arch/s390/kernel/kprobes.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  *  Kernel Probes (KProbes)
  *
  * Copyright IBM Corp. 2002, 2006
  *
  * s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
  */

 #define pr_fmt(fmt) "kprobes: " fmt

 #include <linux/kprobes.h>
 #include <linux/ptrace.h>
 #include <linux/preempt.h>
 #include <linux/stop_machine.h>
 #include <linux/kdebug.h>
 #include <linux/uaccess.h>
 #include <linux/extable.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/hardirq.h>
 #include <linux/ftrace.h>
 #include <linux/execmem.h>
 #include <asm/text-patching.h>
 #include <asm/set_memory.h>
 #include <asm/sections.h>
 #include <asm/dis.h>
 #include "entry.h"

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

 struct kretprobe_blackpoint kretprobe_blacklist[] = { };

 void *alloc_insn_page(void)
 {
 	void *page;

 	page = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
 	if (!page)
 		return NULL;
 	set_memory_rox((unsigned long)page, 1);
 	return page;
 }

 static void copy_instruction(struct kprobe *p)
 {
 	kprobe_opcode_t insn[MAX_INSN_SIZE];
 	s64 disp, new_disp;
 	u64 addr, new_addr;
 	unsigned int len;

 	len = insn_length(*p->addr >> 8);
 	memcpy(&insn, p->addr, len);
 	p->opcode = insn[0];
 	if (probe_is_insn_relative_long(&insn[0])) {
 		/*
 		 * For pc-relative instructions in RIL-b or RIL-c format patch
 		 * the RI2 displacement field. The insn slot for the to be
 		 * patched instruction is within the same 4GB area like the
 		 * original instruction. Therefore the new displacement will
 		 * always fit.
 		 */
 		disp = *(s32 *)&insn[1];
 		addr = (u64)(unsigned long)p->addr;
 		new_addr = (u64)(unsigned long)p->ainsn.insn;
 		new_disp = ((addr + (disp * 2)) - new_addr) / 2;
 		*(s32 *)&insn[1] = new_disp;
 	}
 	s390_kernel_write(p->ainsn.insn, &insn, len);
 }
 NOKPROBE_SYMBOL(copy_instruction);

 /* Check if paddr is at an instruction boundary */
 static bool can_probe(unsigned long paddr)
 {
 	unsigned long addr, offset = 0;
 	kprobe_opcode_t insn;
 	struct kprobe *kp;

 	if (paddr & 0x01)
 		return false;

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

 	/* Decode instructions */
 	addr = paddr - offset;
 	while (addr < paddr) {
 		if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(insn)))
 			return false;

 		if (insn >> 8 == 0) {
 			if (insn != BREAKPOINT_INSTRUCTION) {
 				/*
 				 * Note that QEMU inserts opcode 0x0000 to implement
 				 * software breakpoints for guests. Since the size of
 				 * the original instruction is unknown, stop following
 				 * instructions and prevent setting a kprobe.
 				 */
 				return false;
 			}
 			/*
 			 * Check if the instruction has been modified by another
 			 * kprobe, in which case the original instruction is
 			 * decoded.
 			 */
 			kp = get_kprobe((void *)addr);
 			if (!kp) {
 				/* not a kprobe */
 				return false;
 			}
 			insn = kp->opcode;
 		}
 		addr += insn_length(insn >> 8);
 	}
 	return addr == paddr;
 }

 int arch_prepare_kprobe(struct kprobe *p)
 {
 	if (!can_probe((unsigned long)p->addr))
 		return -EINVAL;
 	/* Make sure the probe isn't going on a difficult instruction */
 	if (probe_is_prohibited_opcode(p->addr))
 		return -EINVAL;
 	p->ainsn.insn = get_insn_slot();
 	if (!p->ainsn.insn)
 		return -ENOMEM;
 	copy_instruction(p);
 	return 0;
 }
 NOKPROBE_SYMBOL(arch_prepare_kprobe);

 struct swap_insn_args {
 	struct kprobe *p;
 	unsigned int arm_kprobe : 1;
 };

