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 void *(*poker)(void *, const void *, size_t), 41 int init) 42 { 43 union jump_code_union jmp; 44 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 45 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 46 const void *expect, *code; 47 int line; 48 49 jmp.jump = 0xe9; 50 jmp.offset = jump_entry_target(entry) - 51 (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); 52 53 if (early_boot_irqs_disabled) 54 poker = text_poke_early; 55 56 if (type == JUMP_LABEL_JMP) { 57 if (init) { 58 expect = default_nop; line = __LINE__; 59 } else { 60 expect = ideal_nop; line = __LINE__; 61 } 62 63 code = &jmp.code; 64 } else { 65 if (init) { 66 expect = default_nop; line = __LINE__; 67 } else { 68 expect = &jmp.code; line = __LINE__; 69 } 70 71 code = ideal_nop; 72 } 73 74 if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE)) 75 bug_at((void *)jump_entry_code(entry), line); 76 77 /* 78 * Make text_poke_bp() a default fallback poker. 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 */ 85 if (poker) { 86 (*poker)((void *)jump_entry_code(entry), code, 87 JUMP_LABEL_NOP_SIZE); 88 return; 89 } 90 91 text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE, 92 (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); 93 } 94 95 void arch_jump_label_transform(struct jump_entry *entry, 96 enum jump_label_type type) 97 { 98 mutex_lock(&text_mutex); 99 __jump_label_transform(entry, type, NULL, 0); 100 mutex_unlock(&text_mutex); 101 } 102 103 static enum { 104 JL_STATE_START, 105 JL_STATE_NO_UPDATE, 106 JL_STATE_UPDATE, 107 } jlstate __initdata_or_module = JL_STATE_START; 108 109 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 110 enum jump_label_type type) 111 { 112 /* 113 * This function is called at boot up and when modules are 114 * first loaded. Check if the default nop, the one that is 115 * inserted at compile time, is the ideal nop. If it is, then 116 * we do not need to update the nop, and we can leave it as is. 117 * If it is not, then we need to update the nop to the ideal nop. 118 */ 119 if (jlstate == JL_STATE_START) { 120 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 121 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 122 123 if (memcmp(ideal_nop, default_nop, 5) != 0) 124 jlstate = JL_STATE_UPDATE; 125 else 126 jlstate = JL_STATE_NO_UPDATE; 127 } 128 if (jlstate == JL_STATE_UPDATE) 129 __jump_label_transform(entry, type, text_poke_early, 1); 130 } 131