include/asm/text-patching.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 #ifndef _ASM_X86_TEXT_PATCHING_H
0003 #define _ASM_X86_TEXT_PATCHING_H
0004
0005 #include <linux/types.h>
0006 #include <linux/stddef.h>
0007 #include <asm/ptrace.h>
0008
0009 struct paravirt_patch_site;
0010 #ifdef CONFIG_PARAVIRT
0011 void apply_paravirt(struct paravirt_patch_site *start,
0012             struct paravirt_patch_site *end);
0013 #else
0014 static inline void apply_paravirt(struct paravirt_patch_site *start,
0015                   struct paravirt_patch_site *end)
0016 {}
0017 #define __parainstructions  NULL
0018 #define __parainstructions_end  NULL
0019 #endif
0020
0021 /*
0022  * Currently, the max observed size in the kernel code is
0023  * JUMP_LABEL_NOP_SIZE/RELATIVEJUMP_SIZE, which are 5.
0024  * Raise it if needed.
0025  */
0026 #define POKE_MAX_OPCODE_SIZE    5
0027
0028 extern void text_poke_early(void *addr, const void *opcode, size_t len);
0029
0030 /*
0031  * Clear and restore the kernel write-protection flag on the local CPU.
0032  * Allows the kernel to edit read-only pages.
0033  * Side-effect: any interrupt handler running between save and restore will have
0034  * the ability to write to read-only pages.
0035  *
0036  * Warning:
0037  * Code patching in the UP case is safe if NMIs and MCE handlers are stopped and
0038  * no thread can be preempted in the instructions being modified (no iret to an
0039  * invalid instruction possible) or if the instructions are changed from a
0040  * consistent state to another consistent state atomically.
0041  * On the local CPU you need to be protected against NMI or MCE handlers seeing
0042  * an inconsistent instruction while you patch.
0043  */
0044 extern void *text_poke(void *addr, const void *opcode, size_t len);
0045 extern void text_poke_sync(void);
0046 extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len);
0047 extern void *text_poke_copy(void *addr, const void *opcode, size_t len);
0048 extern void *text_poke_set(void *addr, int c, size_t len);
0049 extern int poke_int3_handler(struct pt_regs *regs);
0050 extern void text_poke_bp(void *addr, const void *opcode, size_t len, const void *emulate);
0051
0052 extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate);
0053 extern void text_poke_finish(void);
0054
0055 #define INT3_INSN_SIZE      1
0056 #define INT3_INSN_OPCODE    0xCC
0057
0058 #define RET_INSN_SIZE       1
0059 #define RET_INSN_OPCODE     0xC3
0060
0061 #define CALL_INSN_SIZE      5
0062 #define CALL_INSN_OPCODE    0xE8
0063
0064 #define JMP32_INSN_SIZE     5
0065 #define JMP32_INSN_OPCODE   0xE9
0066
0067 #define JMP8_INSN_SIZE      2
0068 #define JMP8_INSN_OPCODE    0xEB
0069
0070 #define DISP32_SIZE     4
0071
0072 static __always_inline int text_opcode_size(u8 opcode)
0073 {
0074     int size = 0;
0075
0076 #define __CASE(insn)    \
0077     case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break
0078
0079     switch(opcode) {
0080     __CASE(INT3);
0081     __CASE(RET);
0082     __CASE(CALL);
0083     __CASE(JMP32);
0084     __CASE(JMP8);
0085     }
0086
0087 #undef __CASE
0088
0089     return size;
0090 }
0091
0092 union text_poke_insn {
0093     u8 text[POKE_MAX_OPCODE_SIZE];
0094     struct {
0095         u8 opcode;
0096         s32 disp;
0097     } __attribute__((packed));
0098 };
0099
0100 static __always_inline
0101 void __text_gen_insn(void *buf, u8 opcode, const void *addr, const void *dest, int size)
0102 {
0103     union text_poke_insn *insn = buf;
0104
0105     BUG_ON(size < text_opcode_size(opcode));
0106
0107     /*
0108      * Hide the addresses to avoid the compiler folding in constants when
0109      * referencing code, these can mess up annotations like
0110      * ANNOTATE_NOENDBR.
0111      */
0112     OPTIMIZER_HIDE_VAR(insn);
0113     OPTIMIZER_HIDE_VAR(addr);
0114     OPTIMIZER_HIDE_VAR(dest);
0115
0116     insn->opcode = opcode;
0117
0118     if (size > 1) {
0119         insn->disp = (long)dest - (long)(addr + size);
0120         if (size == 2) {
0121             /*
0122              * Ensure that for JMP8 the displacement
0123              * actually fits the signed byte.
0124              */
0125             BUG_ON((insn->disp >> 31) != (insn->disp >> 7));
0126         }
0127     }
0128 }
0129
0130 static __always_inline
0131 void *text_gen_insn(u8 opcode, const void *addr, const void *dest)
0132 {
0133     static union text_poke_insn insn; /* per instance */
0134     __text_gen_insn(&insn, opcode, addr, dest, text_opcode_size(opcode));
0135     return &insn.text;
0136 }
0137
0138 extern int after_bootmem;
0139 extern __ro_after_init struct mm_struct *poking_mm;
0140 extern __ro_after_init unsigned long poking_addr;
0141
0142 #ifndef CONFIG_UML_X86
0143 static __always_inline
0144 void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip)
0145 {
0146     regs->ip = ip;
0147 }
0148
0149 static __always_inline
0150 void int3_emulate_push(struct pt_regs *regs, unsigned long val)
0151 {
0152     /*
0153      * The int3 handler in entry_64.S adds a gap between the
0154      * stack where the break point happened, and the saving of
0155      * pt_regs. We can extend the original stack because of
0156      * this gap. See the idtentry macro's create_gap option.
0157      *
0158      * Similarly entry_32.S will have a gap on the stack for (any) hardware
0159      * exception and pt_regs; see FIXUP_FRAME.
0160      */
0161     regs->sp -= sizeof(unsigned long);
0162     *(unsigned long *)regs->sp = val;
0163 }
0164
0165 static __always_inline
0166 unsigned long int3_emulate_pop(struct pt_regs *regs)
0167 {
0168     unsigned long val = *(unsigned long *)regs->sp;
0169     regs->sp += sizeof(unsigned long);
0170     return val;
0171 }
0172
0173 static __always_inline
0174 void int3_emulate_call(struct pt_regs *regs, unsigned long func)
0175 {
0176     int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + CALL_INSN_SIZE);
0177     int3_emulate_jmp(regs, func);
0178 }
0179
0180 static __always_inline
0181 void int3_emulate_ret(struct pt_regs *regs)
0182 {
0183     unsigned long ip = int3_emulate_pop(regs);
0184     int3_emulate_jmp(regs, ip);
0185 }
0186 #endif /* !CONFIG_UML_X86 */
0187
0188 #endif /* _ASM_X86_TEXT_PATCHING_H */