text: /*
   *  Kernel Probes (KProbes)
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   *
   * 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/extable.h>
  #include <linux/kdebug.h>
  #include <linux/kallsyms.h>
  #include <linux/ftrace.h>
  #include <linux/frame.h>
  #include <linux/kasan.h>
  #include <linux/moduleloader.h>
  
  #include <asm/text-patching.h>
  #include <asm/cacheflush.h>
  #include <asm/desc.h>
  #include <asm/pgtable.h>
  #include <linux/uaccess.h>
  #include <asm/alternative.h>
  #include <asm/insn.h>
  #include <asm/debugreg.h>
  #include <asm/set_memory.h>
  
  #include "common.h"
  
  DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
  DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
  
  #define stack_addr(regs) ((unsigned long *)kernel_stack_pointer(regs))
  
  #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, RELATIVEJUMP_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, RELATIVECALL_OPCODE);
  }
  NOKPROBE_SYMBOL(synthesize_relcall);
  
  /*
   * Skip the prefixes of the instruction.
   */
  static kprobe_opcode_t *skip_prefixes(kprobe_opcode_t *insn)
  {
  	insn_attr_t attr;
  
  	attr = inat_get_opcode_attribute((insn_byte_t)*insn);
  	while (inat_is_legacy_prefix(attr)) {
  		insn++;
  		attr = inat_get_opcode_attribute((insn_byte_t)*insn);
  	}
  #ifdef CONFIG_X86_64
  	if (inat_is_rex_prefix(attr))
  		insn++;
  #endif
  	return insn;
  }
  NOKPROBE_SYMBOL(skip_prefixes);
  
  /*
   * Returns non-zero if INSN is boostable.
   * RIP relative instructions are adjusted at copying time in 64 bits mode
   */
  int can_boost(struct insn *insn, void *addr)
  {
  	kprobe_opcode_t opcode;
  
  	if (search_exception_tables((unsigned long)addr))
  		return 0;	/* 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 0;
  
  	/* Can't boost Address-size override prefix */
  	if (unlikely(inat_is_address_size_prefix(insn->attr)))
  		return 0;
  
  	opcode = insn->opcode.bytes[0];
  
  	switch (opcode & 0xf0) {
  	case 0x60:
  		/* can't boost "bound" */
  		return (opcode != 0x62);
  	case 0x70:
  		return 0; /* can't boost conditional jump */
  	case 0x90:
  		return opcode != 0x9a;	/* can't boost call far */
  	case 0xc0:
  		/* can't boost software-interruptions */
  		return (0xc1 < opcode && opcode < 0xcc) || opcode == 0xcf;
  	case 0xd0:
  		/* can boost AA* and XLAT */
  		return (opcode == 0xd4 || opcode == 0xd5 || opcode == 0xd7);
  	case 0xe0:
  		/* can boost in/out and absolute jmps */
  		return ((opcode & 0x04) || opcode == 0xea);
  	case 0xf0:
  		/* clear and set flags are boostable */
  		return (opcode == 0xf5 || (0xf7 < opcode && opcode < 0xfe));
  	default:
  		/* CS override prefix and call are not boostable */
  		return (opcode != 0x2e && opcode != 0x9a);
  	}
  }
  
  static unsigned long
  __recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
  {
  	struct kprobe *kp;
  	unsigned long faddr;
  
  	kp = get_kprobe((void *)addr);
  	faddr = ftrace_location(addr);
  	/*
  	 * Addresses inside the ftrace location are refused by
  	 * arch_check_ftrace_location(). Something went terribly wrong
  	 * if such an address is checked here.
  	 */
  	if (WARN_ON(faddr && faddr != addr))
  		return 0UL;
  	/*
  	 * 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 (probe_kernel_read(buf, (void *)addr,
  		MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
  		return 0UL;
  
  	if (faddr)
  		memcpy(buf, ideal_nops[NOP_ATOMIC5], 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 paddr is at an instruction boundary */
  static int 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 0;
  
  	/* 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 0;
  		kernel_insn_init(&insn, (void *)__addr, MAX_INSN_SIZE);
  		insn_get_length(&insn);
  
  		/*
  		 * Another debugging subsystem might insert this breakpoint.
  		 * In that case, we can't recover it.
  		 */
  		if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
  			return 0;
  		addr += insn.length;
  	}
  
  	return (addr == paddr);
  }
  
  /*
   * Returns non-zero if opcode modifies the interrupt flag.
   */
  static int is_IF_modifier(kprobe_opcode_t *insn)
  {
  	/* Skip prefixes */
  	insn = skip_prefixes(insn);
  
  	switch (*insn) {
  	case 0xfa:		/* cli */
  	case 0xfb:		/* sti */
  	case 0xcf:		/* iret/iretd */
  	case 0x9d:		/* popf/popfd */
  		return 1;
  	}
  
  	return 0;
  }
  
  /*
   * 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);
  
  	if (!recovered_insn || !insn)
  		return 0;
  
