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 __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         mutex_lock(&text_mutex);
 110         __jump_label_transform(entry, type, NULL, 0);
 111         mutex_unlock(&text_mutex);
 112 }
 113
 114 static enum {
 115         JL_STATE_START,
 116         JL_STATE_NO_UPDATE,
 117         JL_STATE_UPDATE,
 118 } jlstate __initdata_or_module = JL_STATE_START;
 119
 120 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 121                                       enum jump_label_type type)
 122 {
 123         /*
 124          * This function is called at boot up and when modules are
 125          * first loaded. Check if the default nop, the one that is
 126          * inserted at compile time, is the ideal nop. If it is, then
 127          * we do not need to update the nop, and we can leave it as is.
 128          * If it is not, then we need to update the nop to the ideal nop.
 129          */
 130         if (jlstate == JL_STATE_START) {
 131                 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 132                 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 133
 134                 if (memcmp(ideal_nop, default_nop, 5) != 0)
 135                         jlstate = JL_STATE_UPDATE;
 136                 else
 137                         jlstate = JL_STATE_NO_UPDATE;
 138         }
 139         if (jlstate == JL_STATE_UPDATE)
 140                 __jump_label_transform(entry, type, text_poke_early, 1);
 141 }
 142
 143 #endif