xref: /linux/arch/x86/kernel/kprobes/core.c (revision 148ab873d8194cb44f29474da3b4428fa2e100d1)

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 *  Kernel Probes (KProbes)
 *
 * Copyright (C) IBM Corporation, 2002, 2004
 *
 * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
 *		Probes initial implementation ( includes contributions from
 *		Rusty Russell).
 * 2004-July	Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
 *		interface to access function arguments.
 * 2004-Oct	Jim Keniston <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *		<prasanna@in.ibm.com> adapted for x86_64 from i386.
 * 2005-Mar	Roland McGrath <roland@redhat.com>
 *		Fixed to handle %rip-relative addressing mode correctly.
 * 2005-May	Hien Nguyen <hien@us.ibm.com>, Jim Keniston
 *		<jkenisto@us.ibm.com> and Prasanna S Panchamukhi
 *		<prasanna@in.ibm.com> added function-return probes.
 * 2005-May	Rusty Lynch <rusty.lynch@intel.com>
 *		Added function return probes functionality
 * 2006-Feb	Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp> added
 *		kprobe-booster and kretprobe-booster for i386.
 * 2007-Dec	Masami Hiramatsu <mhiramat@redhat.com> added kprobe-booster
 *		and kretprobe-booster for x86-64
 * 2007-Dec	Masami Hiramatsu <mhiramat@redhat.com>, Arjan van de Ven
 *		<arjan@infradead.org> and Jim Keniston <jkenisto@us.ibm.com>
 *		unified x86 kprobes code.
 */
#include <linux/kprobes.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
#include <linux/preempt.h>
#include <linux/sched/debug.h>
#include <linux/perf_event.h>
#include <linux/extable.h>
#include <linux/kdebug.h>
#include <linux/kallsyms.h>
#include <linux/kgdb.h>
#include <linux/ftrace.h>
#include <linux/kasan.h>
#include <linux/objtool.h>
#include <linux/vmalloc.h>
#include <linux/pgtable.h>
#include <linux/set_memory.h>
#include <linux/cfi.h>
#include <linux/execmem.h>

#include <asm/text-patching.h>
#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <linux/uaccess.h>
#include <asm/alternative.h>
#include <asm/insn.h>
#include <asm/debugreg.h>
#include <asm/ibt.h>

#include "common.h"

DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);

#define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\
	(((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) |   \
	  (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) |   \
	  (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) |   \
	  (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf))    \
	 << (row % 32))
	/*
	 * Undefined/reserved opcodes, conditional jump, Opcode Extension
	 * Groups, and some special opcodes can not boost.
	 * This is non-const and volatile to keep gcc from statically
	 * optimizing it out, as variable_test_bit makes gcc think only
	 * *(unsigned long*) is used.
	 */
static volatile u32 twobyte_is_boostable[256 / 32] = {
	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f          */
	/*      ----------------------------------------------          */
	W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */
	W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1) , /* 10 */
	W(0x20, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 20 */
	W(0x30, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 30 */
	W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
	W(0x50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 50 */
	W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1) | /* 60 */
	W(0x70, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1) , /* 70 */
	W(0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 80 */
	W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
	W(0xa0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* a0 */
	W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1) , /* b0 */
	W(0xc0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* c0 */
	W(0xd0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) , /* d0 */
	W(0xe0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* e0 */
	W(0xf0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0)   /* f0 */
	/*      -----------------------------------------------         */
	/*      0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f          */
};
#undef W

struct kretprobe_blackpoint kretprobe_blacklist[] = {
	{"__switch_to", }, /* This function switches only current task, but
			      doesn't switch kernel stack.*/
	{NULL, NULL}	/* Terminator */
};

const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist);

static nokprobe_inline void
__synthesize_relative_insn(void *dest, void *from, void *to, u8 op)
{
	struct __arch_relative_insn {
		u8 op;
		s32 raddr;
	} __packed *insn;

	insn = (struct __arch_relative_insn *)dest;
	insn->raddr = (s32)((long)(to) - ((long)(from) + 5));
	insn->op = op;
}

/* Insert a jump instruction at address 'from', which jumps to address 'to'.*/
void synthesize_reljump(void *dest, void *from, void *to)
{
	__synthesize_relative_insn(dest, from, to, JMP32_INSN_OPCODE);
}
NOKPROBE_SYMBOL(synthesize_reljump);

/* Insert a call instruction at address 'from', which calls address 'to'.*/
void synthesize_relcall(void *dest, void *from, void *to)
{
	__synthesize_relative_insn(dest, from, to, CALL_INSN_OPCODE);
}
NOKPROBE_SYMBOL(synthesize_relcall);

