1 // SPDX-License-Identifier: GPL-2.0
3 * jump label x86 support
5 * Copyright (C) 2009 Jason Baron <jbaron@redhat.com>
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>
19 union jump_code_union {
20 char code[JUMP_LABEL_NOP_SIZE];
24 } __attribute__((packed));
27 static void bug_at(unsigned char *ip, int line)
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.
34 pr_crit("jump_label: Fatal kernel bug, unexpected op at %pS [%p] (%5ph) %d\n", ip, ip, ip, line);
38 static void __jump_label_set_jump_code(struct jump_entry *entry,
39 enum jump_label_type type,
40 union jump_code_union *code,
43 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
44 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
49 code->offset = jump_entry_target(entry) -
50 (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
53 expect = default_nop; line = __LINE__;
54 } else if (type == JUMP_LABEL_JMP) {
55 expect = ideal_nop; line = __LINE__;
57 expect = code->code; line = __LINE__;
60 if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE))
61 bug_at((void *)jump_entry_code(entry), line);
63 if (type == JUMP_LABEL_NOP)
64 memcpy(code, ideal_nop, JUMP_LABEL_NOP_SIZE);
67 static void __ref __jump_label_transform(struct jump_entry *entry,
68 enum jump_label_type type,
71 union jump_code_union code;
73 __jump_label_set_jump_code(entry, type, &code, init);
76 * As long as only a single processor is running and the code is still
77 * not marked as RO, text_poke_early() can be used; Checking that
78 * system_state is SYSTEM_BOOTING guarantees it. It will be set to
79 * SYSTEM_SCHEDULING before other cores are awaken and before the
80 * code is write-protected.
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
86 if (init || system_state == SYSTEM_BOOTING) {
87 text_poke_early((void *)jump_entry_code(entry), &code,
92 text_poke_bp((void *)jump_entry_code(entry), &code, JUMP_LABEL_NOP_SIZE,
93 (void *)jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE);
96 void arch_jump_label_transform(struct jump_entry *entry,
97 enum jump_label_type type)
99 mutex_lock(&text_mutex);
100 __jump_label_transform(entry, type, 0);
101 mutex_unlock(&text_mutex);
104 #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
105 static struct text_poke_loc tp_vec[TP_VEC_MAX];
106 static int tp_vec_nr;
108 bool arch_jump_label_transform_queue(struct jump_entry *entry,
109 enum jump_label_type type)
111 struct text_poke_loc *tp;
114 if (system_state == SYSTEM_BOOTING) {
116 * Fallback to the non-batching mode.
118 arch_jump_label_transform(entry, type);
123 * No more space in the vector, tell upper layer to apply
124 * the queue before continuing.
126 if (tp_vec_nr == TP_VEC_MAX)
129 tp = &tp_vec[tp_vec_nr];
131 entry_code = (void *)jump_entry_code(entry);
134 * The INT3 handler will do a bsearch in the queue, so we need entries
135 * to be sorted. We can survive an unsorted list by rejecting the entry,
136 * forcing the generic jump_label code to apply the queue. Warning once,
137 * to raise the attention to the case of an unsorted entry that is
138 * better not happen, because, in the worst case we will perform in the
139 * same way as we do without batching - with some more overhead.
142 int prev = tp_vec_nr - 1;
143 struct text_poke_loc *prev_tp = &tp_vec[prev];
145 if (WARN_ON_ONCE(prev_tp->addr > entry_code))
149 __jump_label_set_jump_code(entry, type,
150 (union jump_code_union *) &tp->opcode, 0);
152 tp->addr = entry_code;
153 tp->detour = entry_code + JUMP_LABEL_NOP_SIZE;
154 tp->len = JUMP_LABEL_NOP_SIZE;
161 void arch_jump_label_transform_apply(void)
166 mutex_lock(&text_mutex);
167 text_poke_bp_batch(tp_vec, tp_vec_nr);
168 mutex_unlock(&text_mutex);
177 } jlstate __initdata_or_module = JL_STATE_START;
179 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
180 enum jump_label_type type)
183 * This function is called at boot up and when modules are
184 * first loaded. Check if the default nop, the one that is
185 * inserted at compile time, is the ideal nop. If it is, then
186 * we do not need to update the nop, and we can leave it as is.
187 * If it is not, then we need to update the nop to the ideal nop.
189 if (jlstate == JL_STATE_START) {
190 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
191 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
193 if (memcmp(ideal_nop, default_nop, 5) != 0)
194 jlstate = JL_STATE_UPDATE;
196 jlstate = JL_STATE_NO_UPDATE;
198 if (jlstate == JL_STATE_UPDATE)
199 __jump_label_transform(entry, type, 1);