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
bug_at(unsigned char * ip,int line)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
__jump_label_transform(struct jump_entry * entry,enum jump_label_type type,void * (* poker)(void *,const void *,size_t),int init)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 code;
46 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
47 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
48
49 if (early_boot_irqs_disabled)
50 poker = text_poke_early;
51
52 if (type == JUMP_LABEL_JMP) {
53 if (init) {
54 /*
55 * Jump label is enabled for the first time.
56 * So we expect a default_nop...
57 */
58 if (unlikely(memcmp((void *)entry->code, default_nop, 5)
59 != 0))
60 bug_at((void *)entry->code, __LINE__);
61 } else {
62 /*
63 * ...otherwise expect an ideal_nop. Otherwise
64 * something went horribly wrong.
65 */
66 if (unlikely(memcmp((void *)entry->code, ideal_nop, 5)
67 != 0))
68 bug_at((void *)entry->code, __LINE__);
69 }
70
71 code.jump = 0xe9;
72 code.offset = entry->target -
73 (entry->code + JUMP_LABEL_NOP_SIZE);
74 } else {
75 /*
76 * We are disabling this jump label. If it is not what
77 * we think it is, then something must have gone wrong.
78 * If this is the first initialization call, then we
79 * are converting the default nop to the ideal nop.
80 */
81 if (init) {
82 if (unlikely(memcmp((void *)entry->code, default_nop, 5) != 0))
83 bug_at((void *)entry->code, __LINE__);
84 } else {
85 code.jump = 0xe9;
86 code.offset = entry->target -
87 (entry->code + JUMP_LABEL_NOP_SIZE);
88 if (unlikely(memcmp((void *)entry->code, &code, 5) != 0))
89 bug_at((void *)entry->code, __LINE__);
90 }
91 memcpy(&code, ideal_nops[NOP_ATOMIC5], JUMP_LABEL_NOP_SIZE);
92 }
93
94 /*
95 * Make text_poke_bp() a default fallback poker.
96 *
97 * At the time the change is being done, just ignore whether we
98 * are doing nop -> jump or jump -> nop transition, and assume
99 * always nop being the 'currently valid' instruction
100 *
101 */
102 if (poker)
103 (*poker)((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE);
104 else
105 text_poke_bp((void *)entry->code, &code, JUMP_LABEL_NOP_SIZE,
106 (void *)entry->code + JUMP_LABEL_NOP_SIZE);
107 }
108
arch_jump_label_transform(struct jump_entry * entry,enum jump_label_type type)109 void arch_jump_label_transform(struct jump_entry *entry,
110 enum jump_label_type type)
111 {
112 mutex_lock(&text_mutex);
113 __jump_label_transform(entry, type, NULL, 0);
114 mutex_unlock(&text_mutex);
115 }
116
117 static enum {
118 JL_STATE_START,
119 JL_STATE_NO_UPDATE,
120 JL_STATE_UPDATE,
121 } jlstate __initdata_or_module = JL_STATE_START;
122
arch_jump_label_transform_static(struct jump_entry * entry,enum jump_label_type type)123 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
124 enum jump_label_type type)
125 {
126 /*
127 * This function is called at boot up and when modules are
128 * first loaded. Check if the default nop, the one that is
129 * inserted at compile time, is the ideal nop. If it is, then
130 * we do not need to update the nop, and we can leave it as is.
131 * If it is not, then we need to update the nop to the ideal nop.
132 */
133 if (jlstate == JL_STATE_START) {
134 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
135 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
136
137 if (memcmp(ideal_nop, default_nop, 5) != 0)
138 jlstate = JL_STATE_UPDATE;
139 else
140 jlstate = JL_STATE_NO_UPDATE;
141 }
142 if (jlstate == JL_STATE_UPDATE)
143 __jump_label_transform(entry, type, text_poke_early, 1);
144 }
145
146 #endif
147