/*
 * Returns non-zero if INSN is boostable.
 * RIP relative instructions are adjusted at copying time in 64 bits mode
 */
bool can_boost(struct insn *insn, void *addr)
{
	kprobe_opcode_t opcode;
	insn_byte_t prefix;

	if (search_exception_tables((unsigned long)addr))
		return false;	/* Page fault may occur on this address. */

	/* 2nd-byte opcode */
	if (insn->opcode.nbytes == 2)
		return test_bit(insn->opcode.bytes[1],
				(unsigned long *)twobyte_is_boostable);

	if (insn->opcode.nbytes != 1)
		return false;

	for_each_insn_prefix(insn, prefix) {
		insn_attr_t attr;

		attr = inat_get_opcode_attribute(prefix);
		/* Can't boost Address-size override prefix and CS override prefix */
		if (prefix == 0x2e || inat_is_address_size_prefix(attr))
			return false;
	}

	opcode = insn->opcode.bytes[0];

	switch (opcode) {
	case 0x62:		/* bound */
	case 0x70 ... 0x7f:	/* Conditional jumps */
	case 0x9a:		/* Call far */
	case 0xcc ... 0xce:	/* software exceptions */
	case 0xd6:		/* (UD) */
	case 0xd8 ... 0xdf:	/* ESC */
	case 0xe0 ... 0xe3:	/* LOOP*, JCXZ */
	case 0xe8 ... 0xe9:	/* near Call, JMP */
	case 0xeb:		/* Short JMP */
	case 0xf0 ... 0xf4:	/* LOCK/REP, HLT */
		/* ... are not boostable */
		return false;
	case 0xc0 ... 0xc1:	/* Grp2 */
	case 0xd0 ... 0xd3:	/* Grp2 */
		/*
		 * AMD uses nnn == 110 as SHL/SAL, but Intel makes it reserved.
		 */
		return X86_MODRM_REG(insn->modrm.bytes[0]) != 0b110;
	case 0xf6 ... 0xf7:	/* Grp3 */
		/* AMD uses nnn == 001 as TEST, but Intel makes it reserved. */
		return X86_MODRM_REG(insn->modrm.bytes[0]) != 0b001;
	case 0xfe:		/* Grp4 */
		/* Only INC and DEC are boostable */
		return X86_MODRM_REG(insn->modrm.bytes[0]) == 0b000 ||
		       X86_MODRM_REG(insn->modrm.bytes[0]) == 0b001;
	case 0xff:		/* Grp5 */
		/* Only INC, DEC, and indirect JMP are boostable */
		return X86_MODRM_REG(insn->modrm.bytes[0]) == 0b000 ||
		       X86_MODRM_REG(insn->modrm.bytes[0]) == 0b001 ||
		       X86_MODRM_REG(insn->modrm.bytes[0]) == 0b100;
	default:
		return true;
	}
}

static unsigned long
__recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
{
	struct kprobe *kp;
	bool faddr;

	kp = get_kprobe((void *)addr);
	faddr = ftrace_location(addr) == addr;
	/*
	 * Use the current code if it is not modified by Kprobe
	 * and it cannot be modified by ftrace.
	 */
	if (!kp && !faddr)
		return addr;

	/*
	 * Basically, kp->ainsn.insn has an original instruction.
	 * However, RIP-relative instruction can not do single-stepping
	 * at different place, __copy_instruction() tweaks the displacement of
	 * that instruction. In that case, we can't recover the instruction
	 * from the kp->ainsn.insn.
	 *
	 * On the other hand, in case on normal Kprobe, kp->opcode has a copy
	 * of the first byte of the probed instruction, which is overwritten
	 * by int3. And the instruction at kp->addr is not modified by kprobes
	 * except for the first byte, we can recover the original instruction
	 * from it and kp->opcode.
	 *
	 * In case of Kprobes using ftrace, we do not have a copy of
	 * the original instruction. In fact, the ftrace location might
	 * be modified at anytime and even could be in an inconsistent state.
	 * Fortunately, we know that the original code is the ideal 5-byte
	 * long NOP.
	 */
	if (copy_from_kernel_nofault(buf, (void *)addr,
		MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
		return 0UL;

	if (faddr)
		memcpy(buf, x86_nops[5], 5);
	else
		buf[0] = kp->opcode;
	return (unsigned long)buf;
}

/*
 * Recover the probed instruction at addr for further analysis.
 * Caller must lock kprobes by kprobe_mutex, or disable preemption
 * for preventing to release referencing kprobes.
 * Returns zero if the instruction can not get recovered (or access failed).
 */
unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
{
	unsigned long __addr;

