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 __jump_label_set_jump_code(struct jump_entry *entry, 39 enum jump_label_type type, 40 union jump_code_union *code, 41 int init) 42 { 43 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 44 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 45 const void *expect; 46 int line; 47 48 code->jump = 0xe9; 49 code->offset = jump_entry_target(entry) - 50 (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); 51 52 if (init) { 53 expect = default_nop; line = __LINE__; 54 } else if (type == JUMP_LABEL_JMP) { 55 expect = ideal_nop; line = __LINE__; 56 } else { 57 expect = code->code; line = __LINE__; 58 } 59 60 if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE)) 61 bug_at((void *)jump_entry_code(entry), line); 62 63 if (type == JUMP_LABEL_NOP) 64 memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE); 65 } 66 67 static void __ref __jump_label_transform(struct jump_entry *entry, 68 enum jump_label_type type, 69 int init) 70 { 71 union jump_code_union code; 72 73 __jump_label_set_jump_code(entry, type, &code, init); 74 75 /* 76 * As long as only a single processor is running and the code is still 77 * not marked as RO, text_poke_early() can be used; Checking that 78 * system_state is SYSTEM_BOOTING guarantees it. It will be set to 79 * SYSTEM_SCHEDULING before other cores are awaken and before the 80 * code is write-protected. 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 if (init || system_state == SYSTEM_BOOTING) { 87 text_poke_early((void *)jump_entry_code(entry), &code, 88 JUMP_LABEL_NOP_SIZE); 89 return; 90 } 91 92 text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE, NULL); 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, 0); 100 mutex_unlock(&text_mutex); 101 } 102 103 #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc)) 104 static struct text_poke_loc tp_vec[TP_VEC_MAX]; 105 static int tp_vec_nr; 106 107 bool arch_jump_label_transform_queue(struct jump_entry *entry, 108 enum jump_label_type type) 109 { 110 struct text_poke_loc *tp; 111 void *entry_code; 112 113 if (system_state == SYSTEM_BOOTING) { 114 /* 115 * Fallback to the non-batching mode. 116 */ 117 arch_jump_label_transform(entry, type); 118 return true; 119 } 120 121 /* 122 * No more space in the vector, tell upper layer to apply 123 * the queue before continuing. 124 */ 125 if (tp_vec_nr == TP_VEC_MAX) 126 return false; 127 128 tp = &tp_vec[tp_vec_nr]; 129 130 entry_code = (void *)jump_entry_code(entry); 131 132 /* 133 * The INT3 handler will do a bsearch in the queue, so we need entries 134 * to be sorted. We can survive an unsorted list by rejecting the entry, 135 * forcing the generic jump_label code to apply the queue. Warning once, 136 * to raise the attention to the case of an unsorted entry that is 137 * better not happen, because, in the worst case we will perform in the 138 * same way as we do without batching - with some more overhead. 139 */ 140 if (tp_vec_nr > 0) { 141 int prev = tp_vec_nr - 1; 142 struct text_poke_loc *prev_tp = &tp_vec[prev]; 143 144 if (WARN_ON_ONCE(prev_tp->addr > entry_code)) 145 return false; 146 } 147 148 __jump_label_set_jump_code(entry, type, 149 (union jump_code_union *)&tp->text, 0); 150 151 text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL); 152 153 tp_vec_nr++; 154 155 return true; 156 } 157 158 void arch_jump_label_transform_apply(void) 159 { 160 if (!tp_vec_nr) 161 return; 162 163 mutex_lock(&text_mutex); 164 text_poke_bp_batch(tp_vec, tp_vec_nr); 165 mutex_unlock(&text_mutex); 166 167 tp_vec_nr = 0; 168 } 169 170 static enum { 171 JL_STATE_START, 172 JL_STATE_NO_UPDATE, 173 JL_STATE_UPDATE, 174 } jlstate __initdata_or_module = JL_STATE_START; 175 176 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry, 177 enum jump_label_type type) 178 { 179 /* 180 * This function is called at boot up and when modules are 181 * first loaded. Check if the default nop, the one that is 182 * inserted at compile time, is the ideal nop. If it is, then 183 * we do not need to update the nop, and we can leave it as is. 184 * If it is not, then we need to update the nop to the ideal nop. 185 */ 186 if (jlstate == JL_STATE_START) { 187 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; 188 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; 189 190 if (memcmp(ideal_nop, default_nop, 5) != 0) 191 jlstate = JL_STATE_UPDATE; 192 else 193 jlstate = JL_STATE_NO_UPDATE; 194 } 195 if (jlstate == JL_STATE_UPDATE) 196 __jump_label_transform(entry, type, 1); 197 } 198