  	/* This can access kernel text if given address is not recovered */
  	if (probe_kernel_read(dest, (void *)recovered_insn, MAX_INSN_SIZE))
  		return 0;
  
  	kernel_insn_init(insn, dest, MAX_INSN_SIZE);
  	insn_get_length(insn);
  
  	/* Another subsystem puts a breakpoint, failed to recover */
  	if (insn->opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
  		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 right after instruction to boost */
  static int prepare_boost(kprobe_opcode_t *buf, struct kprobe *p,
  			  struct insn *insn)
  {
  	int len = insn->length;
  
  	if (can_boost(insn, p->addr) &&
  	    MAX_INSN_SIZE - len >= RELATIVEJUMP_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 += RELATIVEJUMP_SIZE;
  		p->ainsn.boostable = true;
  	} else {
  		p->ainsn.boostable = false;
  	}
  
  	return len;
  }
  
  /* Make page to RO mode when allocate it */
  void *alloc_insn_page(void)
  {
  	void *page;
  
  	page = module_alloc(PAGE_SIZE);
  	if (!page)
  		return NULL;
  
  	/*
  	 * First make the page read-only, and only then make it executable to
  	 * prevent it from being W+X in between.
  	 */
  	set_memory_ro((unsigned long)page, 1);
  
  	/*
  	 * TODO: Once additional kernel code protection mechanisms are set, ensure
  	 * that the page was not maliciously altered and it is still zeroed.
  	 */
  	set_memory_x((unsigned long)page, 1);
  
  	return page;
  }
  
  /* Recover page to RW mode before releasing it */
  void free_insn_page(void *page)
  {
  	/*
  	 * First make the page non-executable, and only then make it writable to
  	 * prevent it from being W+X in between.
  	 */
  	set_memory_nx((unsigned long)page, 1);
  	set_memory_rw((unsigned long)page, 1);
  	module_memfree(page);
  }
  
  static int arch_copy_kprobe(struct kprobe *p)
  {
  	struct insn insn;
  	kprobe_opcode_t buf[MAX_INSN_SIZE];
  	int 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;
  
  	/*
  	 * __copy_instruction can modify the displacement of the instruction,
  	 * but it doesn't affect boostable check.
  	 */
  	len = prepare_boost(buf, p, &insn);
  
  	/* Check whether the instruction modifies Interrupt Flag or not */
  	p->ainsn.if_modifier = is_IF_modifier(buf);
  
  	/* Also, displacement change doesn't affect the first byte */
  	p->opcode = buf[0];
  
  	/* 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 (alternatives_text_reserved(p->addr, p->addr))
  		return -EINVAL;
  
  	if (!can_probe((unsigned long)p->addr))
  		return -EILSEQ;
  	/* 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)
  {
  	text_poke(p->addr, ((unsigned char []){BREAKPOINT_INSTRUCTION}), 1);
  }
  
  void arch_disarm_kprobe(struct kprobe *p)
  {
  	text_poke(p->addr, &p->opcode, 1);
  }
  
  void arch_remove_kprobe(struct kprobe *p)
  {
  	if (p->ainsn.insn) {
  		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_TF | X86_EFLAGS_IF));
  	if (p->ainsn.if_modifier)
  		kcb->kprobe_saved_flags &= ~X86_EFLAGS_IF;
  }
  
  static nokprobe_inline void clear_btf(void)
  {
  	if (test_thread_flag(TIF_BLOCKSTEP)) {
  		unsigned long debugctl = get_debugctlmsr();
  
  		debugctl &= ~DEBUGCTLMSR_BTF;
  		update_debugctlmsr(debugctl);
  	}
  }
  
  static nokprobe_inline void restore_btf(void)
  {
  	if (test_thread_flag(TIF_BLOCKSTEP)) {
  		unsigned long debugctl = get_debugctlmsr();
  
  		debugctl |= DEBUGCTLMSR_BTF;
  		update_debugctlmsr(debugctl);
  	}
  }
  
  void arch_prepare_kretprobe(struct kretprobe_instance *ri, struct pt_regs *regs)
  {
  	unsigned long *sara = stack_addr(regs);
  
  	ri->ret_addr = (kprobe_opcode_t *) *sara;
  	ri->fp = sara;
  