	__addr = __recover_optprobed_insn(buf, addr);
	if (__addr != addr)
		return __addr;

	return __recover_probed_insn(buf, addr);
}

/* Check if insn is INT or UD */
static inline bool is_exception_insn(struct insn *insn)
{
	/* UD uses 0f escape */
	if (insn->opcode.bytes[0] == 0x0f) {
		/* UD0 / UD1 / UD2 */
		return insn->opcode.bytes[1] == 0xff ||
		       insn->opcode.bytes[1] == 0xb9 ||
		       insn->opcode.bytes[1] == 0x0b;
	}

	/* INT3 / INT n / INTO / INT1 */
	return insn->opcode.bytes[0] == 0xcc ||
	       insn->opcode.bytes[0] == 0xcd ||
	       insn->opcode.bytes[0] == 0xce ||
	       insn->opcode.bytes[0] == 0xf1;
}

/*
 * Check if paddr is at an instruction boundary and that instruction can
 * be probed
 */
static bool can_probe(unsigned long paddr)
{
	unsigned long addr, __addr, offset = 0;
	struct insn insn;
	kprobe_opcode_t buf[MAX_INSN_SIZE];

	if (!kallsyms_lookup_size_offset(paddr, NULL, &offset))
		return false;

	/* Decode instructions */
	addr = paddr - offset;
	while (addr < paddr) {
		/*
		 * Check if the instruction has been modified by another
		 * kprobe, in which case we replace the breakpoint by the
		 * original instruction in our buffer.
		 * Also, jump optimization will change the breakpoint to
		 * relative-jump. Since the relative-jump itself is
		 * normally used, we just go through if there is no kprobe.
		 */
		__addr = recover_probed_instruction(buf, addr);
		if (!__addr)
			return false;

		if (insn_decode_kernel(&insn, (void *)__addr) < 0)
			return false;

#ifdef CONFIG_KGDB
		/*
		 * If there is a dynamically installed kgdb sw breakpoint,
		 * this function should not be probed.
		 */
		if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
		    kgdb_has_hit_break(addr))
			return false;
#endif
		addr += insn.length;
	}

	/* Check if paddr is at an instruction boundary */
	if (addr != paddr)
		return false;

	__addr = recover_probed_instruction(buf, addr);
	if (!__addr)
		return false;

	if (insn_decode_kernel(&insn, (void *)__addr) < 0)
		return false;

	/* INT and UD are special and should not be kprobed */
	if (is_exception_insn(&insn))
		return false;

	if (IS_ENABLED(CONFIG_CFI)) {
		/*
		 * The compiler generates the following instruction sequence
		 * for indirect call checks and cfi.c decodes this;
		 *
		 *   movl    -<id>, %r10d       ; 6 bytes
		 *   addl    -4(%reg), %r10d    ; 4 bytes
		 *   je      .Ltmp1             ; 2 bytes
		 *   ud2                        ; <- regs->ip
		 *   .Ltmp1:
		 *
		 * Also, these movl and addl are used for showing expected
		 * type. So those must not be touched.
		 */
		if (insn.opcode.value == 0xBA)
			offset = 12;
		else if (insn.opcode.value == 0x3)
			offset = 6;
		else
			goto out;

		/* This movl/addl is used for decoding CFI. */
		if (is_cfi_trap(addr + offset))
			return false;
	}

out:
	return true;
}

/* If x86 supports IBT (ENDBR) it must be skipped. */
kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
					 bool *on_func_entry)
{
	if (is_endbr((u32 *)addr)) {
		*on_func_entry = !offset || offset == 4;
		if (*on_func_entry)
			offset = 4;

	} else {
		*on_func_entry = !offset;
	}

	return (kprobe_opcode_t *)(addr + offset);
}

/*
 * Copy an instruction with recovering modified instruction by kprobes
 * and adjust the displacement if the instruction uses the %rip-relative
 * addressing mode. Note that since @real will be the final place of copied
 * instruction, displacement must be adjust by @real, not @dest.
 * This returns the length of copied instruction, or 0 if it has an error.
 */
int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
{
	kprobe_opcode_t buf[MAX_INSN_SIZE];
	unsigned long recovered_insn = recover_probed_instruction(buf, (unsigned long)src);
	int ret;

	if (!recovered_insn || !insn)
		return 0;

	/* This can access kernel text if given address is not recovered */
	if (copy_from_kernel_nofault(dest, (void *)recovered_insn,
			MAX_INSN_SIZE))
		return 0;

	ret = insn_decode_kernel(insn, dest);
	if (ret < 0)
		return 0;

	/* We can not probe force emulate prefixed instruction */
	if (insn_has_emulate_prefix(insn))
		return 0;