 static int swap_instruction(void *data)
 {
 	struct swap_insn_args *args = data;
 	struct kprobe *p = args->p;
 	u16 opc;

 	opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
 	s390_kernel_write(p->addr, &opc, sizeof(opc));
 	return 0;
 }
 NOKPROBE_SYMBOL(swap_instruction);

 void arch_arm_kprobe(struct kprobe *p)
 {
 	struct swap_insn_args args = {.p = p, .arm_kprobe = 1};

 	if (MACHINE_HAS_SEQ_INSN) {
 		swap_instruction(&args);
 		text_poke_sync();
 	} else {
 		stop_machine_cpuslocked(swap_instruction, &args, NULL);
 	}
 }
 NOKPROBE_SYMBOL(arch_arm_kprobe);

 void arch_disarm_kprobe(struct kprobe *p)
 {
 	struct swap_insn_args args = {.p = p, .arm_kprobe = 0};

 	if (MACHINE_HAS_SEQ_INSN) {
 		swap_instruction(&args);
 		text_poke_sync();
 	} else {
 		stop_machine_cpuslocked(swap_instruction, &args, NULL);
 	}
 }
 NOKPROBE_SYMBOL(arch_disarm_kprobe);

 void arch_remove_kprobe(struct kprobe *p)
 {
 	if (!p->ainsn.insn)
 		return;
 	free_insn_slot(p->ainsn.insn, 0);
 	p->ainsn.insn = NULL;
 }
 NOKPROBE_SYMBOL(arch_remove_kprobe);

 static void enable_singlestep(struct kprobe_ctlblk *kcb,
 			      struct pt_regs *regs,
 			      unsigned long ip)
 {
 	union {
 		struct ctlreg regs[3];
 		struct {
 			struct ctlreg control;
 			struct ctlreg start;
 			struct ctlreg end;
 		};
 	} per_kprobe;

 	/* Set up the PER control registers %cr9-%cr11 */
 	per_kprobe.control.val = PER_EVENT_IFETCH;
 	per_kprobe.start.val = ip;
 	per_kprobe.end.val = ip;

 	/* Save control regs and psw mask */
 	__local_ctl_store(9, 11, kcb->kprobe_saved_ctl);
 	kcb->kprobe_saved_imask = regs->psw.mask &
 		(PSW_MASK_PER | PSW_MASK_IO | PSW_MASK_EXT);

 	/* Set PER control regs, turns on single step for the given address */
 	__local_ctl_load(9, 11, per_kprobe.regs);
 	regs->psw.mask |= PSW_MASK_PER;
 	regs->psw.mask &= ~(PSW_MASK_IO | PSW_MASK_EXT);
 	regs->psw.addr = ip;
 }
 NOKPROBE_SYMBOL(enable_singlestep);

 static void disable_singlestep(struct kprobe_ctlblk *kcb,
 			       struct pt_regs *regs,
 			       unsigned long ip)
 {
 	/* Restore control regs and psw mask, set new psw address */
 	__local_ctl_load(9, 11, kcb->kprobe_saved_ctl);
 	regs->psw.mask &= ~PSW_MASK_PER;
 	regs->psw.mask |= kcb->kprobe_saved_imask;
 	regs->psw.addr = ip;
 }
 NOKPROBE_SYMBOL(disable_singlestep);

 /*
  * Activate a kprobe by storing its pointer to current_kprobe. The
  * previous kprobe is stored in kcb->prev_kprobe. A stack of up to
  * two kprobes can be active, see KPROBE_REENTER.
  */
 static void push_kprobe(struct kprobe_ctlblk *kcb, struct kprobe *p)
 {
 	kcb->prev_kprobe.kp = __this_cpu_read(current_kprobe);
 	kcb->prev_kprobe.status = kcb->kprobe_status;
 	__this_cpu_write(current_kprobe, p);
 }
 NOKPROBE_SYMBOL(push_kprobe);

