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 union jump_code_union { 20 char code[JUMP_LABEL_NOP_SIZE]; 21 struct { 22 char jump; 23 int offset; 24 } __attribute__((packed)); 25 }; 26 27 static void bug_at(unsigned char *ip, int line) 28 { 29 /* 30 * The location is not an op that we were expecting. 31 * Something went wrong. Crash the box, as something could be 32 * corrupting the kernel. 33 */ 34 pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, line); 35 BUG(); 36 } 37 38 static void __ref __jump_label_transform(struct jump_entry *entry, 39 enum jump_label_type type, 40 int init) 41 { 42 union jump_code_union jmp; 43 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 44 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 45 const void *expect, *code; 46 int line; 47 48 jmp.jump = 0xe9; 49 jmp.offset = jump_entry_target(entry) - 50 (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); 51 52 if (type == JUMP_LABEL_JMP) { 53 if (init) { 54 expect = default_nop; line = __LINE__; 55 } else { 56 expect = ideal_nop; line = __LINE__; 57 } 58 59 code = &jmp.code; 60 } else { 61 if (init) { 62 expect = default_nop; line = __LINE__; 63 } else { 64 expect = &jmp.code; line = __LINE__; 65 } 66 67 code = ideal_nop; 68 } 69 70 if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE)) 71 bug_at((void *)jump_entry_code(entry), line); 72 73 /* 74 * As long as only a single processor is running and the code is still 75 * not marked as RO, text_poke_early() can be used; Checking that 76 * system_state is SYSTEM_BOOTING guarantees it. It will be set to 77 * SYSTEM_SCHEDULING before other cores are awaken and before the 78 * code is write-protected. 79 * 80 * At the time the change is being done, just ignore whether we 81 * are doing nop -> jump or jump -> nop transition, and assume 82 * always nop being the 'currently valid' instruction 83 */ 84 if (init || system_state == SYSTEM_BOOTING) { 85 text_poke_early((void *)jump_entry_code(entry), code, 86 JUMP_LABEL_NOP_SIZE); 87 return; 88 } 89 90 text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE, 91 (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); 92 } 93 94 void arch_jump_label_transform(struct jump_entry *entry, 95 enum jump_label_type type) 96 { 97 mutex_lock(&text_mutex); 98 __jump_label_transform(entry, type, 0); 99 mutex_unlock(&text_mutex); 100 } 101 102 static enum { 103 JL_STATE_START, 104 JL_STATE_NO_UPDATE, 105 JL_STATE_UPDATE, 106 } jlstate __initdata_or_module = JL_STATE_START; 107 108 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 109 enum jump_label_type type) 110 { 111 /* 112 * This function is called at boot up and when modules are 113 * first loaded. Check if the default nop, the one that is 114 * inserted at compile time, is the ideal nop. If it is, then 115 * we do not need to update the nop, and we can leave it as is. 116 * If it is not, then we need to update the nop to the ideal nop. 117 */ 118 if (jlstate == JL_STATE_START) { 119 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 120 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 121 122 if (memcmp(ideal_nop, default_nop, 5) != 0) 123 jlstate = JL_STATE_UPDATE; 124 else 125 jlstate = JL_STATE_NO_UPDATE; 126 } 127 if (jlstate == JL_STATE_UPDATE) 128 __jump_label_transform(entry, type, 1); 129 } 130