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 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 __ref __jump_label_transform(struct jump_entry *entry,
  39                                          enum jump_label_type type,
  40                                          void *(*poker)(void *, const void *, size_t),
  41                                          int init)
  42 {
  43         union jump_code_union code;
  44         const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
  45         const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
  46
  47         if (early_boot_irqs_disabled)
  48                 poker = text_poke_early;
  49
  50         if (type == JUMP_LABEL_JMP) {
  51                 if (init) {
  52                         /*
  53                          * Jump label is enabled for the first time.
  54                          * So we expect a default_nop...
  55                          */
  56                         if (unlikely(memcmp((void *)entry->code, default_nop, 5)
  57                                      != 0))
  58                                 bug_at((void *)entry->code, __LINE__);
  59                 } else {
  60                         /*
  61                          * ...otherwise expect an ideal_nop. Otherwise
  62                          * something went horribly wrong.
  63                          */
  64                         if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
  65                                      != 0))
  66                                 bug_at((void *)entry->code, __LINE__);
  67                 }
  68
  69                 code.jump = 0xe9;
  70                 code.offset = entry->target -
  71                                 (entry->code + JUMP_LABEL_NOP_SIZE);
  72         } else {
  73                 /*
  74                  * We are disabling this jump label. If it is not what
  75                  * we think it is, then something must have gone wrong.
  76                  * If this is the first initialization call, then we
  77                  * are converting the default nop to the ideal nop.
  78                  */
  79                 if (init) {
  80                         if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
  81                                 bug_at((void *)entry->code, __LINE__);
  82                 } else {
  83                         code.jump = 0xe9;
  84                         code.offset = entry->target -
  85                                 (entry->code + JUMP_LABEL_NOP_SIZE);
  86                         if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
  87                                 bug_at((void *)entry->code, __LINE__);
  88                 }
  89                 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
  90         }
  91
  92         /*
  93          * Make text_poke_bp() a default fallback poker.
  94          *
  95          * At the time the change is being done, just ignore whether we
  96          * are doing nop -> jump or jump -> nop transition, and assume
  97          * always nop being the 'currently valid' instruction
  98          *
  99          */
 100         if (poker)
 101                 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
 102         else
 103                 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
 104                              (void *)entry->code + JUMP_LABEL_NOP_SIZE);
 105 }
 106
 107 void arch_jump_label_transform(struct jump_entry *entry,
 108                                enum jump_label_type type)
 109 {
 110         mutex_lock(&text_mutex);
 111         __jump_label_transform(entry, type, NULL, 0);
 112         mutex_unlock(&text_mutex);
 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 }