	/* Another subsystem puts a breakpoint, failed to recover */
	if (insn->opcode.bytes[0] == INT3_INSN_OPCODE)
		return 0;

	/* We should not singlestep on the exception masking instructions */
	if (insn_masking_exception(insn))
		return 0;

#ifdef CONFIG_X86_64
	/* Only x86_64 has RIP relative instructions */
	if (insn_rip_relative(insn)) {
		s64 newdisp;
		u8 *disp;
		/*
		 * The copied instruction uses the %rip-relative addressing
		 * mode.  Adjust the displacement for the difference between
		 * the original location of this instruction and the location
		 * of the copy that will actually be run.  The tricky bit here
		 * is making sure that the sign extension happens correctly in
		 * this calculation, since we need a signed 32-bit result to
		 * be sign-extended to 64 bits when it's added to the %rip
		 * value and yield the same 64-bit result that the sign-
		 * extension of the original signed 32-bit displacement would
		 * have given.
		 */
		newdisp = (u8 *) src + (s64) insn->displacement.value
			  - (u8 *) real;
		if ((s64) (s32) newdisp != newdisp) {
			pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp);
			return 0;
		}
		disp = (u8 *) dest + insn_offset_displacement(insn);
		*(s32 *) disp = (s32) newdisp;
	}
#endif
	return insn->length;
}

/* Prepare reljump or int3 right after instruction */
static int prepare_singlestep(kprobe_opcode_t *buf, struct kprobe *p,
			      struct insn *insn)
{
	int len = insn->length;

	if (!IS_ENABLED(CONFIG_PREEMPTION) &&
	    !p->post_handler && can_boost(insn, p->addr) &&
	    MAX_INSN_SIZE - len >= JMP32_INSN_SIZE) {
		/*
		 * These instructions can be executed directly if it
		 * jumps back to correct address.
		 */
		synthesize_reljump(buf + len, p->ainsn.insn + len,
				   p->addr + insn->length);
		len += JMP32_INSN_SIZE;
		p->ainsn.boostable = 1;
	} else {
		/* Otherwise, put an int3 for trapping singlestep */
		if (MAX_INSN_SIZE - len < INT3_INSN_SIZE)
			return -ENOSPC;

		buf[len] = INT3_INSN_OPCODE;
		len += INT3_INSN_SIZE;
	}

	return len;
}

/* Kprobe x86 instruction emulation - only regs->ip or IF flag modifiers */

static void kprobe_emulate_ifmodifiers(struct kprobe *p, struct pt_regs *regs)
{
	switch (p->ainsn.opcode) {
	case 0xfa:	/* cli */
		regs->flags &= ~(X86_EFLAGS_IF);
		break;
	case 0xfb:	/* sti */
		regs->flags |= X86_EFLAGS_IF;
		break;
	case 0x9c:	/* pushf */
		int3_emulate_push(regs, regs->flags);
		break;
	case 0x9d:	/* popf */
		regs->flags = int3_emulate_pop(regs);
		break;
	}
	regs->ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
}
NOKPROBE_SYMBOL(kprobe_emulate_ifmodifiers);

static void kprobe_emulate_ret(struct kprobe *p, struct pt_regs *regs)
{
	int3_emulate_ret(regs);
}
NOKPROBE_SYMBOL(kprobe_emulate_ret);

static void kprobe_emulate_call(struct kprobe *p, struct pt_regs *regs)
{
	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;

	int3_emulate_call(regs, ip, ip + p->ainsn.rel32);
}
NOKPROBE_SYMBOL(kprobe_emulate_call);

static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
{
	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;

	ip += p->ainsn.rel32;
	int3_emulate_jmp(regs, ip);
}
NOKPROBE_SYMBOL(kprobe_emulate_jmp);

static void kprobe_emulate_jcc(struct kprobe *p, struct pt_regs *regs)
{
	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;

	int3_emulate_jcc(regs, p->ainsn.jcc.type, ip, p->ainsn.rel32);
}
NOKPROBE_SYMBOL(kprobe_emulate_jcc);

static void kprobe_emulate_loop(struct kprobe *p, struct pt_regs *regs)
{
	unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
	bool match;

	if (p->ainsn.loop.type != 3) {	/* LOOP* */
		if (p->ainsn.loop.asize == 32)
			match = ((*(u32 *)&regs->cx)--) != 0;
#ifdef CONFIG_X86_64
		else if (p->ainsn.loop.asize == 64)
			match = ((*(u64 *)&regs->cx)--) != 0;
#endif
		else
			match = ((*(u16 *)&regs->cx)--) != 0;
	} else {			/* JCXZ */
		if (p->ainsn.loop.asize == 32)
			match = *(u32 *)(&regs->cx) == 0;
#ifdef CONFIG_X86_64
		else if (p->ainsn.loop.asize == 64)
			match = *(u64 *)(&regs->cx) == 0;
#endif
		else
			match = *(u16 *)(&regs->cx) == 0;
	}