 /*
  * Deactivate a kprobe by backing up to the previous state. If the
  * current state is KPROBE_REENTER prev_kprobe.kp will be non-NULL,
  * for any other state prev_kprobe.kp will be NULL.
  */
 static void pop_kprobe(struct kprobe_ctlblk *kcb)
 {
 	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
 	kcb->kprobe_status = kcb->prev_kprobe.status;
 	kcb->prev_kprobe.kp = NULL;
 }
 NOKPROBE_SYMBOL(pop_kprobe);

 static void kprobe_reenter_check(struct kprobe_ctlblk *kcb, struct kprobe *p)
 {
 	switch (kcb->kprobe_status) {
 	case KPROBE_HIT_SSDONE:
 	case KPROBE_HIT_ACTIVE:
 		kprobes_inc_nmissed_count(p);
 		break;
 	case KPROBE_HIT_SS:
 	case KPROBE_REENTER:
 	default:
 		/*
 		 * A kprobe on the code path to single step an instruction
 		 * is a BUG. The code path resides in the .kprobes.text
 		 * section and is executed with interrupts disabled.
 		 */
 		pr_err("Failed to recover from reentered kprobes.\n");
 		dump_kprobe(p);
 		BUG();
 	}
 }
 NOKPROBE_SYMBOL(kprobe_reenter_check);

 static int kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb;
 	struct kprobe *p;

 	/*
 	 * We want to disable preemption for the entire duration of kprobe
 	 * processing. That includes the calls to the pre/post handlers
 	 * and single stepping the kprobe instruction.
 	 */
 	preempt_disable();
 	kcb = get_kprobe_ctlblk();
 	p = get_kprobe((void *)(regs->psw.addr - 2));

 	if (p) {
 		if (kprobe_running()) {
 			/*
 			 * We have hit a kprobe while another is still
 			 * active. This can happen in the pre and post
 			 * handler. Single step the instruction of the
 			 * new probe but do not call any handler function
 			 * of this secondary kprobe.
 			 * push_kprobe and pop_kprobe saves and restores
 			 * the currently active kprobe.
 			 */
 			kprobe_reenter_check(kcb, p);
 			push_kprobe(kcb, p);
 			kcb->kprobe_status = KPROBE_REENTER;
 		} else {
 			/*
 			 * If we have no pre-handler or it returned 0, we
 			 * continue with single stepping. If we have a
 			 * pre-handler and it returned non-zero, it prepped
 			 * for changing execution path, so get out doing
 			 * nothing more here.
 			 */
 			push_kprobe(kcb, p);
 			kcb->kprobe_status = KPROBE_HIT_ACTIVE;
 			if (p->pre_handler && p->pre_handler(p, regs)) {
 				pop_kprobe(kcb);
 				preempt_enable_no_resched();
 				return 1;
 			}
 			kcb->kprobe_status = KPROBE_HIT_SS;
 		}
 		enable_singlestep(kcb, regs, (unsigned long) p->ainsn.insn);
 		return 1;
 	} /* else:
 	   * No kprobe at this address and no active kprobe. The trap has
 	   * not been caused by a kprobe breakpoint. The race of breakpoint
 	   * vs. kprobe remove does not exist because on s390 as we use
 	   * stop_machine to arm/disarm the breakpoints.
 	   */
 	preempt_enable_no_resched();
 	return 0;
 }
 NOKPROBE_SYMBOL(kprobe_handler);

 /*
  * Called after single-stepping.  p->addr is the address of the
  * instruction whose first byte has been replaced by the "breakpoint"
  * 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.
  */
 static void resume_execution(struct kprobe *p, struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	unsigned long ip = regs->psw.addr;
 	int fixup = probe_get_fixup_type(p->ainsn.insn);

 	if (fixup & FIXUP_PSW_NORMAL)
 		ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;

 	if (fixup & FIXUP_BRANCH_NOT_TAKEN) {
 		int ilen = insn_length(p->ainsn.insn[0] >> 8);
 		if (ip - (unsigned long) p->ainsn.insn == ilen)
 			ip = (unsigned long) p->addr + ilen;
 	}

