arch/x86/kernel/jump_label.c

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