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 
9 struct paravirt_patch_site;
10 #ifdef CONFIG_PARAVIRT
11 void apply_paravirt(struct paravirt_patch_site *start,
12 		    struct paravirt_patch_site *end);
13 #else
apply_paravirt(struct paravirt_patch_site * start,struct paravirt_patch_site * end)14 static 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 
28 extern 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  */
44 extern void *text_poke(void *addr, const void *opcode, size_t len);
45 extern void text_poke_sync(void);
46 extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
47 extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
48 extern void *text_poke_set(void *addr, int c, size_t len);
49 extern int poke_int3_handler(struct pt_regs *regs);
50 extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
51 
52 extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate);
53 extern void text_poke_finish(void);
54 
55 #define INT3_INSN_SIZE		1
56 #define INT3_INSN_OPCODE	0xCC
57 
58 #define RET_INSN_SIZE		1
59 #define RET_INSN_OPCODE		0xC3
60 
61 #define CALL_INSN_SIZE		5
62 #define CALL_INSN_OPCODE	0xE8
63 
64 #define JMP32_INSN_SIZE		5
65 #define JMP32_INSN_OPCODE	0xE9
66 
67 #define JMP8_INSN_SIZE		2
68 #define JMP8_INSN_OPCODE	0xEB
69 
70 #define DISP32_SIZE		4
71 
text_opcode_size(u8 opcode)72 static __always_inline int text_opcode_size(u8 opcode)
73 {
74 	int size = 0;
75 
76 #define __CASE(insn)	\
77 	case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
78 
79 	switch(opcode) {
80 	__CASE(INT3);
81 	__CASE(RET);
82 	__CASE(CALL);
83 	__CASE(JMP32);
84 	__CASE(JMP8);
85 	}
86 
87 #undef __CASE
88 
89 	return size;
90 }
91 
92 union text_poke_insn {
93 	u8 text[POKE_MAX_OPCODE_SIZE];
94 	struct {
95 		u8 opcode;
96 		s32 disp;
97 	} __attribute__((packed));
98 };
99 
100 static __always_inline
__text_gen_insn(void * buf,u8 opcode,const void * addr,const void * dest,int size)101 void __text_gen_insn(void *buf, u8 opcode, const void *addr, const void *dest, int size)
102 {
103 	union text_poke_insn *insn = buf;
104 
105 	BUG_ON(size < text_opcode_size(opcode));
106 
107 	/*
108 	 * Hide the addresses to avoid the compiler folding in constants when
109 	 * referencing code, these can mess up annotations like
110 	 * ANNOTATE_NOENDBR.
111 	 */
112 	OPTIMIZER_HIDE_VAR(insn);
113 	OPTIMIZER_HIDE_VAR(addr);
114 	OPTIMIZER_HIDE_VAR(dest);
115 
116 	insn->opcode = opcode;
117 
118 	if (size > 1) {
119 		insn->disp = (long)dest - (long)(addr + size);
120 		if (size == 2) {
121 			/*
122 			 * Ensure that for JMP8 the displacement
123 			 * actually fits the signed byte.
124 			 */
125 			BUG_ON((insn->disp >> 31) != (insn->disp >> 7));
126 		}
127 	}
128 }
129 
130 static __always_inline
text_gen_insn(u8 opcode,const void * addr,const void * dest)131 void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
132 {
133 	static union text_poke_insn insn; /* per instance */
134 	__text_gen_insn(&insn, opcode, addr, dest, text_opcode_size(opcode));
135 	return &insn.text;
136 }
137 
138 extern int after_bootmem;
139 extern __ro_after_init struct mm_struct *poking_mm;
140 extern __ro_after_init unsigned long poking_addr;
141 
142 #ifndef CONFIG_UML_X86
143 static __always_inline
int3_emulate_jmp(struct pt_regs * regs,unsigned long ip)144 void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
145 {
146 	regs->ip = ip;
147 }
148 
149 static __always_inline
int3_emulate_push(struct pt_regs * regs,unsigned long val)150 void int3_emulate_push(struct pt_regs *regs, unsigned long val)
151 {
152 	/*
153 	 * The int3 handler in entry_64.S adds a gap between the
154 	 * stack where the break point happened, and the saving of
155 	 * pt_regs. We can extend the original stack because of
156 	 * this gap. See the idtentry macro's create_gap option.
157 	 *
158 	 * Similarly entry_32.S will have a gap on the stack for (any) hardware
159 	 * exception and pt_regs; see FIXUP_FRAME.
160 	 */
161 	regs->sp -= sizeof(unsigned long);
162 	*(unsigned long *)regs->sp = val;
163 }
164 
165 static __always_inline
int3_emulate_pop(struct pt_regs * regs)166 unsigned long int3_emulate_pop(struct pt_regs *regs)
167 {
168 	unsigned long val = *(unsigned long *)regs->sp;
169 	regs->sp += sizeof(unsigned long);
170 	return val;
171 }
172 
173 static __always_inline
int3_emulate_call(struct pt_regs * regs,unsigned long func)174 void int3_emulate_call(struct pt_regs *regs, unsigned long func)
175 {
176 	int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
177 	int3_emulate_jmp(regs, func);
178 }
179 
180 static __always_inline
int3_emulate_ret(struct pt_regs * regs)181 void int3_emulate_ret(struct pt_regs *regs)
182 {
183 	unsigned long ip = int3_emulate_pop(regs);
184 	int3_emulate_jmp(regs, ip);
185 }
186 #endif /* !CONFIG_UML_X86 */
187 
188 #endif /* _ASM_X86_TEXT_PATCHING_H */
189