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
19union jump_code_union {
20 char code[JUMP_LABEL_NOP_SIZE];
21 struct {
22 char jump;
23 int offset;
24 } __attribute__((packed));
25};
26
27static 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
38static 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
95void 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
103static 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}
131