1 /* 2 * jump label x86 support 3 * 4 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com> 5 * 6 */ 7 #include <linux/jump_label.h> 8 #include <linux/memory.h> 9 #include <linux/uaccess.h> 10 #include <linux/module.h> 11 #include <linux/list.h> 12 #include <linux/jhash.h> 13 #include <linux/cpu.h> 14 #include <asm/kprobes.h> 15 #include <asm/alternative.h> 16 17 #ifdef HAVE_JUMP_LABEL 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_warning("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n", 35 ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line); 36 BUG(); 37 } 38 39 static void __jump_label_transform(struct jump_entry *entry, 40 enum jump_label_type type, 41 void *(*poker)(void *, const void *, size_t), 42 int init) 43 { 44 union jump_code_union code; 45 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 46 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 47 48 if (type == JUMP_LABEL_JMP) { 49 if (init) { 50 /* 51 * Jump label is enabled for the first time. 52 * So we expect a default_nop... 53 */ 54 if (unlikely(memcmp((void *)entry->code, default_nop, 5) 55 != 0)) 56 bug_at((void *)entry->code, __LINE__); 57 } else { 58 /* 59 * ...otherwise expect an ideal_nop. Otherwise 60 * something went horribly wrong. 61 */ 62 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) 63 != 0)) 64 bug_at((void *)entry->code, __LINE__); 65 } 66 67 code.jump = 0xe9; 68 code.offset = entry->target - 69 (entry->code + JUMP_LABEL_NOP_SIZE); 70 } else { 71 /* 72 * We are disabling this jump label. If it is not what 73 * we think it is, then something must have gone wrong. 74 * If this is the first initialization call, then we 75 * are converting the default nop to the ideal nop. 76 */ 77 if (init) { 78 if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) 79 bug_at((void *)entry->code, __LINE__); 80 } else { 81 code.jump = 0xe9; 82 code.offset = entry->target - 83 (entry->code + JUMP_LABEL_NOP_SIZE); 84 if (unlikely(memcmp((void *)entry->code, &code, 5) != 0)) 85 bug_at((void *)entry->code, __LINE__); 86 } 87 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); 88 } 89 90 /* 91 * Make text_poke_bp() a default fallback poker. 92 * 93 * At the time the change is being done, just ignore whether we 94 * are doing nop -> jump or jump -> nop transition, and assume 95 * always nop being the 'currently valid' instruction 96 * 97 */ 98 if (poker) 99 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); 100 else 101 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE, 102 (void *)entry->code + JUMP_LABEL_NOP_SIZE); 103 } 104 105 void arch_jump_label_transform(struct jump_entry *entry, 106 enum jump_label_type type) 107 { 108 get_online_cpus(); 109 mutex_lock(&text_mutex); 110 __jump_label_transform(entry, type, NULL, 0); 111 mutex_unlock(&text_mutex); 112 put_online_cpus(); 113 } 114 115 static enum { 116 JL_STATE_START, 117 JL_STATE_NO_UPDATE, 118 JL_STATE_UPDATE, 119 } jlstate __initdata_or_module = JL_STATE_START; 120 121 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 122 enum jump_label_type type) 123 { 124 /* 125 * This function is called at boot up and when modules are 126 * first loaded. Check if the default nop, the one that is 127 * inserted at compile time, is the ideal nop. If it is, then 128 * we do not need to update the nop, and we can leave it as is. 129 * If it is not, then we need to update the nop to the ideal nop. 130 */ 131 if (jlstate == JL_STATE_START) { 132 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 133 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 134 135 if (memcmp(ideal_nop, default_nop, 5) != 0) 136 jlstate = JL_STATE_UPDATE; 137 else 138 jlstate = JL_STATE_NO_UPDATE; 139 } 140 if (jlstate == JL_STATE_UPDATE) 141 __jump_label_transform(entry, type, text_poke_early, 1); 142 } 143 144 #endif 145