  	/* Replace the return addr with trampoline addr */
  	*sara = (unsigned long) &kretprobe_trampoline;
  }
  NOKPROBE_SYMBOL(arch_prepare_kretprobe);
  
  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_PREEMPT)
  	if (p->ainsn.boostable && !p->post_handler) {
  		/* 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;
  	/* Prepare real single stepping */
  	clear_btf();
  	regs->flags |= X86_EFLAGS_TF;
  	regs->flags &= ~X86_EFLAGS_IF;
  	/* single step inline if the instruction is an int3 */
  	if (p->opcode == BREAKPOINT_INSTRUCTION)
  		regs->ip = (unsigned long)p->addr;
  	else
  		regs->ip = (unsigned long)p->ainsn.insn;
  }
  NOKPROBE_SYMBOL(setup_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);
  
  /*
   * 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 (*addr != BREAKPOINT_INSTRUCTION) {
  		/*
  		 * The breakpoint instruction was removed right
  		 * after we hit it.  Another cpu has removed
  		 * either a probepoint or a debugger breakpoint
  		 * at this address.  In either case, no further
  		 * handling of this interrupt is appropriate.
  		 * Back up over the (now missing) int3 and run
  		 * the original instruction.
  		 */
  		regs->ip = (unsigned long)addr;
  		return 1;
  	} /* else: not a kprobe fault; let the kernel handle it */
  
  	return 0;
  }
  NOKPROBE_SYMBOL(kprobe_int3_handler);
  
  /*
   * When a retprobed function returns, this code saves registers and
   * calls trampoline_handler() runs, which calls the kretprobe's handler.
   */
  asm(
  	".global kretprobe_trampoline\n"
  	".type kretprobe_trampoline, @function\n"
  	"kretprobe_trampoline:\n"
  #ifdef CONFIG_X86_64
  	/* We don't bother saving the ss register */
  	"	pushq %rsp\n"
  	"	pushfq\n"
  	SAVE_REGS_STRING
  	"	movq %rsp, %rdi\n"
  	"	call trampoline_handler\n"
  	/* Replace saved sp with true return address. */
  	"	movq %rax, 152(%rsp)\n"
  	RESTORE_REGS_STRING
  	"	popfq\n"
  #else
  	"	pushf\n"
  	SAVE_REGS_STRING
  	"	movl %esp, %eax\n"
  	"	call trampoline_handler\n"
  	/* Move flags to cs */
  	"	movl 56(%esp), %edx\n"
  	"	movl %edx, 52(%esp)\n"
  	/* Replace saved flags with true return address. */
  	"	movl %eax, 56(%esp)\n"
  	RESTORE_REGS_STRING
  	"	popf\n"
  #endif
  	"	ret\n"
  	".size kretprobe_trampoline, .-kretprobe_trampoline\n"
  );
  NOKPROBE_SYMBOL(kretprobe_trampoline);
  STACK_FRAME_NON_STANDARD(kretprobe_trampoline);
  
  static struct kprobe kretprobe_kprobe = {
  	.addr = (void *)kretprobe_trampoline,
  };
  
  /*
   * Called from kretprobe_trampoline
   */
  static __used void *trampoline_handler(struct pt_regs *regs)
  {
  	struct kprobe_ctlblk *kcb;
  	struct kretprobe_instance *ri = NULL;
  	struct hlist_head *head, empty_rp;
  	struct hlist_node *tmp;
  	unsigned long flags, orig_ret_address = 0;
  	unsigned long trampoline_address = (unsigned long)&kretprobe_trampoline;
  	kprobe_opcode_t *correct_ret_addr = NULL;
  	void *frame_pointer;
  	bool skipped = false;
  
  	preempt_disable();
  
  	/*
  	 * Set a dummy kprobe for avoiding kretprobe recursion.
  	 * Since kretprobe never run in kprobe handler, kprobe must not
  	 * be running at this point.
  	 */
  	kcb = get_kprobe_ctlblk();
  	__this_cpu_write(current_kprobe, &kretprobe_kprobe);
  	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
  
  	INIT_HLIST_HEAD(&empty_rp);
  	kretprobe_hash_lock(current, &head, &flags);
  	/* fixup registers */
  #ifdef CONFIG_X86_64
  	regs->cs = __KERNEL_CS;
  	/* On x86-64, we use pt_regs->sp for return address holder. */
  	frame_pointer = &regs->sp;
  #else
  	regs->cs = __KERNEL_CS | get_kernel_rpl();
  	regs->gs = 0;
  	/* On x86-32, we use pt_regs->flags for return address holder. */
  	frame_pointer = &regs->flags;
  #endif
  	regs->ip = trampoline_address;
  	regs->orig_ax = ~0UL;
  
