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 jmp;
  44         const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
  45         const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
  46         const void *expect, *code;
  47         int line;
  48
  49         jmp.jump = 0xe9;
  50         jmp.offset = jump_entry_target(entry) -
  51                      (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
  52
  53         if (early_boot_irqs_disabled)
  54                 poker = text_poke_early;
  55
  56         if (type == JUMP_LABEL_JMP) {
  57                 if (init) {
  58                         expect = default_nop; line = __LINE__;
  59                 } else {
  60                         expect = ideal_nop; line = __LINE__;
  61                 }
  62
  63                 code = &jmp.code;
  64         } else {
  65                 if (init) {
  66                         expect = default_nop; line = __LINE__;
  67                 } else {
  68                         expect = &jmp.code; line = __LINE__;
  69                 }
  70
  71                 code = ideal_nop;
  72         }
  73
  74         if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
  75                 bug_at((void *)jump_entry_code(entry), line);
  76
  77         /*
  78          * Make text_poke_bp() a default fallback poker.
  79          *
  80          * At the time the change is being done, just ignore whether we
  81          * are doing nop -> jump or jump -> nop transition, and assume
  82          * always nop being the 'currently valid' instruction
  83          *
  84          */
  85         if (poker) {
  86                 (*poker)((void *)jump_entry_code(entry), code,
  87                          JUMP_LABEL_NOP_SIZE);
  88                 return;
  89         }
  90
  91         text_poke_bp((void *)jump_entry_code(entry), code, JUMP_LABEL_NOP_SIZE,
  92                      (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
  93 }
  94
  95 void arch_jump_label_transform(struct jump_entry *entry,
  96                                enum jump_label_type type)
  97 {
  98         mutex_lock(&text_mutex);
  99         __jump_label_transform(entry, type, NULL, 0);
 100         mutex_unlock(&text_mutex);
 101 }
 102
 103 static enum {
 104         JL_STATE_START,
 105         JL_STATE_NO_UPDATE,
 106         JL_STATE_UPDATE,
 107 } jlstate __initdata_or_module = JL_STATE_START;
 108
 109 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
 110                                       enum jump_label_type type)
 111 {
 112         /*
 113          * This function is called at boot up and when modules are
 114          * first loaded. Check if the default nop, the one that is
 115          * inserted at compile time, is the ideal nop. If it is, then
 116          * we do not need to update the nop, and we can leave it as is.
 117          * If it is not, then we need to update the nop to the ideal nop.
 118          */
 119         if (jlstate == JL_STATE_START) {
 120                 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
 121                 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
 122
 123                 if (memcmp(ideal_nop, default_nop, 5) != 0)
 124                         jlstate = JL_STATE_UPDATE;
 125                 else
 126                         jlstate = JL_STATE_NO_UPDATE;
 127         }
 128         if (jlstate == JL_STATE_UPDATE)
 129                 __jump_label_transform(entry, type, text_poke_early, 1);
 130 }