xref: /openbmc/linux/arch/x86/kernel/jump_label.c (revision 7e6b9db2)
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 #include <asm/insn.h>
19 
arch_jump_entry_size(struct jump_entry * entry)20 int arch_jump_entry_size(struct jump_entry *entry)
21 {
22 	struct insn insn = {};
23 
24 	insn_decode_kernel(&insn, (void *)jump_entry_code(entry));
25 	BUG_ON(insn.length != 2 && insn.length != 5);
26 
27 	return insn.length;
28 }
29 
30 struct jump_label_patch {
31 	const void *code;
32 	int size;
33 };
34 
35 static struct jump_label_patch
__jump_label_patch(struct jump_entry * entry,enum jump_label_type type)36 __jump_label_patch(struct jump_entry *entry, enum jump_label_type type)
37 {
38 	const void *expect, *code, *nop;
39 	const void *addr, *dest;
40 	int size;
41 
42 	addr = (void *)jump_entry_code(entry);
43 	dest = (void *)jump_entry_target(entry);
44 
45 	size = arch_jump_entry_size(entry);
46 	switch (size) {
47 	case JMP8_INSN_SIZE:
48 		code = text_gen_insn(JMP8_INSN_OPCODE, addr, dest);
49 		nop = x86_nops[size];
50 		break;
51 
52 	case JMP32_INSN_SIZE:
53 		code = text_gen_insn(JMP32_INSN_OPCODE, addr, dest);
54 		nop = x86_nops[size];
55 		break;
56 
57 	default: BUG();
58 	}
59 
60 	if (type == JUMP_LABEL_JMP)
61 		expect = nop;
62 	else
63 		expect = code;
64 
65 	if (memcmp(addr, expect, size)) {
66 		/*
67 		 * The location is not an op that we were expecting.
68 		 * Something went wrong. Crash the box, as something could be
69 		 * corrupting the kernel.
70 		 */
71 		pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph != %5ph)) size:%d type:%d\n",
72 				addr, addr, addr, expect, size, type);
73 		BUG();
74 	}
75 
76 	if (type == JUMP_LABEL_NOP)
77 		code = nop;
78 
79 	return (struct jump_label_patch){.code = code, .size = size};
80 }
81 
82 static __always_inline void
__jump_label_transform(struct jump_entry * entry,enum jump_label_type type,int init)83 __jump_label_transform(struct jump_entry *entry,
84 		       enum jump_label_type type,
85 		       int init)
86 {
87 	const struct jump_label_patch jlp = __jump_label_patch(entry, type);
88 
89 	/*
90 	 * As long as only a single processor is running and the code is still
91 	 * not marked as RO, text_poke_early() can be used; Checking that
92 	 * system_state is SYSTEM_BOOTING guarantees it. It will be set to
93 	 * SYSTEM_SCHEDULING before other cores are awaken and before the
94 	 * code is write-protected.
95 	 *
96 	 * At the time the change is being done, just ignore whether we
97 	 * are doing nop -> jump or jump -> nop transition, and assume
98 	 * always nop being the 'currently valid' instruction
99 	 */
100 	if (init || system_state == SYSTEM_BOOTING) {
101 		text_poke_early((void *)jump_entry_code(entry), jlp.code, jlp.size);
102 		return;
103 	}
104 
105 	text_poke_bp((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL);
106 }
107 
jump_label_transform(struct jump_entry * entry,enum jump_label_type type,int init)108 static void __ref jump_label_transform(struct jump_entry *entry,
109 				       enum jump_label_type type,
110 				       int init)
111 {
112 	mutex_lock(&text_mutex);
113 	__jump_label_transform(entry, type, init);
114 	mutex_unlock(&text_mutex);
115 }
116 
arch_jump_label_transform(struct jump_entry * entry,enum jump_label_type type)117 void arch_jump_label_transform(struct jump_entry *entry,
118 			       enum jump_label_type type)
119 {
120 	jump_label_transform(entry, type, 0);
121 }
122 
arch_jump_label_transform_queue(struct jump_entry * entry,enum jump_label_type type)123 bool arch_jump_label_transform_queue(struct jump_entry *entry,
124 				     enum jump_label_type type)
125 {
126 	struct jump_label_patch jlp;
127 
128 	if (system_state == SYSTEM_BOOTING) {
129 		/*
130 		 * Fallback to the non-batching mode.
131 		 */
132 		arch_jump_label_transform(entry, type);
133 		return true;
134 	}
135 
136 	mutex_lock(&text_mutex);
137 	jlp = __jump_label_patch(entry, type);
138 	text_poke_queue((void *)jump_entry_code(entry), jlp.code, jlp.size, NULL);
139 	mutex_unlock(&text_mutex);
140 	return true;
141 }
142 
arch_jump_label_transform_apply(void)143 void arch_jump_label_transform_apply(void)
144 {
145 	mutex_lock(&text_mutex);
146 	text_poke_finish();
147 	mutex_unlock(&text_mutex);
148 }
149