 	if (fixup & FIXUP_RETURN_REGISTER) {
 		int reg = (p->ainsn.insn[0] & 0xf0) >> 4;
 		regs->gprs[reg] += (unsigned long) p->addr -
 				   (unsigned long) p->ainsn.insn;
 	}

 	disable_singlestep(kcb, regs, ip);
 }
 NOKPROBE_SYMBOL(resume_execution);

 static int post_kprobe_handler(struct pt_regs *regs)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	struct kprobe *p = kprobe_running();

 	if (!p)
 		return 0;

 	resume_execution(p, regs);
 	if (kcb->kprobe_status != KPROBE_REENTER && p->post_handler) {
 		kcb->kprobe_status = KPROBE_HIT_SSDONE;
 		p->post_handler(p, regs, 0);
 	}
 	pop_kprobe(kcb);
 	preempt_enable_no_resched();

 	/*
 	 * if somebody else is singlestepping across a probe point, psw mask
 	 * will have PER set, in which case, continue the remaining processing
 	 * of do_single_step, as if this is not a probe hit.
 	 */
 	if (regs->psw.mask & PSW_MASK_PER)
 		return 0;

 	return 1;
 }
 NOKPROBE_SYMBOL(post_kprobe_handler);

 static int kprobe_trap_handler(struct pt_regs *regs, int trapnr)
 {
 	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
 	struct kprobe *p = kprobe_running();

 	switch(kcb->kprobe_status) {
 	case KPROBE_HIT_SS:
 	case KPROBE_REENTER:
 		/*
 		 * We are here because the instruction being single
 		 * stepped caused a page fault. We reset the current
 		 * kprobe and the nip points back to the probe address
 		 * and allow the page fault handler to continue as a
 		 * normal page fault.
 		 */
 		disable_singlestep(kcb, regs, (unsigned long) p->addr);
 		pop_kprobe(kcb);
 		preempt_enable_no_resched();
 		break;
 	case KPROBE_HIT_ACTIVE:
 	case KPROBE_HIT_SSDONE:
 		/*
 		 * In case the user-specified fault handler returned
 		 * zero, try to fix up.
 		 */
 		if (fixup_exception(regs))
 			return 1;
 		/*
 		 * fixup_exception() could not handle it,
 		 * Let do_page_fault() fix it.
 		 */
 		break;
 	default:
 		break;
 	}
 	return 0;
 }
 NOKPROBE_SYMBOL(kprobe_trap_handler);

 int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
 {
 	int ret;

 	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
 		local_irq_disable();
 	ret = kprobe_trap_handler(regs, trapnr);
 	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
 		local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);
 	return ret;
 }
 NOKPROBE_SYMBOL(kprobe_fault_handler);

 /*
  * Wrapper routine to for handling exceptions.
  */
 int kprobe_exceptions_notify(struct notifier_block *self,
 			     unsigned long val, void *data)
 {
 	struct die_args *args = (struct die_args *) data;
 	struct pt_regs *regs = args->regs;
 	int ret = NOTIFY_DONE;

 	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
 		local_irq_disable();

 	switch (val) {
 	case DIE_BPT:
 		if (kprobe_handler(regs))
 			ret = NOTIFY_STOP;
 		break;
 	case DIE_SSTEP:
 		if (post_kprobe_handler(regs))
 			ret = NOTIFY_STOP;
 		break;
 	case DIE_TRAP:
 		if (!preemptible() && kprobe_running() &&
 		    kprobe_trap_handler(regs, args->trapnr))
 			ret = NOTIFY_STOP;
 		break;
 	default:
 		break;
 	}

 	if (regs->psw.mask & (PSW_MASK_IO | PSW_MASK_EXT))
 		local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);

 	return ret;
 }
 NOKPROBE_SYMBOL(kprobe_exceptions_notify);

 int __init arch_init_kprobes(void)
 {
 	return 0;
 }

 int arch_trampoline_kprobe(struct kprobe *p)
 {
 	return 0;
 }
 NOKPROBE_SYMBOL(arch_trampoline_kprobe);
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* Kernel Probes (KProbes)
	*
	* Copyright IBM Corp. 2002, 2006
	*
	* s390 port, used ppc64 as template. Mike Grundy <grundym@us.ibm.com>
	*/

