATE_UPDATE) 159 jump_label_transform(entry, type, 1); 160 } 161