Messages in this thread Patch in this message | | | Date | Thu, 3 Oct 2019 15:05:09 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH 1/3] x86/alternatives: Teach text_poke_bp() to emulate instructions |
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On Thu, Oct 03, 2019 at 10:27:51AM +0200, Peter Zijlstra wrote: > On Thu, Oct 03, 2019 at 02:00:50PM +0900, Masami Hiramatsu wrote: > > > > This fits almost all text_poke_bp() users, except > > > arch_unoptimize_kprobe() which restores random text, and for that site > > > we have to build an explicit emulate instruction. > > > > OK, and in this case, I would like to change RELATIVEJUMP_OPCODE > > to JMP32_INSN_OPCODE for readability. (or at least > > making RELATIVEJUMP_OPCODE as an alias of JMP32_INSN_OPCODE) > > > > @@ -448,12 +447,18 @@ void arch_optimize_kprobes(struct list_h > > > void arch_unoptimize_kprobe(struct optimized_kprobe *op) > > > { > > > u8 insn_buff[RELATIVEJUMP_SIZE]; > > > + u8 emulate_buff[RELATIVEJUMP_SIZE]; > > > > > > /* Set int3 to first byte for kprobes */ > > > insn_buff[0] = BREAKPOINT_INSTRUCTION; > > > memcpy(insn_buff + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE); > > > + > > > + emulate_buff[0] = RELATIVEJUMP_OPCODE; > > > + *(s32 *)(&emulate_buff[1]) = (s32)((long)op->optinsn.insn - > > > + ((long)op->kp.addr + RELATIVEJUMP_SIZE)); > > I'm halfway through a patch introducing: > > union text_poke_insn { > u8 code[POKE_MAX_OPCODE_SUZE]; > struct { > u8 opcode; > s32 disp; > } __attribute__((packed)); > }; > > to text-patching.h to unify all such custom unions we have all over the > place. I'll mob up the above in that.
How's something like so?
--- a/arch/x86/include/asm/text-patching.h +++ b/arch/x86/include/asm/text-patching.h @@ -49,6 +49,8 @@ extern void text_poke_bp(void *addr, con extern void text_poke_queue(void *addr, const void *opcode, size_t len, const void *emulate); extern void text_poke_finish(void); +extern void *text_gen_insn(u8 opcode, unsigned long addr, unsigned long dest); + extern int after_bootmem; extern __ro_after_init struct mm_struct *poking_mm; extern __ro_after_init unsigned long poking_addr; --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1237,3 +1237,39 @@ void text_poke_bp(void *addr, const void text_poke_loc_init(&tp, addr, opcode, len, emulate); text_poke_bp_batch(&tp, 1); } + +union text_poke_insn { + u8 text[POKE_MAX_OPCODE_SIZE]; + struct { + u8 opcode; + s32 disp; + } __attribute__((packed)); +}; + +void *text_gen_insn(u8 opcode, unsigned long addr, unsigned long dest) +{ + static union text_poke_insn insn; /* text_mutex */ + int size = 0; + + lockdep_assert_held(&text_mutex); + + insn.opcode = opcode; + +#define __CASE(insn) \ + case insn##_INSN_OPCODE: size = insn##_INSN_SIZE; break + + switch(opcode) { + __CASE(INT3); + __CASE(CALL); + __CASE(JMP32); + __CASE(JMP8); + } + + if (size > 1) { + insn.disp = dest - (addr + size); + if (size == 2) + BUG_ON((insn.disp >> 31) != (insn.disp >> 7)); + } + + return &insn.text; +} --- a/arch/x86/kernel/jump_label.c +++ b/arch/x86/kernel/jump_label.c @@ -16,14 +16,6 @@ #include <asm/alternative.h> #include <asm/text-patching.h> -union jump_code_union { - char code[JUMP_LABEL_NOP_SIZE]; - struct { - char jump; - int offset; - } __attribute__((packed)); -}; - static void bug_at(unsigned char *ip, int line) { /* @@ -38,33 +30,29 @@ static void bug_at(unsigned char *ip, in static const void * __jump_label_set_jump_code(struct jump_entry *entry, enum jump_label_type type, int init) { - static union jump_code_union code; /* relies on text_mutex */ const unsigned char default_nop[] = { STATIC_KEY_INIT_NOP }; const unsigned char *ideal_nop = ideal_nops[NOP_ATOMIC5]; - const void *expect; + const void *expect, *code; int line; - lockdep_assert_held(&text_mutex); - - code.jump = JMP32_INSN_OPCODE; - code.offset = jump_entry_target(entry) - - (jump_entry_code(entry) + JUMP_LABEL_NOP_SIZE); + code = text_gen_insn(JMP32_INSN_OPCODE, jump_entry_code(entry), + jump_entry_target(entry)); if (init) { expect = default_nop; line = __LINE__; } else if (type == JUMP_LABEL_JMP) { expect = ideal_nop; line = __LINE__; } else { - expect = code.code; line = __LINE__; + expect = code; line = __LINE__; } if (memcmp((void *)jump_entry_code(entry), expect, JUMP_LABEL_NOP_SIZE)) bug_at((void *)jump_entry_code(entry), line); if (type == JUMP_LABEL_NOP) - memcpy(&code, ideal_nop, JUMP_LABEL_NOP_SIZE); + code = ideal_nop; - return &code; + return code; } static void inline __jump_label_transform(struct jump_entry *entry, --- a/arch/x86/kernel/kprobes/opt.c +++ b/arch/x86/kernel/kprobes/opt.c @@ -447,18 +447,13 @@ void arch_optimize_kprobes(struct list_h void arch_unoptimize_kprobe(struct optimized_kprobe *op) { u8 insn_buff[RELATIVEJUMP_SIZE]; - u8 emulate_buff[RELATIVEJUMP_SIZE]; /* Set int3 to first byte for kprobes */ insn_buff[0] = BREAKPOINT_INSTRUCTION; memcpy(insn_buff + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE); - emulate_buff[0] = RELATIVEJUMP_OPCODE; - *(s32 *)(&emulate_buff[1]) = (s32)((long)op->optinsn.insn - - ((long)op->kp.addr + RELATIVEJUMP_SIZE)); - text_poke_bp(op->kp.addr, insn_buff, RELATIVEJUMP_SIZE, - emulate_buff); + text_gen_insn(JMP32_INSN_OPCODE, (long)op->kp.addr, (long)op->optinsn.insn)); } /*
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