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 static void bug_at(const void *ip, int line) 20 { 21 /* 22 * The location is not an op that we were expecting. 23 * Something went wrong. Crash the box, as something could be 24 * corrupting the kernel. 25 */ 26 pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, line); 27 BUG(); 28 } 29 30 static const void * 31 __jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init) 32 { 33 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 34 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 35 const void *expect, *code; 36 const void *addr, *dest; 37 int line; 38 39 addr = (void *)jump_entry_code(entry); 40 dest = (void *)jump_entry_target(entry); 41 42 code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest); 43 44 if (init) { 45 expect = default_nop; line = __LINE__; 46 } else if (type == JUMP_LABEL_JMP) { 47 expect = ideal_nop; line = __LINE__; 48 } else { 49 expect = code; line = __LINE__; 50 } 51 52 if (memcmp(addr, expect, JUMP_LABEL_NOP_SIZE)) 53 bug_at(addr, line); 54 55 if (type == JUMP_LABEL_NOP) 56 code = ideal_nop; 57 58 return code; 59 } 60 61 static inline void __jump_label_transform(struct jump_entry *entry, 62 enum jump_label_type type, 63 int init) 64 { 65 const void *opcode = __jump_label_set_jump_code(entry, type, init); 66 67 /* 68 * As long as only a single processor is running and the code is still 69 * not marked as RO, text_poke_early() can be used; Checking that 70 * system_state is SYSTEM_BOOTING guarantees it. It will be set to 71 * SYSTEM_SCHEDULING before other cores are awaken and before the 72 * code is write-protected. 73 * 74 * At the time the change is being done, just ignore whether we 75 * are doing nop -> jump or jump -> nop transition, and assume 76 * always nop being the 'currently valid' instruction 77 */ 78 if (init || system_state == SYSTEM_BOOTING) { 79 text_poke_early((void *)jump_entry_code(entry), opcode, 80 JUMP_LABEL_NOP_SIZE); 81 return; 82 } 83 84 text_poke_bp((void *)jump_entry_code(entry), opcode, JUMP_LABEL_NOP_SIZE, NULL); 85 } 86 87 static void __ref jump_label_transform(struct jump_entry *entry, 88 enum jump_label_type type, 89 int init) 90 { 91 mutex_lock(&text_mutex); 92 __jump_label_transform(entry, type, init); 93 mutex_unlock(&text_mutex); 94 } 95 96 void arch_jump_label_transform(struct jump_entry *entry, 97 enum jump_label_type type) 98 { 99 jump_label_transform(entry, type, 0); 100 } 101 102 bool arch_jump_label_transform_queue(struct jump_entry *entry, 103 enum jump_label_type type) 104 { 105 const void *opcode; 106 107 if (system_state == SYSTEM_BOOTING) { 108 /* 109 * Fallback to the non-batching mode. 110 */ 111 arch_jump_label_transform(entry, type); 112 return true; 113 } 114 115 mutex_lock(&text_mutex); 116 opcode = __jump_label_set_jump_code(entry, type, 0); 117 text_poke_queue((void *)jump_entry_code(entry), 118 opcode, JUMP_LABEL_NOP_SIZE, NULL); 119 mutex_unlock(&text_mutex); 120 return true; 121 } 122 123 void arch_jump_label_transform_apply(void) 124 { 125 mutex_lock(&text_mutex); 126 text_poke_finish(); 127 mutex_unlock(&text_mutex); 128 } 129 130 static enum { 131 JL_STATE_START, 132 JL_STATE_NO_UPDATE, 133 JL_STATE_UPDATE, 134 } jlstate __initdata_or_module = JL_STATE_START; 135 136 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 137 enum jump_label_type type) 138 { 139 /* 140 * This function is called at boot up and when modules are 141 * first loaded. Check if the default nop, the one that is 142 * inserted at compile time, is the ideal nop. If it is, then 143 * we do not need to update the nop, and we can leave it as is. 144 * If it is not, then we need to update the nop to the ideal nop. 145 */ 146 if (jlstate == JL_STATE_START) { 147 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 148 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 149 150 if (memcmp(ideal_nop, default_nop, 5) != 0) 151 jlstate = JL_STATE_UPDATE; 152 else 153 jlstate = JL_STATE_NO_UPDATE; 154 } 155 if (jlstate == JL_STATE_UPDATE) 156 jump_label_transform(entry, type, 1); 157 } 158