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 16 extern void text_poke_early(void *addr, const void *opcode, size_t len); 17 18 extern 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 */ 34 extern void *text_poke(void *addr, const void *opcode, size_t len); 35 extern void smp_text_poke_sync_each_cpu(void); 36 extern void *text_poke_kgdb(void *addr, const void *opcode, size_t len); 37 extern void *text_poke_copy(void *addr, const void *opcode, size_t len); 38 #define text_poke_copy text_poke_copy 39 extern void *text_poke_copy_locked(void *addr, const void *opcode, size_t len, bool core_ok); 40 extern void *text_poke_set(void *addr, int c, size_t len); 41 extern int smp_text_poke_int3_handler(struct pt_regs *regs); 42 extern void smp_text_poke_single(void *addr, const void *opcode, size_t len, const void *emulate); 43 44 extern void smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, const void *emulate); 45 extern 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 64 static __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 84 union text_poke_insn { 85 u8 text[TEXT_POKE_MAX_OPCODE_SIZE]; 86 struct { 87 u8 opcode; 88 s32 disp; 89 } __attribute__((packed)); 90 }; 91 92 static __always_inline 93 void __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 } 121 122 static __always_inline 123 void *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 } 129 130 extern int after_bootmem; 131 extern __ro_after_init struct mm_struct *text_poke_mm; 132 extern __ro_after_init unsigned long text_poke_mm_addr; 133 134 #ifndef CONFIG_UML_X86 135 static __always_inline 136 void int3_emulate_jmp(struct pt_regs *regs, unsigned long ip) 137 { 138 regs->ip = ip; 139 } 140 141 static __always_inline 142 void 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 } 157 158 static __always_inline 159 unsigned 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 } 165 166 static __always_inline 167 void 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 } 172 173 static __always_inline 174 void int3_emulate_ret(struct pt_regs *regs) 175 { 176 unsigned long ip = int3_emulate_pop(regs); 177 int3_emulate_jmp(regs, ip); 178 } 179 180 static __always_inline 181 void int3_emulate_jcc(struct pt_regs *regs, u8 cc, unsigned long ip, unsigned long disp) 182 { 183 static const unsigned long jcc_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 = regs->flags & jcc_mask[cc >> 1]; 197 } else { 198 match = ((regs->flags & X86_EFLAGS_SF) >> X86_EFLAGS_SF_BIT) ^ 199 ((regs->flags & X86_EFLAGS_OF) >> X86_EFLAGS_OF_BIT); 200 if (cc >= 0xe) 201 match = match || (regs->flags & X86_EFLAGS_ZF); 202 } 203 204 if ((match && !invert) || (!match && invert)) 205 ip += disp; 206 207 int3_emulate_jmp(regs, ip); 208 } 209 210 #endif /* !CONFIG_UML_X86 */ 211 212 #endif /* _ASM_X86_TEXT_PATCHING_H */ 213