	if (p->ainsn.loop.type == 0)	/* LOOPNE */
		match = match && !(regs->flags & X86_EFLAGS_ZF);
	else if (p->ainsn.loop.type == 1)	/* LOOPE */
		match = match && (regs->flags & X86_EFLAGS_ZF);

	if (match)
		ip += p->ainsn.rel32;
	int3_emulate_jmp(regs, ip);
}
NOKPROBE_SYMBOL(kprobe_emulate_loop);

static const int addrmode_regoffs[] = {
	offsetof(struct pt_regs, ax),
	offsetof(struct pt_regs, cx),
	offsetof(struct pt_regs, dx),
	offsetof(struct pt_regs, bx),
	offsetof(struct pt_regs, sp),
	offsetof(struct pt_regs, bp),
	offsetof(struct pt_regs, si),
	offsetof(struct pt_regs, di),
#ifdef CONFIG_X86_64
	offsetof(struct pt_regs, r8),
	offsetof(struct pt_regs, r9),
	offsetof(struct pt_regs, r10),
	offsetof(struct pt_regs, r11),
	offsetof(struct pt_regs, r12),
	offsetof(struct pt_regs, r13),
	offsetof(struct pt_regs, r14),
	offsetof(struct pt_regs, r15),
#endif
};

static void kprobe_emulate_call_indirect(struct kprobe *p, struct pt_regs *regs)
{
	unsigned long offs = addrmode_regoffs[p->ainsn.indirect.reg];

	int3_emulate_push(regs, regs->ip - INT3_INSN_SIZE + p->ainsn.size);
	int3_emulate_jmp(regs, regs_get_register(regs, offs));
}
NOKPROBE_SYMBOL(kprobe_emulate_call_indirect);

static void kprobe_emulate_jmp_indirect(struct kprobe *p, struct pt_regs *regs)
{
	unsigned long offs = addrmode_regoffs[p->ainsn.indirect.reg];

	int3_emulate_jmp(regs, regs_get_register(regs, offs));
}
NOKPROBE_SYMBOL(kprobe_emulate_jmp_indirect);

static int prepare_emulation(struct kprobe *p, struct insn *insn)
{
	insn_byte_t opcode = insn->opcode.bytes[0];

	switch (opcode) {
	case 0xfa:		/* cli */
	case 0xfb:		/* sti */
	case 0x9c:		/* pushfl */
	case 0x9d:		/* popf/popfd */
		/*
		 * IF modifiers must be emulated since it will enable interrupt while
		 * int3 single stepping.
		 */
		p->ainsn.emulate_op = kprobe_emulate_ifmodifiers;
		p->ainsn.opcode = opcode;
		break;
	case 0xc2:	/* ret/lret */
	case 0xc3:
	case 0xca:
	case 0xcb:
		p->ainsn.emulate_op = kprobe_emulate_ret;
		break;
	case 0x9a:	/* far call absolute -- segment is not supported */
	case 0xea:	/* far jmp absolute -- segment is not supported */
	case 0xcc:	/* int3 */
	case 0xcf:	/* iret -- in-kernel IRET is not supported */
		return -EOPNOTSUPP;
		break;
	case 0xe8:	/* near call relative */
		p->ainsn.emulate_op = kprobe_emulate_call;
		if (insn->immediate.nbytes == 2)
			p->ainsn.rel32 = *(s16 *)&insn->immediate.value;
		else
			p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
		break;
	case 0xeb:	/* short jump relative */
	case 0xe9:	/* near jump relative */
		p->ainsn.emulate_op = kprobe_emulate_jmp;
		if (insn->immediate.nbytes == 1)
			p->ainsn.rel32 = *(s8 *)&insn->immediate.value;
		else if (insn->immediate.nbytes == 2)
			p->ainsn.rel32 = *(s16 *)&insn->immediate.value;
		else
			p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
		break;
	case 0x70 ... 0x7f:
		/* 1 byte conditional jump */
		p->ainsn.emulate_op = kprobe_emulate_jcc;
		p->ainsn.jcc.type = opcode & 0xf;
		p->ainsn.rel32 = insn->immediate.value;
		break;
	case 0x0f:
		opcode = insn->opcode.bytes[1];
		if ((opcode & 0xf0) == 0x80) {
			/* 2 bytes Conditional Jump */
			p->ainsn.emulate_op = kprobe_emulate_jcc;
			p->ainsn.jcc.type = opcode & 0xf;
			if (insn->immediate.nbytes == 2)
				p->ainsn.rel32 = *(s16 *)&insn->immediate.value;
			else
				p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
		} else if (opcode == 0x01 &&
			   X86_MODRM_REG(insn->modrm.bytes[0]) == 0 &&
			   X86_MODRM_MOD(insn->modrm.bytes[0]) == 3) {
			/* VM extensions - not supported */
			return -EOPNOTSUPP;
		}
		break;
	case 0xe0:	/* Loop NZ */
	case 0xe1:	/* Loop */
	case 0xe2:	/* Loop */
	case 0xe3:	/* J*CXZ */
		p->ainsn.emulate_op = kprobe_emulate_loop;
		p->ainsn.loop.type = opcode & 0x3;
		p->ainsn.loop.asize = insn->addr_bytes * 8;
		p->ainsn.rel32 = *(s8 *)&insn->immediate.value;
		break;
	case 0xff:
		/*
		 * Since the 0xff is an extended group opcode, the instruction
		 * is determined by the MOD/RM byte.
		 */
		opcode = insn->modrm.bytes[0];
		switch (X86_MODRM_REG(opcode)) {
		case 0b010:	/* FF /2, call near, absolute indirect */
			p->ainsn.emulate_op = kprobe_emulate_call_indirect;
			break;
		case 0b100:	/* FF /4, jmp near, absolute indirect */
			p->ainsn.emulate_op = kprobe_emulate_jmp_indirect;
			break;
		case 0b011:	/* FF /3, call far, absolute indirect */
		case 0b101:	/* FF /5, jmp far, absolute indirect */
			return -EOPNOTSUPP;
		}