	#define pr_fmt(fmt) "kprobes: " fmt

	#include <linux/kprobes.h>
	#include <linux/ptrace.h>
	#include <linux/preempt.h>
	#include <linux/stop_machine.h>
	#include <linux/kdebug.h>
	#include <linux/uaccess.h>
	#include <linux/extable.h>
	#include <linux/module.h>
	#include <linux/slab.h>
	#include <linux/hardirq.h>
	#include <linux/ftrace.h>
	#include <linux/execmem.h>
	#include <asm/text-patching.h>
	#include <asm/set_memory.h>
	#include <asm/sections.h>
	#include <asm/dis.h>
	#include "entry.h"

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

	struct kretprobe_blackpoint kretprobe_blacklist[] = { };

	void *alloc_insn_page(void)
	{
	void *page;

	page = execmem_alloc(EXECMEM_KPROBES, PAGE_SIZE);
	if (!page)
	return NULL;
	set_memory_rox((unsigned long)page, 1);
	return page;
	}

	static void copy_instruction(struct kprobe *p)
	{
	kprobe_opcode_t insn[MAX_INSN_SIZE];
	s64 disp, new_disp;
	u64 addr, new_addr;
	unsigned int len;

	len = insn_length(*p->addr >> 8);
	memcpy(&insn, p->addr, len);
	p->opcode = insn[0];
	if (probe_is_insn_relative_long(&insn[0])) {
	/*
	* For pc-relative instructions in RIL-b or RIL-c format patch
	* the RI2 displacement field. The insn slot for the to be
	* patched instruction is within the same 4GB area like the
	* original instruction. Therefore the new displacement will
	* always fit.
	*/
	disp = (s32 )&insn[1];
	addr = (u64)(unsigned long)p->addr;
	new_addr = (u64)(unsigned long)p->ainsn.insn;
	new_disp = ((addr + (disp * 2)) - new_addr) / 2;
	(s32 )&insn[1] = new_disp;
	}
	s390_kernel_write(p->ainsn.insn, &insn, len);
	}
	NOKPROBE_SYMBOL(copy_instruction);

	/* Check if paddr is at an instruction boundary */
	static bool can_probe(unsigned long paddr)
	{
	unsigned long addr, offset = 0;
	kprobe_opcode_t insn;
	struct kprobe *kp;

	if (paddr & 0x01)
	return false;

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

	/* Decode instructions */
	addr = paddr - offset;
	while (addr < paddr) {
	if (copy_from_kernel_nofault(&insn, (void *)addr, sizeof(insn)))
	return false;

	if (insn >> 8 == 0) {
	if (insn != BREAKPOINT_INSTRUCTION) {
	/*
	* Note that QEMU inserts opcode 0x0000 to implement
	* software breakpoints for guests. Since the size of
	* the original instruction is unknown, stop following
	* instructions and prevent setting a kprobe.
	*/
	return false;
	}
	/*
	* Check if the instruction has been modified by another
	* kprobe, in which case the original instruction is
	* decoded.
	*/
	kp = get_kprobe((void *)addr);
	if (!kp) {
	/* not a kprobe */
	return false;
	}
	insn = kp->opcode;
	}
	addr += insn_length(insn >> 8);
	}
	return addr == paddr;
	}

	int arch_prepare_kprobe(struct kprobe *p)
	{
	if (!can_probe((unsigned long)p->addr))
	return -EINVAL;
	/* Make sure the probe isn't going on a difficult instruction */
	if (probe_is_prohibited_opcode(p->addr))
	return -EINVAL;
	p->ainsn.insn = get_insn_slot();
	if (!p->ainsn.insn)
	return -ENOMEM;
	copy_instruction(p);
	return 0;
	}
	NOKPROBE_SYMBOL(arch_prepare_kprobe);

