1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef _ASM_X86_TEXT_PATCHING_H
3#define _ASM_X86_TEXT_PATCHING_H
4
5#include <linux/types.h>
6#include <linux/stddef.h>
7#include <asm/ptrace.h>
8
9struct paravirt_patch_site;
10#ifdef CONFIG_PARAVIRT
11void apply_paravirt(struct paravirt_patch_site *start,
12 struct paravirt_patch_site *end);
13#else
14static inline void apply_paravirt(struct paravirt_patch_site *start,
15 struct paravirt_patch_site *end)
16{}
17#define __parainstructions NULL
18#define __parainstructions_end NULL
19#endif
20
21/*
22 * Currently, the max observed size in the kernel code is
23 * JUMP_LABEL_NOP_SIZE/RELATIVEJUMP_SIZE, which are 5.
24 * Raise it if needed.
25 */
26#define POKE_MAX_OPCODE_SIZE 5
27
28extern void text_poke_early(void *addr, const void *opcode, size_t len);
29
30/*
31 * Clear and restore the kernel write-protection flag on the local CPU.
32 * Allows the kernel to edit read-only pages.
33 * Side-effect: any interrupt handler running between save and restore will have
34 * the ability to write to read-only pages.
35 *
36 * Warning:
37 * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
38 * no thread can be preempted in the instructions being modified (no iret to an
39 * invalid instruction possible) or if the instructions are changed from a
40 * consistent state to another consistent state atomically.
41 * On the local CPU you need to be protected against NMI or MCE handlers seeing
42 * an inconsistent instruction while you patch.
43 */
44extern void *text_poke(void *addr, const void *opcode, size_t len);
45extern void text_poke_sync(void);
46extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
47extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
48extern void *text_poke_copy_locked(void *addr, const void *opcode, size_t len, bool core_ok);
49extern void *text_poke_set(void *addr, int c, size_t len);
50extern int poke_int3_handler(struct pt_regs *regs);
51extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
52
53extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate);
54extern void text_poke_finish(void);
55
56#define INT3_INSN_SIZE 1
57#define INT3_INSN_OPCODE 0xCC
58
59#define RET_INSN_SIZE 1
60#define RET_INSN_OPCODE 0xC3
61
62#define CALL_INSN_SIZE 5
63#define CALL_INSN_OPCODE 0xE8
64
65#define JMP32_INSN_SIZE 5
66#define JMP32_INSN_OPCODE 0xE9
67
68#define JMP8_INSN_SIZE 2
69#define JMP8_INSN_OPCODE 0xEB
70
71#define DISP32_SIZE 4
72
73static __always_inline int text_opcode_size(u8 opcode)
74{
75 int size = 0;
76
77#define __CASE(insn) \
78 case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
79
80 switch(opcode) {
81 __CASE(INT3);
82 __CASE(RET);
83 __CASE(CALL);
84 __CASE(JMP32);
85 __CASE(JMP8);
86 }
87
88#undef __CASE
89
90 return size;
91}
92
93union text_poke_insn {
94 u8 text[POKE_MAX_OPCODE_SIZE];
95 struct {
96 u8 opcode;
97 s32 disp;
98 } __attribute__((packed));
99};
100
101static __always_inline
102void __text_gen_insn(void *buf, u8 opcode, const void *addr, const void *dest, int size)
103{
104 union text_poke_insn *insn = buf;
105
106 BUG_ON(size < text_opcode_size(opcode));
107
108 /*
109 * Hide the addresses to avoid the compiler folding in constants when
110 * referencing code, these can mess up annotations like
111 * ANNOTATE_NOENDBR.
112 */
113 OPTIMIZER_HIDE_VAR(insn);
114 OPTIMIZER_HIDE_VAR(addr);
115 OPTIMIZER_HIDE_VAR(dest);
116
117 insn->opcode = opcode;
118
119 if (size > 1) {
120 insn->disp = (long)dest - (long)(addr + size);
121 if (size == 2) {
122 /*
123 * Ensure that for JMP8 the displacement
124 * actually fits the signed byte.
125 */
126 BUG_ON((insn->disp >> 31) != (insn->disp >> 7));
127 }
128 }
129}
130
131static __always_inline
132void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
133{
134 static union text_poke_insn insn; /* per instance */
135 __text_gen_insn(buf: &insn, opcode, addr, dest, size: text_opcode_size(opcode));
136 return &insn.text;
137}
138
139extern int after_bootmem;
140extern __ro_after_init struct mm_struct *poking_mm;
141extern __ro_after_init unsigned long poking_addr;
142
143#ifndef CONFIG_UML_X86
144static __always_inline
145void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
146{
147 regs->ip = ip;
148}
149
150static __always_inline
151void int3_emulate_push(struct pt_regs *regs, unsigned long val)
152{
153 /*
154 * The int3 handler in entry_64.S adds a gap between the
155 * stack where the break point happened, and the saving of
156 * pt_regs. We can extend the original stack because of
157 * this gap. See the idtentry macro's create_gap option.
158 *
159 * Similarly entry_32.S will have a gap on the stack for (any) hardware
160 * exception and pt_regs; see FIXUP_FRAME.
161 */
162 regs->sp -= sizeof(unsigned long);
163 *(unsigned long *)regs->sp = val;
164}
165
166static __always_inline
167unsigned long int3_emulate_pop(struct pt_regs *regs)
168{
169 unsigned long val = *(unsigned long *)regs->sp;
170 regs->sp += sizeof(unsigned long);
171 return val;
172}
173
174static __always_inline
175void int3_emulate_call(struct pt_regs *regs, unsigned long func)
176{
177 int3_emulate_push(regs, val: regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
178 int3_emulate_jmp(regs, ip: func);
179}
180
181static __always_inline
182void int3_emulate_ret(struct pt_regs *regs)
183{
184 unsigned long ip = int3_emulate_pop(regs);
185 int3_emulate_jmp(regs, ip);
186}
187
188static __always_inline
189void int3_emulate_jcc(struct pt_regs *regs, u8 cc, unsigned long ip, unsigned long disp)
190{
191 static const unsigned long jcc_mask[6] = {
192 [0] = X86_EFLAGS_OF,
193 [1] = X86_EFLAGS_CF,
194 [2] = X86_EFLAGS_ZF,
195 [3] = X86_EFLAGS_CF | X86_EFLAGS_ZF,
196 [4] = X86_EFLAGS_SF,
197 [5] = X86_EFLAGS_PF,
198 };
199
200 bool invert = cc & 1;
201 bool match;
202
203 if (cc < 0xc) {
204 match = regs->flags & jcc_mask[cc >> 1];
205 } else {
206 match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^
207 ((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT);
208 if (cc >= 0xe)
209 match = match || (regs->flags & X86_EFLAGS_ZF);
210 }
211
212 if ((match && !invert) || (!match && invert))
213 ip += disp;
214
215 int3_emulate_jmp(regs, ip);
216}
217
218#endif /* !CONFIG_UML_X86 */
219
220#endif /* _ASM_X86_TEXT_PATCHING_H */
221

source code of linux/arch/x86/include/asm/text-patching.h