		if (!p->ainsn.emulate_op)
			break;

		if (insn->addr_bytes != sizeof(unsigned long))
			return -EOPNOTSUPP;	/* Don't support different size */
		if (X86_MODRM_MOD(opcode) != 3)
			return -EOPNOTSUPP;	/* TODO: support memory addressing */

		p->ainsn.indirect.reg = X86_MODRM_RM(opcode);
#ifdef CONFIG_X86_64
		if (X86_REX_B(insn->rex_prefix.value))
			p->ainsn.indirect.reg += 8;
#endif
		break;
	default:
		break;
	}
	p->ainsn.size = insn->length;

	return 0;
}

static int arch_copy_kprobe(struct kprobe *p)
{
	struct insn insn;
	kprobe_opcode_t buf[MAX_INSN_SIZE];
	int ret, len;

	/* Copy an instruction with recovering if other optprobe modifies it.*/
	len = __copy_instruction(buf, p->addr, p->ainsn.insn, &insn);
	if (!len)
		return -EINVAL;

	/* Analyze the opcode and setup emulate functions */
	ret = prepare_emulation(p, &insn);
	if (ret < 0)
		return ret;

	/* Add int3 for single-step or booster jmp */
	len = prepare_singlestep(buf, p, &insn);
	if (len < 0)
		return len;

	/* Also, displacement change doesn't affect the first byte */
	p->opcode = buf[0];

	p->ainsn.tp_len = len;
	perf_event_text_poke(p->ainsn.insn, NULL, 0, buf, len);

	/* OK, write back the instruction(s) into ROX insn buffer */
	text_poke(p->ainsn.insn, buf, len);

	return 0;
}

int arch_prepare_kprobe(struct kprobe *p)
{
	int ret;

	if (!can_probe((unsigned long)p->addr))
		return -EILSEQ;

	memset(&p->ainsn, 0, sizeof(p->ainsn));

	/* insn: must be on special executable page on x86. */
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn)
		return -ENOMEM;

	ret = arch_copy_kprobe(p);
	if (ret) {
		free_insn_slot(p->ainsn.insn, 0);
		p->ainsn.insn = NULL;
	}

	return ret;
}

void arch_arm_kprobe(struct kprobe *p)
{
	u8 int3 = INT3_INSN_OPCODE;

	text_poke(p->addr, &int3, 1);
	smp_text_poke_sync_each_cpu();
	perf_event_text_poke(p->addr, &p->opcode, 1, &int3, 1);
}

void arch_disarm_kprobe(struct kprobe *p)
{
	u8 int3 = INT3_INSN_OPCODE;

	perf_event_text_poke(p->addr, &int3, 1, &p->opcode, 1);
	text_poke(p->addr, &p->opcode, 1);
	smp_text_poke_sync_each_cpu();
}