	struct swap_insn_args {
	struct kprobe *p;
	unsigned int arm_kprobe : 1;
	};

	static int swap_instruction(void *data)
	{
	struct swap_insn_args *args = data;
	struct kprobe *p = args->p;
	u16 opc;

	opc = args->arm_kprobe ? BREAKPOINT_INSTRUCTION : p->opcode;
	s390_kernel_write(p->addr, &opc, sizeof(opc));
	return 0;
	}
	NOKPROBE_SYMBOL(swap_instruction);

	void arch_arm_kprobe(struct kprobe *p)
	{
	struct swap_insn_args args = {.p = p, .arm_kprobe = 1};

	if (MACHINE_HAS_SEQ_INSN) {
	swap_instruction(&args);
	text_poke_sync();
	} else {
	stop_machine_cpuslocked(swap_instruction, &args, NULL);
	}
	}
	NOKPROBE_SYMBOL(arch_arm_kprobe);

	void arch_disarm_kprobe(struct kprobe *p)
	{
	struct swap_insn_args args = {.p = p, .arm_kprobe = 0};

	if (MACHINE_HAS_SEQ_INSN) {
	swap_instruction(&args);
	text_poke_sync();
	} else {
	stop_machine_cpuslocked(swap_instruction, &args, NULL);
	}
	}
	NOKPROBE_SYMBOL(arch_disarm_kprobe);

	void arch_remove_kprobe(struct kprobe *p)
	{
	if (!p->ainsn.insn)
	return;
	free_insn_slot(p->ainsn.insn, 0);
	p->ainsn.insn = NULL;
	}
	NOKPROBE_SYMBOL(arch_remove_kprobe);

	static void enable_singlestep(struct kprobe_ctlblk *kcb,
	struct pt_regs *regs,
	unsigned long ip)
	{
	union {
	struct ctlreg regs[3];
	struct {
	struct ctlreg control;
	struct ctlreg start;
	struct ctlreg end;
	};
	} per_kprobe;

	/* Set up the PER control registers %cr9-%cr11 */
	per_kprobe.control.val = PER_EVENT_IFETCH;
	per_kprobe.start.val = ip;
	per_kprobe.end.val = ip;

	/* Save control regs and psw mask */
	__local_ctl_store(9, 11, kcb->kprobe_saved_ctl);
	kcb->kprobe_saved_imask = regs->psw.mask &
	(PSW_MASK_PER \| PSW_MASK_IO \| PSW_MASK_EXT);

	/* Set PER control regs, turns on single step for the given address */
	__local_ctl_load(9, 11, per_kprobe.regs);
	regs->psw.mask \|= PSW_MASK_PER;
	regs->psw.mask &= ~(PSW_MASK_IO \| PSW_MASK_EXT);
	regs->psw.addr = ip;
	}
	NOKPROBE_SYMBOL(enable_singlestep);

	static void disable_singlestep(struct kprobe_ctlblk *kcb,
	struct pt_regs *regs,
	unsigned long ip)
	{
	/* Restore control regs and psw mask, set new psw address */
	__local_ctl_load(9, 11, kcb->kprobe_saved_ctl);
	regs->psw.mask &= ~PSW_MASK_PER;
	regs->psw.mask \|= kcb->kprobe_saved_imask;
	regs->psw.addr = ip;
	}
	NOKPROBE_SYMBOL(disable_singlestep);

	/*
	* Activate a kprobe by storing its pointer to current_kprobe. The
	* previous kprobe is stored in kcb->prev_kprobe. A stack of up to
	* two kprobes can be active, see KPROBE_REENTER.
	*/
	static void push_kprobe(struct kprobe_ctlblk kcb, struct kprobe p)
	{
	kcb->prev_kprobe.kp = __this_cpu_read(current_kprobe);
	kcb->prev_kprobe.status = kcb->kprobe_status;
	__this_cpu_write(current_kprobe, p);
	}
	NOKPROBE_SYMBOL(push_kprobe);

