arch/x86/kernel/jump_label.c

   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 #include <asm/text-patching.h>
  17
  18 #ifdef HAVE_JUMP_LABEL
  19
  20 union jump_code_union {
  21         char code[JUMP_LABEL_NOP_SIZE];
  22         struct {
  23                 char jump;
  24                 int offset;
  25         } __attribute__((packed));
  26 };
  27
  28 static void bug_at(unsigned char *ip, int line)
  29 {
  30         /*
  31          * The location is not an op that we were expecting.
  32          * Something went wrong. Crash the box, as something could be
  33          * corrupting the kernel.
  34          */
  35         pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, 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 default_nop[] = { STATIC_KEY_INIT_NOP };
  46         const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
  47
  48         if (type == JUMP_LABEL_JMP) {
  49                 if (init) {
  50                         /*
  51                          * Jump label is enabled for the first time.
  52                          * So we expect a default_nop...
  53                          */
  54                         if (unlikely(memcmp((void *)entry->code, default_nop, 5)
  55                                      != 0))
  56                                 bug_at((void *)entry->code, __LINE__);
  57                 } else {
  58                         /*
  59                          * ...otherwise expect an ideal_nop. Otherwise
  60                          * something went horribly wrong.
  61                          */
  62                         if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
  63                                      != 0))
  64                                 bug_at((void *)entry->code, __LINE__);
  65                 }
  66
  67                 code.jump = 0xe9;
  68                 code.offset = entry->target -
  69                                 (entry->code + JUMP_LABEL_NOP_SIZE);
  70         } else {
  71                 /*
  72                  * We are disabling this jump label. If it is not what
  73                  * we think it is, then something must have gone wrong.
  74                  * If this is the first initialization call, then we
  75                  * are converting the default nop to the ideal nop.
  76                  */
  77                 if (init) {
  78                         if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
  79                                 bug_at((void *)entry->code, __LINE__);
  80                 } else {
  81                         code.jump = 0xe9;
  82                         code.offset = entry->target -
  83                                 (entry->code + JUMP_LABEL_NOP_SIZE);
  84                         if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
  85                                 bug_at((void *)entry->code, __LINE__);
  86                 }
  87                 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
  88         }
  89
  90         /*
  91          * Make text_poke_bp() a default fallback poker.
  92          *
  93          * At the time the change is being done, just ignore whether we
  94          * are doing nop -> jump or jump -> nop transition, and assume
  95          * always nop being the 'currently valid' instruction
  96          *
  97          */
  98         if (poker)
  99                 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
 100         else
 101                 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
 102                              (void *)entry->code + JUMP_LABEL_NOP_SIZE);
 103 }
 104
 105 void arch_jump_label_transform(struct jump_entry *entry,
 106                                enum jump_label_type type)
 107 {
 108         mutex_lock(&text_mutex);
 109         __jump_label_transform(entry, type, NULL, 0);
 110         mutex_unlock(&text_mutex);
 111 }
 112
 113 static enum {
 114         JL_STATE_START,
 115         JL_STATE_NO_UPDATE,
 116         JL_STATE_UPDATE,
 117 } jlstate __initdata_or_module = JL_STATE_START;
 118
 119 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 120                                       enum jump_label_type type)
 121 {
 122         /*
 123          * This function is called at boot up and when modules are
 124          * first loaded. Check if the default nop, the one that is
 125          * inserted at compile time, is the ideal nop. If it is, then
 126          * we do not need to update the nop, and we can leave it as is.
 127          * If it is not, then we need to update the nop to the ideal nop.
 128          */
 129         if (jlstate == JL_STATE_START) {
 130                 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 131                 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 132
 133                 if (memcmp(ideal_nop, default_nop, 5) != 0)
 134                         jlstate = JL_STATE_UPDATE;
 135                 else
 136                         jlstate = JL_STATE_NO_UPDATE;
 137         }
 138         if (jlstate == JL_STATE_UPDATE)
 139                 __jump_label_transform(entry, type, text_poke_early, 1);
 140 }
 141
 142 #endif