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
  17 #ifdef HAVE_JUMP_LABEL
  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_warning("Unexpected op at %pS [%p] (%02x %02x %02x %02x %02x) %s:%d\n",
  35                ip, ip, ip[0], ip[1], ip[2], ip[3], ip[4], __FILE__, 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 *ideal_nop = ideal_nops[NOP_ATOMIC5];
  46
  47         if (type == JUMP_LABEL_ENABLE) {
  48                 /*
  49                  * We are enabling this jump label. If it is not a nop
  50                  * then something must have gone wrong.
  51                  */
  52                 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5) != 0))
  53                         bug_at((void *)entry->code, __LINE__);
  54
  55                 code.jump = 0xe9;
  56                 code.offset = entry->target -
  57                                 (entry->code + JUMP_LABEL_NOP_SIZE);
  58         } else {
  59                 /*
  60                  * We are disabling this jump label. If it is not what
  61                  * we think it is, then something must have gone wrong.
  62                  * If this is the first initialization call, then we
  63                  * are converting the default nop to the ideal nop.
  64                  */
  65                 if (init) {
  66                         const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
  67                         if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
  68                                 bug_at((void *)entry->code, __LINE__);
  69                 } else {
  70                         code.jump = 0xe9;
  71                         code.offset = entry->target -
  72                                 (entry->code + JUMP_LABEL_NOP_SIZE);
  73                         if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
  74                                 bug_at((void *)entry->code, __LINE__);
  75                 }
  76                 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
  77         }
  78
  79         /*
  80          * Make text_poke_bp() a default fallback poker.
  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          */
  87         if (poker)
  88                 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
  89         else
  90                 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
  91                              (void *)entry->code + JUMP_LABEL_NOP_SIZE);
  92 }
  93
  94 void arch_jump_label_transform(struct jump_entry *entry,
  95                                enum jump_label_type type)
  96 {
  97         get_online_cpus();
  98         mutex_lock(&text_mutex);
  99         __jump_label_transform(entry, type, NULL, 0);
 100         mutex_unlock(&text_mutex);
 101         put_online_cpus();
 102 }
 103
 104 static enum {
 105         JL_STATE_START,
 106         JL_STATE_NO_UPDATE,
 107         JL_STATE_UPDATE,
 108 } jlstate __initdata_or_module = JL_STATE_START;
 109
 110 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 111                                       enum jump_label_type type)
 112 {
 113         /*
 114          * This function is called at boot up and when modules are
 115          * first loaded. Check if the default nop, the one that is
 116          * inserted at compile time, is the ideal nop. If it is, then
 117          * we do not need to update the nop, and we can leave it as is.
 118          * If it is not, then we need to update the nop to the ideal nop.
 119          */
 120         if (jlstate == JL_STATE_START) {
 121                 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 122                 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 123
 124                 if (memcmp(ideal_nop, default_nop, 5) != 0)
 125                         jlstate = JL_STATE_UPDATE;
 126                 else
 127                         jlstate = JL_STATE_NO_UPDATE;
 128         }
 129         if (jlstate == JL_STATE_UPDATE)
 130                 __jump_label_transform(entry, type, text_poke_early, 1);
 131 }
 132
 133 #endif