void arch_remove_kprobe(struct kprobe *p)
{
	if (p->ainsn.insn) {
		/* Record the perf event before freeing the slot */
		perf_event_text_poke(p->ainsn.insn, p->ainsn.insn,
				     p->ainsn.tp_len, NULL, 0);
		free_insn_slot(p->ainsn.insn, p->ainsn.boostable);
		p->ainsn.insn = NULL;
	}
}

static nokprobe_inline void
save_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	kcb->prev_kprobe.kp = kprobe_running();
	kcb->prev_kprobe.status = kcb->kprobe_status;
	kcb->prev_kprobe.old_flags = kcb->kprobe_old_flags;
	kcb->prev_kprobe.saved_flags = kcb->kprobe_saved_flags;
}

static nokprobe_inline void
restore_previous_kprobe(struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
	kcb->kprobe_status = kcb->prev_kprobe.status;
	kcb->kprobe_old_flags = kcb->prev_kprobe.old_flags;
	kcb->kprobe_saved_flags = kcb->prev_kprobe.saved_flags;
}

static nokprobe_inline void
set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
		   struct kprobe_ctlblk *kcb)
{
	__this_cpu_write(current_kprobe, p);
	kcb->kprobe_saved_flags = kcb->kprobe_old_flags
		= (regs->flags & X86_EFLAGS_IF);
}

static void kprobe_post_process(struct kprobe *cur, struct pt_regs *regs,
			       struct kprobe_ctlblk *kcb)
{
	/* Restore back the original saved kprobes variables and continue. */
	if (kcb->kprobe_status == KPROBE_REENTER) {
		/* This will restore both kcb and current_kprobe */
		restore_previous_kprobe(kcb);
	} else {
		/*
		 * Always update the kcb status because
		 * reset_curent_kprobe() doesn't update kcb.
		 */
		kcb->kprobe_status = KPROBE_HIT_SSDONE;
		if (cur->post_handler)
			cur->post_handler(cur, regs, 0);
		reset_current_kprobe();
	}
}
NOKPROBE_SYMBOL(kprobe_post_process);

static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
			     struct kprobe_ctlblk *kcb, int reenter)
{
	if (setup_detour_execution(p, regs, reenter))
		return;

#if !defined(CONFIG_PREEMPTION)
	if (p->ainsn.boostable) {
		/* Boost up -- we can execute copied instructions directly */
		if (!reenter)
			reset_current_kprobe();
		/*
		 * Reentering boosted probe doesn't reset current_kprobe,
		 * nor set current_kprobe, because it doesn't use single
		 * stepping.
		 */
		regs->ip = (unsigned long)p->ainsn.insn;
		return;
	}
#endif
	if (reenter) {
		save_previous_kprobe(kcb);
		set_current_kprobe(p, regs, kcb);
		kcb->kprobe_status = KPROBE_REENTER;
	} else
		kcb->kprobe_status = KPROBE_HIT_SS;

	if (p->ainsn.emulate_op) {
		p->ainsn.emulate_op(p, regs);
		kprobe_post_process(p, regs, kcb);
		return;
	}

	/* Disable interrupt, and set ip register on trampoline */
	regs->flags &= ~X86_EFLAGS_IF;
	regs->ip = (unsigned long)p->ainsn.insn;
}
NOKPROBE_SYMBOL(setup_singlestep);

/*
 * Called after single-stepping.  p->addr is the address of the
 * instruction whose first byte has been replaced by the "int3"
 * instruction.  To avoid the SMP problems that can occur when we
 * temporarily put back the original opcode to single-step, we
 * single-stepped a copy of the instruction.  The address of this
 * copy is p->ainsn.insn. We also doesn't use trap, but "int3" again
 * right after the copied instruction.
 * Different from the trap single-step, "int3" single-step can not
 * handle the instruction which changes the ip register, e.g. jmp,
 * call, conditional jmp, and the instructions which changes the IF
 * flags because interrupt must be disabled around the single-stepping.
 * Such instructions are software emulated, but others are single-stepped
 * using "int3".
 *
 * When the 2nd "int3" handled, the regs->ip and regs->flags needs to
 * be adjusted, so that we can resume execution on correct code.
 */
static void resume_singlestep(struct kprobe *p, struct pt_regs *regs,
			      struct kprobe_ctlblk *kcb)
{
	unsigned long copy_ip = (unsigned long)p->ainsn.insn;
	unsigned long orig_ip = (unsigned long)p->addr;

	/* Restore saved interrupt flag and ip register */
	regs->flags |= kcb->kprobe_saved_flags;
	/* Note that regs->ip is executed int3 so must be a step back */
	regs->ip += (orig_ip - copy_ip) - INT3_INSN_SIZE;
}
NOKPROBE_SYMBOL(resume_singlestep);