  	/*
  	 * It is possible to have multiple instances associated with a given
  	 * task either because multiple functions in the call path have
  	 * return probes installed on them, and/or more than one
  	 * return probe was registered for a target function.
  	 *
  	 * We can handle this because:
  	 *     - instances are always pushed into the head of the list
  	 *     - when multiple return probes are registered for the same
  	 *	 function, the (chronologically) first instance's ret_addr
  	 *	 will be the real return address, and all the rest will
  	 *	 point to kretprobe_trampoline.
  	 */
  	hlist_for_each_entry(ri, head, hlist) {
  		if (ri->task != current)
  			/* another task is sharing our hash bucket */
  			continue;
  		/*
  		 * Return probes must be pushed on this hash list correct
  		 * order (same as return order) so that it can be poped
  		 * correctly. However, if we find it is pushed it incorrect
  		 * order, this means we find a function which should not be
  		 * probed, because the wrong order entry is pushed on the
  		 * path of processing other kretprobe itself.
  		 */
  		if (ri->fp != frame_pointer) {
  			if (!skipped)
  				pr_warn("kretprobe is stacked incorrectly. Trying to fixup.\n");
  			skipped = true;
  			continue;
  		}
  
  		orig_ret_address = (unsigned long)ri->ret_addr;
  		if (skipped)
  			pr_warn("%ps must be blacklisted because of incorrect kretprobe order\n",
  				ri->rp->kp.addr);
  
  		if (orig_ret_address != trampoline_address)
  			/*
  			 * This is the real return address. Any other
  			 * instances associated with this task are for
  			 * other calls deeper on the call stack
  			 */
  			break;
  	}
  
  	kretprobe_assert(ri, orig_ret_address, trampoline_address);
  
  	correct_ret_addr = ri->ret_addr;
  	hlist_for_each_entry_safe(ri, tmp, head, hlist) {
  		if (ri->task != current)
  			/* another task is sharing our hash bucket */
  			continue;
  		if (ri->fp != frame_pointer)
  			continue;
  
  		orig_ret_address = (unsigned long)ri->ret_addr;
  		if (ri->rp && ri->rp->handler) {
  			__this_cpu_write(current_kprobe, &ri->rp->kp);
  			ri->ret_addr = correct_ret_addr;
  			ri->rp->handler(ri, regs);
  			__this_cpu_write(current_kprobe, &kretprobe_kprobe);
  		}
  
  		recycle_rp_inst(ri, &empty_rp);
  
  		if (orig_ret_address != trampoline_address)
  			/*
  			 * This is the real return address. Any other
  			 * instances associated with this task are for
  			 * other calls deeper on the call stack
  			 */
  			break;
  	}
  
  	kretprobe_hash_unlock(current, &flags);
  
  	__this_cpu_write(current_kprobe, NULL);
  	preempt_enable();
  
  	hlist_for_each_entry_safe(ri, tmp, &empty_rp, hlist) {
  		hlist_del(&ri->hlist);
  		kfree(ri);
  	}
  	return (void *)orig_ret_address;
  }
  NOKPROBE_SYMBOL(trampoline_handler);
  
  /*
   * Called after single-stepping.  p->addr is the address of the
   * instruction whose first byte has been replaced by the "int 3"
   * 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.
   *
   * This function prepares to return from the post-single-step
   * interrupt.  We have to fix up the stack as follows:
   *
   * 0) Except in the case of absolute or indirect jump or call instructions,
   * the new ip is relative to the copied instruction.  We need to make
   * it relative to the original instruction.
   *
   * 1) If the single-stepped instruction was pushfl, then the TF and IF
   * flags are set in the just-pushed flags, and may need to be cleared.
   *
   * 2) If the single-stepped instruction was a call, the return address
   * that is atop the stack is the address following the copied instruction.
   * We need to make it the address following the original instruction.
   *
   * If this is the first time we've single-stepped the instruction at
   * this probepoint, and the instruction is boostable, boost it: add a
   * jump instruction after the copied instruction, that jumps to the next
   * instruction after the probepoint.
   */
  static void resume_execution(struct kprobe *p, struct pt_regs *regs,
  			     struct kprobe_ctlblk *kcb)
  {
  	unsigned long *tos = stack_addr(regs);
  	unsigned long copy_ip = (unsigned long)p->ainsn.insn;
  	unsigned long orig_ip = (unsigned long)p->addr;
  	kprobe_opcode_t *insn = p->ainsn.insn;
  