	/*
	* Deactivate a kprobe by backing up to the previous state. If the
	* current state is KPROBE_REENTER prev_kprobe.kp will be non-NULL,
	* for any other state prev_kprobe.kp will be NULL.
	*/
	static void pop_kprobe(struct kprobe_ctlblk *kcb)
	{
	__this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
	kcb->kprobe_status = kcb->prev_kprobe.status;
	kcb->prev_kprobe.kp = NULL;
	}
	NOKPROBE_SYMBOL(pop_kprobe);

	static void kprobe_reenter_check(struct kprobe_ctlblk kcb, struct kprobe p)
	{
	switch (kcb->kprobe_status) {
	case KPROBE_HIT_SSDONE:
	case KPROBE_HIT_ACTIVE:
	kprobes_inc_nmissed_count(p);
	break;
	case KPROBE_HIT_SS:
	case KPROBE_REENTER:
	default:
	/*
	* A kprobe on the code path to single step an instruction
	* is a BUG. The code path resides in the .kprobes.text
	* section and is executed with interrupts disabled.
	*/
	pr_err("Failed to recover from reentered kprobes.\n");
	dump_kprobe(p);
	BUG();
	}
	}
	NOKPROBE_SYMBOL(kprobe_reenter_check);

	static int kprobe_handler(struct pt_regs *regs)
	{
	struct kprobe_ctlblk *kcb;
	struct kprobe *p;

	/*
	* We want to disable preemption for the entire duration of kprobe
	* processing. That includes the calls to the pre/post handlers
	* and single stepping the kprobe instruction.
	*/
	preempt_disable();
	kcb = get_kprobe_ctlblk();
	p = get_kprobe((void *)(regs->psw.addr - 2));

	if (p) {
	if (kprobe_running()) {
	/*
	* We have hit a kprobe while another is still
	* active. This can happen in the pre and post
	* handler. Single step the instruction of the
	* new probe but do not call any handler function
	* of this secondary kprobe.
	* push_kprobe and pop_kprobe saves and restores
	* the currently active kprobe.
	*/
	kprobe_reenter_check(kcb, p);
	push_kprobe(kcb, p);
	kcb->kprobe_status = KPROBE_REENTER;
	} else {
	/*
	* If we have no pre-handler or it returned 0, we
	* continue with single stepping. If we have a
	* pre-handler and it returned non-zero, it prepped
	* for changing execution path, so get out doing
	* nothing more here.
	*/
	push_kprobe(kcb, p);
	kcb->kprobe_status = KPROBE_HIT_ACTIVE;
	if (p->pre_handler && p->pre_handler(p, regs)) {
	pop_kprobe(kcb);
	preempt_enable_no_resched();
	return 1;
	}
	kcb->kprobe_status = KPROBE_HIT_SS;
	}
	enable_singlestep(kcb, regs, (unsigned long) p->ainsn.insn);
	return 1;
	} /* else:
	* No kprobe at this address and no active kprobe. The trap has
	* not been caused by a kprobe breakpoint. The race of breakpoint
	* vs. kprobe remove does not exist because on s390 as we use
	* stop_machine to arm/disarm the breakpoints.
	*/
	preempt_enable_no_resched();
	return 0;
	}
	NOKPROBE_SYMBOL(kprobe_handler);

	/*
	* Called after single-stepping. p->addr is the address of the
	* instruction whose first byte has been replaced by the "breakpoint"
	* 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.
	*/
	static void resume_execution(struct kprobe p, struct pt_regs regs)
	{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	unsigned long ip = regs->psw.addr;
	int fixup = probe_get_fixup_type(p->ainsn.insn);

	if (fixup & FIXUP_PSW_NORMAL)
	ip += (unsigned long) p->addr - (unsigned long) p->ainsn.insn;

	if (fixup & FIXUP_BRANCH_NOT_TAKEN) {
	int ilen = insn_length(p->ainsn.insn[0] >> 8);
	if (ip - (unsigned long) p->ainsn.insn == ilen)
	ip = (unsigned long) p->addr + ilen;
	}