/*
 * We have reentered the kprobe_handler(), since another probe was hit while
 * within the handler. We save the original kprobes variables and just single
 * step on the instruction of the new probe without calling any user handlers.
 */
static int reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
			  struct kprobe_ctlblk *kcb)
{
	switch (kcb->kprobe_status) {
	case KPROBE_HIT_SSDONE:
	case KPROBE_HIT_ACTIVE:
	case KPROBE_HIT_SS:
		kprobes_inc_nmissed_count(p);
		setup_singlestep(p, regs, kcb, 1);
		break;
	case KPROBE_REENTER:
		/* A probe has been hit in the codepath leading up to, or just
		 * after, single-stepping of a probed instruction. This entire
		 * codepath should strictly reside in .kprobes.text section.
		 * Raise a BUG or we'll continue in an endless reentering loop
		 * and eventually a stack overflow.
		 */
		pr_err("Unrecoverable kprobe detected.\n");
		dump_kprobe(p);
		BUG();
	default:
		/* impossible cases */
		WARN_ON(1);
		return 0;
	}

	return 1;
}
NOKPROBE_SYMBOL(reenter_kprobe);

static nokprobe_inline int kprobe_is_ss(struct kprobe_ctlblk *kcb)
{
	return (kcb->kprobe_status == KPROBE_HIT_SS ||
		kcb->kprobe_status == KPROBE_REENTER);
}

/*
 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
 * remain disabled throughout this function.
 */
int kprobe_int3_handler(struct pt_regs *regs)
{
	kprobe_opcode_t *addr;
	struct kprobe *p;
	struct kprobe_ctlblk *kcb;

	if (user_mode(regs))
		return 0;

	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
	/*
	 * We don't want to be preempted for the entire duration of kprobe
	 * processing. Since int3 and debug trap disables irqs and we clear
	 * IF while singlestepping, it must be no preemptible.
	 */

	kcb = get_kprobe_ctlblk();
	p = get_kprobe(addr);

	if (p) {
		if (kprobe_running()) {
			if (reenter_kprobe(p, regs, kcb))
				return 1;
		} else {
			set_current_kprobe(p, regs, kcb);
			kcb->kprobe_status = KPROBE_HIT_ACTIVE;

			/*
			 * If we have no pre-handler or it returned 0, we
			 * continue with normal processing.  If we have a
			 * pre-handler and it returned non-zero, that means
			 * user handler setup registers to exit to another
			 * instruction, we must skip the single stepping.
			 */
			if (!p->pre_handler || !p->pre_handler(p, regs))
				setup_singlestep(p, regs, kcb, 0);
			else
				reset_current_kprobe();
			return 1;
		}
	} else if (kprobe_is_ss(kcb)) {
		p = kprobe_running();
		if ((unsigned long)p->ainsn.insn < regs->ip &&
		    (unsigned long)p->ainsn.insn + MAX_INSN_SIZE > regs->ip) {
			/* Most provably this is the second int3 for singlestep */
			resume_singlestep(p, regs, kcb);
			kprobe_post_process(p, regs, kcb);
			return 1;
		}
	} /* else: not a kprobe fault; let the kernel handle it */

	return 0;
}
NOKPROBE_SYMBOL(kprobe_int3_handler);

int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
{
	struct kprobe *cur = kprobe_running();
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();

	if (unlikely(regs->ip == (unsigned long)cur->ainsn.insn)) {
		/* This must happen on single-stepping */
		WARN_ON(kcb->kprobe_status != KPROBE_HIT_SS &&
			kcb->kprobe_status != KPROBE_REENTER);
		/*
		 * We are here because the instruction being single
		 * stepped caused a page fault. We reset the current
		 * kprobe and the ip points back to the probe address
		 * and allow the page fault handler to continue as a
		 * normal page fault.
		 */
		regs->ip = (unsigned long)cur->addr;

		/*
		 * If the IF flag was set before the kprobe hit,
		 * don't touch it:
		 */
		regs->flags |= kcb->kprobe_old_flags;

		if (kcb->kprobe_status == KPROBE_REENTER)
			restore_previous_kprobe(kcb);
		else
			reset_current_kprobe();
	}

	return 0;
}
NOKPROBE_SYMBOL(kprobe_fault_handler);

int __init arch_populate_kprobe_blacklist(void)
{
	return kprobe_add_area_blacklist((unsigned long)__entry_text_start,
					 (unsigned long)__entry_text_end);
}

int __init arch_init_kprobes(void)
{
	return 0;
}

int arch_trampoline_kprobe(struct kprobe *p)
{
	return 0;
}