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 jmp;
  46         const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
  47         const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
  48         const void *expect, *code;
  49         int line;
  50
  51         jmp.jump = 0xe9;
  52         jmp.offset = jump_entry_target(entry) -
  53                      (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
  54
  55         if (early_boot_irqs_disabled)
  56                 poker = text_poke_early;
  57
  58         if (type == JUMP_LABEL_JMP) {
  59                 if (init) {
  60                         expect = default_nop; line = __LINE__;
  61                 } else {
  62                         expect = ideal_nop; line = __LINE__;
  63                 }
  64
  65                 code = &jmp.code;
  66         } else {
  67                 if (init) {
  68                         expect = default_nop; line = __LINE__;
  69                 } else {
  70                         expect = &jmp.code; line = __LINE__;
  71                 }
  72
  73                 code = ideal_nop;
  74         }
  75
  76         if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
  77                 bug_at((void *)jump_entry_code(entry), line);
  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 *)jump_entry_code(entry), code,
  89                          JUMP_LABEL_NOP_SIZE);
  90                 return;
  91         }
  92
  93         text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE,
  94                      (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
  95 }
  96
  97 void arch_jump_label_transform(struct jump_entry *entry,
  98                                enum jump_label_type type)
  99 {
 100         mutex_lock(&text_mutex);
 101         __jump_label_transform(entry, type, NULL, 0);
 102         mutex_unlock(&text_mutex);
 103 }
 104
 105 static enum {
 106         JL_STATE_START,
 107         JL_STATE_NO_UPDATE,
 108         JL_STATE_UPDATE,
 109 } jlstate __initdata_or_module = JL_STATE_START;
 110
 111 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 112                                       enum jump_label_type type)
 113 {
 114         /*
 115          * This function is called at boot up and when modules are
 116          * first loaded. Check if the default nop, the one that is
 117          * inserted at compile time, is the ideal nop. If it is, then
 118          * we do not need to update the nop, and we can leave it as is.
 119          * If it is not, then we need to update the nop to the ideal nop.
 120          */
 121         if (jlstate == JL_STATE_START) {
 122                 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 123                 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 124
 125                 if (memcmp(ideal_nop, default_nop, 5) != 0)
 126                         jlstate = JL_STATE_UPDATE;
 127                 else
 128                         jlstate = JL_STATE_NO_UPDATE;
 129         }
 130         if (jlstate == JL_STATE_UPDATE)
 131                 __jump_label_transform(entry, type, text_poke_early, 1);
 132 }
 133
 134 #endif