  	/* Skip prefixes */
  	insn = skip_prefixes(insn);
  
  	regs->flags &= ~X86_EFLAGS_TF;
  	switch (*insn) {
  	case 0x9c:	/* pushfl */
  		*tos &= ~(X86_EFLAGS_TF | X86_EFLAGS_IF);
  		*tos |= kcb->kprobe_old_flags;
  		break;
  	case 0xc2:	/* iret/ret/lret */
  	case 0xc3:
  	case 0xca:
  	case 0xcb:
  	case 0xcf:
  	case 0xea:	/* jmp absolute -- ip is correct */
  		/* ip is already adjusted, no more changes required */
  		p->ainsn.boostable = true;
  		goto no_change;
  	case 0xe8:	/* call relative - Fix return addr */
  		*tos = orig_ip + (*tos - copy_ip);
  		break;
  #ifdef CONFIG_X86_32
  	case 0x9a:	/* call absolute -- same as call absolute, indirect */
  		*tos = orig_ip + (*tos - copy_ip);
  		goto no_change;
  #endif
  	case 0xff:
  		if ((insn[1] & 0x30) == 0x10) {
  			/*
  			 * call absolute, indirect
  			 * Fix return addr; ip is correct.
  			 * But this is not boostable
  			 */
  			*tos = orig_ip + (*tos - copy_ip);
  			goto no_change;
  		} else if (((insn[1] & 0x31) == 0x20) ||
  			   ((insn[1] & 0x31) == 0x21)) {
  			/*
  			 * jmp near and far, absolute indirect
  			 * ip is correct. And this is boostable
  			 */
  			p->ainsn.boostable = true;
  			goto no_change;
  		}
  	default:
  		break;
  	}
  
  	regs->ip += orig_ip - copy_ip;
  
  no_change:
  	restore_btf();
  }
  NOKPROBE_SYMBOL(resume_execution);
  
  /*
   * Interrupts are disabled on entry as trap1 is an interrupt gate and they
   * remain disabled throughout this function.
   */
  int kprobe_debug_handler(struct pt_regs *regs)
  {
  	struct kprobe *cur = kprobe_running();
  	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
  
  	if (!cur)
  		return 0;
  
  	resume_execution(cur, regs, kcb);
  	regs->flags |= kcb->kprobe_saved_flags;
  
  	if ((kcb->kprobe_status != KPROBE_REENTER) && cur->post_handler) {
  		kcb->kprobe_status = KPROBE_HIT_SSDONE;
  		cur->post_handler(cur, regs, 0);
  	}
  
  	/* Restore back the original saved kprobes variables and continue. */
  	if (kcb->kprobe_status == KPROBE_REENTER) {
  		restore_previous_kprobe(kcb);
  		goto out;
  	}
  	reset_current_kprobe();
  out:
  	/*
  	 * if somebody else is singlestepping across a probe point, flags
  	 * will have TF set, in which case, continue the remaining processing
  	 * of do_debug, as if this is not a probe hit.
  	 */
  	if (regs->flags & X86_EFLAGS_TF)
  		return 0;
  
  	return 1;
  }
  NOKPROBE_SYMBOL(kprobe_debug_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;
  		/*
  		 * Trap flag (TF) has been set here because this fault
  		 * happened where the single stepping will be done.
  		 * So clear it by resetting the current kprobe:
  		 */
  		regs->flags &= ~X86_EFLAGS_TF;
  
  		/*
  		 * If the TF 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();
  	} else if (kcb->kprobe_status == KPROBE_HIT_ACTIVE ||
  		   kcb->kprobe_status == KPROBE_HIT_SSDONE) {
  		/*
  		 * We increment the nmissed count for accounting,
  		 * we can also use npre/npostfault count for accounting
  		 * these specific fault cases.
  		 */
  		kprobes_inc_nmissed_count(cur);
  
  		/*
  		 * We come here because instructions in the pre/post
  		 * handler caused the page_fault, this could happen
  		 * if handler tries to access user space by
  		 * copy_from_user(), get_user() etc. Let the
  		 * user-specified handler try to fix it first.
  		 */
  		if (cur->fault_handler && cur->fault_handler(cur, regs, trapnr))
  			return 1;
  	}
  
  	return 0;
  }
  NOKPROBE_SYMBOL(kprobe_fault_handler);
  
  int __init arch_populate_kprobe_blacklist(void)
  {
  	int ret;
  
  	ret = kprobe_add_area_blacklist((unsigned long)__irqentry_text_start,
  					 (unsigned long)__irqentry_text_end);
  	if (ret)
  		return ret;
  
  	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;
  }
  