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 #include <asm/text-patching.h> 17 18 #ifdef HAVE_JUMP_LABEL 19 20 union jump_code_union { 21 char code[JUMP_LABEL_NOP_SIZE]; 22 struct { 23 char jump; 24 int offset; 25 } __attribute__((packed)); 26 }; 27 28 static void bug_at(unsigned char *ip, int line) 29 { 30 /* 31 * The location is not an op that we were expecting. 32 * Something went wrong. Crash the box, as something could be 33 * corrupting the kernel. 34 */ 35 pr_warning("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n", 36 ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, line); 37 BUG(); 38 } 39 40 static void __jump_label_transform(struct jump_entry *entry, 41 enum jump_label_type type, 42 void *(*poker)(void *, const void *, size_t), 43 int init) 44 { 45 union jump_code_union code; 46 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 47 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 48 49 if (type == JUMP_LABEL_JMP) { 50 if (init) { 51 /* 52 * Jump label is enabled for the first time. 53 * So we expect a default_nop... 54 */ 55 if (unlikely(memcmp((void *)entry->code, default_nop, 5) 56 != 0)) 57 bug_at((void *)entry->code, __LINE__); 58 } else { 59 /* 60 * ...otherwise expect an ideal_nop. Otherwise 61 * something went horribly wrong. 62 */ 63 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) 64 != 0)) 65 bug_at((void *)entry->code, __LINE__); 66 } 67 68 code.jump = 0xe9; 69 code.offset = entry->target - 70 (entry->code + JUMP_LABEL_NOP_SIZE); 71 } else { 72 /* 73 * We are disabling this jump label. If it is not what 74 * we think it is, then something must have gone wrong. 75 * If this is the first initialization call, then we 76 * are converting the default nop to the ideal nop. 77 */ 78 if (init) { 79 if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) 80 bug_at((void *)entry->code, __LINE__); 81 } else { 82 code.jump = 0xe9; 83 code.offset = entry->target - 84 (entry->code + JUMP_LABEL_NOP_SIZE); 85 if (unlikely(memcmp((void *)entry->code, &code, 5) != 0)) 86 bug_at((void *)entry->code, __LINE__); 87 } 88 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); 89 } 90 91 /* 92 * Make text_poke_bp() a default fallback poker. 93 * 94 * At the time the change is being done, just ignore whether we 95 * are doing nop -> jump or jump -> nop transition, and assume 96 * always nop being the 'currently valid' instruction 97 * 98 */ 99 if (poker) 100 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); 101 else 102 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE, 103 (void *)entry->code + JUMP_LABEL_NOP_SIZE); 104 } 105 106 void arch_jump_label_transform(struct jump_entry *entry, 107 enum jump_label_type type) 108 { 109 get_online_cpus(); 110 mutex_lock(&text_mutex); 111 __jump_label_transform(entry, type, NULL, 0); 112 mutex_unlock(&text_mutex); 113 put_online_cpus(); 114 } 115 116 static enum { 117 JL_STATE_START, 118 JL_STATE_NO_UPDATE, 119 JL_STATE_UPDATE, 120 } jlstate __initdata_or_module = JL_STATE_START; 121 122 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 123 enum jump_label_type type) 124 { 125 /* 126 * This function is called at boot up and when modules are 127 * first loaded. Check if the default nop, the one that is 128 * inserted at compile time, is the ideal nop. If it is, then 129 * we do not need to update the nop, and we can leave it as is. 130 * If it is not, then we need to update the nop to the ideal nop. 131 */ 132 if (jlstate == JL_STATE_START) { 133 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 134 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 135 136 if (memcmp(ideal_nop, default_nop, 5) != 0) 137 jlstate = JL_STATE_UPDATE; 138 else 139 jlstate = JL_STATE_NO_UPDATE; 140 } 141 if (jlstate == JL_STATE_UPDATE) 142 __jump_label_transform(entry, type, text_poke_early, 1); 143 } 144 145 #endif 146