text-patching.h

  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/*
 10 * Currently, the max observed size in the kernel code is
 11 * JUMP_LABEL_NOP_SIZE/RELATIVEJUMP_SIZE, which are 5.
 12 * Raise it if needed.
 13 */
 14#define TEXT_POKE_MAX_OPCODE_SIZE	5
 15
 16extern void text_poke_early(void *addr, const void *opcode, size_t len);
 17
 18extern void text_poke_apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len);
 19
 20/*
 21 * Clear and restore the kernel write-protection flag on the local CPU.
 22 * Allows the kernel to edit read-only pages.
 23 * Side-effect: any interrupt handler running between save and restore will have
 24 * the ability to write to read-only pages.
 25 *
 26 * Warning:
 27 * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
 28 * no thread can be preempted in the instructions being modified (no iret to an
 29 * invalid instruction possible) or if the instructions are changed from a
 30 * consistent state to another consistent state atomically.
 31 * On the local CPU you need to be protected against NMI or MCE handlers seeing
 32 * an inconsistent instruction while you patch.
 33 */
 34extern void *text_poke(void *addr, const void *opcode, size_t len);
 35extern void smp_text_poke_sync_each_cpu(void);
 36extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
 37extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
 38#define text_poke_copy text_poke_copy
 39extern void *text_poke_copy_locked(void *addr, const void *opcode, size_t len, bool core_ok);
 40extern void *text_poke_set(void *addr, int c, size_t len);
 41extern int smp_text_poke_int3_handler(struct pt_regs *regs);
 42extern void smp_text_poke_single(void *addr, const void *opcode, size_t len, const void *emulate);
 43
 44extern void smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, const void *emulate);
 45extern void smp_text_poke_batch_finish(void);
 46
 47#define INT3_INSN_SIZE		1
 48#define INT3_INSN_OPCODE	0xCC
 49
 50#define RET_INSN_SIZE		1
 51#define RET_INSN_OPCODE		0xC3
 52
 53#define CALL_INSN_SIZE		5
 54#define CALL_INSN_OPCODE	0xE8
 55
 56#define JMP32_INSN_SIZE		5
 57#define JMP32_INSN_OPCODE	0xE9
 58
 59#define JMP8_INSN_SIZE		2
 60#define JMP8_INSN_OPCODE	0xEB
 61
 62#define DISP32_SIZE		4
 63
 64static __always_inline int text_opcode_size(u8 opcode)
 65{
 66	int size = 0;
 67
 68#define __CASE(insn)	\
 69	case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
 70
 71	switch(opcode) {
 72	__CASE(INT3);
 73	__CASE(RET);
 74	__CASE(CALL);
 75	__CASE(JMP32);
 76	__CASE(JMP8);
 77	}
 78
 79#undef __CASE
 80
 81	return size;
 82}
 83
 84union text_poke_insn {
 85	u8 text[TEXT_POKE_MAX_OPCODE_SIZE];
 86	struct {
 87		u8 opcode;
 88		s32 disp;
 89	} __attribute__((packed));
 90};
 91
 92static __always_inline
 93void __text_gen_insn(void *buf, u8 opcode, const void *addr, const void *dest, int size)
 94{
 95	union text_poke_insn *insn = buf;
 96
 97	BUG_ON(size < text_opcode_size(opcode));
 98
 99	/*
100	 * Hide the addresses to avoid the compiler folding in constants when
101	 * referencing code, these can mess up annotations like
102	 * ANNOTATE_NOENDBR.
103	 */
104	OPTIMIZER_HIDE_VAR(insn);
105	OPTIMIZER_HIDE_VAR(addr);
106	OPTIMIZER_HIDE_VAR(dest);
107
108	insn->opcode = opcode;
109
110	if (size > 1) {
111		insn->disp = (long)dest - (long)(addr + size);
112		if (size == 2) {
113			/*
114			 * Ensure that for JMP8 the displacement
115			 * actually fits the signed byte.
116			 */
117			BUG_ON((insn->disp >> 31) != (insn->disp >> 7));
118		}
119	}
120}
121
122static __always_inline
123void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
124{
125	static union text_poke_insn insn; /* per instance */
126	__text_gen_insn(&insn, opcode, addr, dest, text_opcode_size(opcode));
127	return &insn.text;
128}
129
130extern int after_bootmem;
131extern __ro_after_init struct mm_struct *text_poke_mm;
132extern __ro_after_init unsigned long text_poke_mm_addr;
133
134#ifndef CONFIG_UML_X86
135static __always_inline
136void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
137{
138	regs->ip = ip;
139}
140
141static __always_inline
142void int3_emulate_push(struct pt_regs *regs, unsigned long val)
143{
144	/*
145	 * The INT3 handler in entry_64.S adds a gap between the
146	 * stack where the break point happened, and the saving of
147	 * pt_regs. We can extend the original stack because of
148	 * this gap. See the idtentry macro's X86_TRAP_BP logic.
149	 *
150	 * Similarly, entry_32.S will have a gap on the stack for
151	 * (any) hardware exception and pt_regs; see the
152	 * FIXUP_FRAME macro.
153	 */
154	regs->sp -= sizeof(unsigned long);
155	*(unsigned long *)regs->sp = val;
156}
157
158static __always_inline
159unsigned long int3_emulate_pop(struct pt_regs *regs)
160{
161	unsigned long val = *(unsigned long *)regs->sp;
162	regs->sp += sizeof(unsigned long);
163	return val;
164}
165
166static __always_inline
167void int3_emulate_call(struct pt_regs *regs, unsigned long func)
168{
169	int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
170	int3_emulate_jmp(regs, func);
171}
172
173static __always_inline
174void int3_emulate_ret(struct pt_regs *regs)
175{
176	unsigned long ip = int3_emulate_pop(regs);
177	int3_emulate_jmp(regs, ip);
178}
179
180static __always_inline
181bool __emulate_cc(unsigned long flags, u8 cc)
182{
183	static const unsigned long cc_mask[6] = {
184		[0] = X86_EFLAGS_OF,
185		[1] = X86_EFLAGS_CF,
186		[2] = X86_EFLAGS_ZF,
187		[3] = X86_EFLAGS_CF | X86_EFLAGS_ZF,
188		[4] = X86_EFLAGS_SF,
189		[5] = X86_EFLAGS_PF,
190	};
191
192	bool invert = cc & 1;
193	bool match;
194
195	if (cc < 0xc) {
196		match = flags & cc_mask[cc >> 1];
197	} else {
198		match = ((flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^
199			((flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT);
200		if (cc >= 0xe)
201			match = match || (flags & X86_EFLAGS_ZF);
202	}
203
204	return (match && !invert) || (!match && invert);
205}
206
207static __always_inline
208void int3_emulate_jcc(struct pt_regs *regs, u8 cc, unsigned long ip, unsigned long disp)
209{
210	if (__emulate_cc(regs->flags, cc))
211		ip += disp;
212
213	int3_emulate_jmp(regs, ip);
214}
215
216#endif /* !CONFIG_UML_X86 */
217
218#endif /* _ASM_X86_TEXT_PATCHING_H */