	if (fixup & FIXUP_RETURN_REGISTER) {
	int reg = (p->ainsn.insn[0] & 0xf0) >> 4;
	regs->gprs[reg] += (unsigned long) p->addr -
	(unsigned long) p->ainsn.insn;
	}

	disable_singlestep(kcb, regs, ip);
	}
	NOKPROBE_SYMBOL(resume_execution);

	static int post_kprobe_handler(struct pt_regs *regs)
	{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	struct kprobe *p = kprobe_running();

	if (!p)
	return 0;

	resume_execution(p, regs);
	if (kcb->kprobe_status != KPROBE_REENTER && p->post_handler) {
	kcb->kprobe_status = KPROBE_HIT_SSDONE;
	p->post_handler(p, regs, 0);
	}
	pop_kprobe(kcb);
	preempt_enable_no_resched();

	/*
	* if somebody else is singlestepping across a probe point, psw mask
	* will have PER set, in which case, continue the remaining processing
	* of do_single_step, as if this is not a probe hit.
	*/
	if (regs->psw.mask & PSW_MASK_PER)
	return 0;

	return 1;
	}
	NOKPROBE_SYMBOL(post_kprobe_handler);

	static int kprobe_trap_handler(struct pt_regs *regs, int trapnr)
	{
	struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
	struct kprobe *p = kprobe_running();

	switch(kcb->kprobe_status) {
	case KPROBE_HIT_SS:
	case KPROBE_REENTER:
	/*
	* We are here because the instruction being single
	* stepped caused a page fault. We reset the current
	* kprobe and the nip points back to the probe address
	* and allow the page fault handler to continue as a
	* normal page fault.
	*/
	disable_singlestep(kcb, regs, (unsigned long) p->addr);
	pop_kprobe(kcb);
	preempt_enable_no_resched();
	break;
	case KPROBE_HIT_ACTIVE:
	case KPROBE_HIT_SSDONE:
	/*
	* In case the user-specified fault handler returned
	* zero, try to fix up.
	*/
	if (fixup_exception(regs))
	return 1;
	/*
	* fixup_exception() could not handle it,
	* Let do_page_fault() fix it.
	*/
	break;
	default:
	break;
	}
	return 0;
	}
	NOKPROBE_SYMBOL(kprobe_trap_handler);

	int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
	{
	int ret;

	if (regs->psw.mask & (PSW_MASK_IO \| PSW_MASK_EXT))
	local_irq_disable();
	ret = kprobe_trap_handler(regs, trapnr);
	if (regs->psw.mask & (PSW_MASK_IO \| PSW_MASK_EXT))
	local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);
	return ret;
	}
	NOKPROBE_SYMBOL(kprobe_fault_handler);

	/*
	* Wrapper routine to for handling exceptions.
	*/
	int kprobe_exceptions_notify(struct notifier_block *self,
	unsigned long val, void *data)
	{
	struct die_args args = (struct die_args ) data;
	struct pt_regs *regs = args->regs;
	int ret = NOTIFY_DONE;

	if (regs->psw.mask & (PSW_MASK_IO \| PSW_MASK_EXT))
	local_irq_disable();

	switch (val) {
	case DIE_BPT:
	if (kprobe_handler(regs))
	ret = NOTIFY_STOP;
	break;
	case DIE_SSTEP:
	if (post_kprobe_handler(regs))
	ret = NOTIFY_STOP;
	break;
	case DIE_TRAP:
	if (!preemptible() && kprobe_running() &&
	kprobe_trap_handler(regs, args->trapnr))
	ret = NOTIFY_STOP;
	break;
	default:
	break;
	}

	if (regs->psw.mask & (PSW_MASK_IO \| PSW_MASK_EXT))
	local_irq_restore(regs->psw.mask & ~PSW_MASK_PER);

	return ret;
	}
	NOKPROBE_SYMBOL(kprobe_exceptions_notify);

	int __init arch_init_kprobes(void)
	{
	return 0;
	}

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