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, NULL);
95 void arch_jump_label_transform(struct jump_entry *entry,
96 enum jump_label_type type)
98 mutex_lock(&text_mutex);
99 __jump_label_transform(entry, type, 0);
100 mutex_unlock(&text_mutex);
103 #define TP_VEC_MAX (PAGE_SIZE / sizeof(struct text_poke_loc))
104 static struct text_poke_loc tp_vec[TP_VEC_MAX];
105 static int tp_vec_nr;
107 bool arch_jump_label_transform_queue(struct jump_entry *entry,
108 enum jump_label_type type)
110 struct text_poke_loc *tp;
113 if (system_state == SYSTEM_BOOTING) {
115 * Fallback to the non-batching mode.
117 arch_jump_label_transform(entry, type);
122 * No more space in the vector, tell upper layer to apply
123 * the queue before continuing.
125 if (tp_vec_nr == TP_VEC_MAX)
128 tp = &tp_vec[tp_vec_nr];
130 entry_code = (void *)jump_entry_code(entry);
133 * The INT3 handler will do a bsearch in the queue, so we need entries
134 * to be sorted. We can survive an unsorted list by rejecting the entry,
135 * forcing the generic jump_label code to apply the queue. Warning once,
136 * to raise the attention to the case of an unsorted entry that is
137 * better not happen, because, in the worst case we will perform in the
138 * same way as we do without batching - with some more overhead.
141 int prev = tp_vec_nr - 1;
142 struct text_poke_loc *prev_tp = &tp_vec[prev];
144 if (WARN_ON_ONCE(prev_tp->addr > entry_code))
148 __jump_label_set_jump_code(entry, type,
149 (union jump_code_union *)&tp->text, 0);
151 text_poke_loc_init(tp, entry_code, NULL, JUMP_LABEL_NOP_SIZE, NULL);
158 void arch_jump_label_transform_apply(void)
163 mutex_lock(&text_mutex);
164 text_poke_bp_batch(tp_vec, tp_vec_nr);
165 mutex_unlock(&text_mutex);
174 } jlstate __initdata_or_module = JL_STATE_START;
176 __init_or_module void arch_jump_label_transform_static(struct jump_entry *entry,
177 enum jump_label_type type)
180 * This function is called at boot up and when modules are
181 * first loaded. Check if the default nop, the one that is
182 * inserted at compile time, is the ideal nop. If it is, then
183 * we do not need to update the nop, and we can leave it as is.
184 * If it is not, then we need to update the nop to the ideal nop.
186 if (jlstate == JL_STATE_START) {
187 const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP };
188 const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5];
190 if (memcmp(ideal_nop, default_nop, 5) != 0)
191 jlstate = JL_STATE_UPDATE;
193 jlstate = JL_STATE_NO_UPDATE;
195 if (jlstate == JL_STATE_UPDATE)
196 __jump_label_transform(entry, type, 1);