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 *ideal_nop = ideal_nops[NOP_ATOMIC5]; 46 47 if (type == JUMP_LABEL_ENABLE) { 48 /* 49 * We are enabling this jump label. If it is not a nop 50 * then something must have gone wrong. 51 */ 52 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0)) 53 bug_at((void *)entry->code, __LINE__); 54 55 code.jump = 0xe9; 56 code.offset = entry->target - 57 (entry->code + JUMP_LABEL_NOP_SIZE); 58 } else { 59 /* 60 * We are disabling this jump label. If it is not what 61 * we think it is, then something must have gone wrong. 62 * If this is the first initialization call, then we 63 * are converting the default nop to the ideal nop. 64 */ 65 if (init) { 66 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 67 if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0)) 68 bug_at((void *)entry->code, __LINE__); 69 } else { 70 code.jump = 0xe9; 71 code.offset = entry->target - 72 (entry->code + JUMP_LABEL_NOP_SIZE); 73 if (unlikely(memcmp((void *)entry->code, &code, 5) != 0)) 74 bug_at((void *)entry->code, __LINE__); 75 } 76 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE); 77 } 78 79 /* 80 * Make text_poke_bp() a default fallback poker. 81 * 82 * At the time the change is being done, just ignore whether we 83 * are doing nop -> jump or jump -> nop transition, and assume 84 * always nop being the 'currently valid' instruction 85 * 86 */ 87 if (poker) 88 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE); 89 else 90 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE, 91 (void *)entry->code + JUMP_LABEL_NOP_SIZE); 92 } 93 94 void arch_jump_label_transform(struct jump_entry *entry, 95 enum jump_label_type type) 96 { 97 get_online_cpus(); 98 mutex_lock(&text_mutex); 99 __jump_label_transform(entry, type, NULL, 0); 100 mutex_unlock(&text_mutex); 101 put_online_cpus(); 102 } 103 104 static enum { 105 JL_STATE_START, 106 JL_STATE_NO_UPDATE, 107 JL_STATE_UPDATE, 108 } jlstate __initdata_or_module = JL_STATE_START; 109 110 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 111 enum jump_label_type type) 112 { 113 /* 114 * This function is called at boot up and when modules are 115 * first loaded. Check if the default nop, the one that is 116 * inserted at compile time, is the ideal nop. If it is, then 117 * we do not need to update the nop, and we can leave it as is. 118 * If it is not, then we need to update the nop to the ideal nop. 119 */ 120 if (jlstate == JL_STATE_START) { 121 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 122 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 123 124 if (memcmp(ideal_nop, default_nop, 5) != 0) 125 jlstate = JL_STATE_UPDATE; 126 else 127 jlstate = JL_STATE_NO_UPDATE; 128 } 129 if (jlstate == JL_STATE_UPDATE) 130 __jump_label_transform(entry, type, text_poke_early, 1); 131 } 132 133 #endif 134