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 __always_inline void 83 __jump_label_transform(struct jump_entry *entry, 84 enum jump_label_type type, 85 int init) 86 { 87 const struct jump_label_patch jlp = __jump_label_patch(entry, type); 88 89 /* 90 * As long as only a single processor is running and the code is still 91 * not marked as RO, text_poke_early() can be used; Checking that 92 * system_state is SYSTEM_BOOTING guarantees it. It will be set to 93 * SYSTEM_SCHEDULING before other cores are awaken and before the 94 * code is write-protected. 95 * 96 * At the time the change is being done, just ignore whether we 97 * are doing nop -> jump or jump -> nop transition, and assume 98 * always nop being the 'currently valid' instruction 99 */ 100 if (init || system_state == SYSTEM_BOOTING) { 101 text_poke_early((void *)jump_entry_code(entry), jlp.code, jlp.size); 102 return; 103 } 104 105 text_poke_bp((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL); 106 } 107 108 static void __ref jump_label_transform(struct jump_entry *entry, 109 enum jump_label_type type, 110 int init) 111 { 112 mutex_lock(&text_mutex); 113 __jump_label_transform(entry, type, init); 114 mutex_unlock(&text_mutex); 115 } 116 117 void arch_jump_label_transform(struct jump_entry *entry, 118 enum jump_label_type type) 119 { 120 jump_label_transform(entry, type, 0); 121 } 122 123 bool arch_jump_label_transform_queue(struct jump_entry *entry, 124 enum jump_label_type type) 125 { 126 struct jump_label_patch jlp; 127 128 if (system_state == SYSTEM_BOOTING) { 129 /* 130 * Fallback to the non-batching mode. 131 */ 132 arch_jump_label_transform(entry, type); 133 return true; 134 } 135 136 mutex_lock(&text_mutex); 137 jlp = __jump_label_patch(entry, type); 138 text_poke_queue((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL); 139 mutex_unlock(&text_mutex); 140 return true; 141 } 142 143 void arch_jump_label_transform_apply(void) 144 { 145 mutex_lock(&text_mutex); 146 text_poke_finish(); 147 mutex_unlock(&text_mutex); 148 } 149 150 static enum { 151 JL_STATE_START, 152 JL_STATE_NO_UPDATE, 153 JL_STATE_UPDATE, 154 } jlstate __initdata_or_module = JL_STATE_START; 155 156 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 157 enum jump_label_type type) 158 { 159 if (jlstate == JL_STATE_UPDATE) 160 jump_label_transform(entry, type, 1); 161 } 162