arch/powerpc/kernel/hw_breakpoint.c - arm/linux - Git at Google

 /*
  * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
  * using the CPU's debug registers. Derived from
  * "arch/x86/kernel/hw_breakpoint.c"
  *
  * 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 2010 IBM Corporation
  * Author: K.Prasad <prasad@linux.vnet.ibm.com>
  *
  */

 #include <linux/hw_breakpoint.h>
 #include <linux/notifier.h>
 #include <linux/kprobes.h>
 #include <linux/percpu.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
 #include <linux/smp.h>

 #include <asm/hw_breakpoint.h>
 #include <asm/processor.h>
 #include <asm/sstep.h>
 #include <linux/uaccess.h>

 /*
  * Stores the breakpoints currently in use on each breakpoint address
  * register for every cpu
  */
 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);

 /*
  * Returns total number of data or instruction breakpoints available.
  */
 int hw_breakpoint_slots(int type)
 {
 	if (type == TYPE_DATA)
 		return HBP_NUM;
 	return 0;		/* no instruction breakpoints available */
 }

 /*
  * Install a perf counter breakpoint.
  *
  * We seek a free debug address register and use it for this
  * breakpoint.
  *
  * Atomic: we hold the counter->ctx->lock and we only handle variables
  * and registers local to this cpu.
  */
 int arch_install_hw_breakpoint(struct perf_event *bp)
 {
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
 	struct perf_event **slot = this_cpu_ptr(&bp_per_reg);

 	*slot = bp;

 	/*
 	 * Do not install DABR values if the instruction must be single-stepped.
 	 * If so, DABR will be populated in single_step_dabr_instruction().
 	 */
 	if (current->thread.last_hit_ubp != bp)
 		__set_breakpoint(info);

 	return 0;
 }

 /*
  * Uninstall the breakpoint contained in the given counter.
  *
  * First we search the debug address register it uses and then we disable
  * it.
  *
  * Atomic: we hold the counter->ctx->lock and we only handle variables
  * and registers local to this cpu.
  */
 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
 {
 	struct perf_event **slot = this_cpu_ptr(&bp_per_reg);

 	if (*slot != bp) {
 		WARN_ONCE(1, "Can't find the breakpoint");
 		return;
 	}

 	*slot = NULL;
 	hw_breakpoint_disable();
 }

 /*
  * Perform cleanup of arch-specific counters during unregistration
  * of the perf-event
  */
 void arch_unregister_hw_breakpoint(struct perf_event *bp)
 {
 	/*
 	 * If the breakpoint is unregistered between a hw_breakpoint_handler()
 	 * and the single_step_dabr_instruction(), then cleanup the breakpoint
 	 * restoration variables to prevent dangling pointers.
 	 * FIXME, this should not be using bp->ctx at all! Sayeth peterz.
 	 */
 	if (bp->ctx && bp->ctx->task && bp->ctx->task != ((void *)-1L))
 		bp->ctx->task->thread.last_hit_ubp = NULL;
 }

 /*
  * Check for virtual address in kernel space.
  */
 int arch_check_bp_in_kernelspace(struct perf_event *bp)
 {
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

 	return is_kernel_addr(info->address);
 }

 int arch_bp_generic_fields(int type, int *gen_bp_type)
 {
 	*gen_bp_type = 0;
 	if (type & HW_BRK_TYPE_READ)
 		*gen_bp_type |= HW_BREAKPOINT_R;
 	if (type & HW_BRK_TYPE_WRITE)
 		*gen_bp_type |= HW_BREAKPOINT_W;
 	if (*gen_bp_type == 0)
 		return -EINVAL;
 	return 0;
 }

 /*
  * Validate the arch-specific HW Breakpoint register settings
  */
 int arch_validate_hwbkpt_settings(struct perf_event *bp)
 {
 	int ret = -EINVAL, length_max;
 	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

 	if (!bp)
 		return ret;

 	info->type = HW_BRK_TYPE_TRANSLATE;
 	if (bp->attr.bp_type & HW_BREAKPOINT_R)
 		info->type |= HW_BRK_TYPE_READ;
 	if (bp->attr.bp_type & HW_BREAKPOINT_W)
 		info->type |= HW_BRK_TYPE_WRITE;
 	if (info->type == HW_BRK_TYPE_TRANSLATE)
 		/* must set alteast read or write */
 		return ret;
 	if (!(bp->attr.exclude_user))
 		info->type |= HW_BRK_TYPE_USER;
 	if (!(bp->attr.exclude_kernel))
 		info->type |= HW_BRK_TYPE_KERNEL;
 	if (!(bp->attr.exclude_hv))
 		info->type |= HW_BRK_TYPE_HYP;
 	info->address = bp->attr.bp_addr;
 	info->len = bp->attr.bp_len;

 	/*
 	 * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
 	 * and breakpoint addresses are aligned to nearest double-word
 	 * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
 	 * 'symbolsize' should satisfy the check below.
 	 */
 	length_max = 8; /* DABR */
 	if (cpu_has_feature(CPU_FTR_DAWR)) {
 		length_max = 512 ; /* 64 doublewords */
 		/* DAWR region can't cross 512 boundary */
 		if ((bp->attr.bp_addr >> 10) !=
 		    ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
 			return -EINVAL;
 	}
 	if (info->len >
 	    (length_max - (info->address & HW_BREAKPOINT_ALIGN)))
 		return -EINVAL;
 	return 0;
 }

 /*
  * Restores the breakpoint on the debug registers.
  * Invoke this function if it is known that the execution context is
  * about to change to cause loss of MSR_SE settings.
  */
 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
 {
 	struct arch_hw_breakpoint *info;

 	if (likely(!tsk->thread.last_hit_ubp))
 		return;

 	info = counter_arch_bp(tsk->thread.last_hit_ubp);
 	regs->msr &= ~MSR_SE;
 	__set_breakpoint(info);
 	tsk->thread.last_hit_ubp = NULL;
 }

 /*
  * Handle debug exception notifications.
  */
 int hw_breakpoint_handler(struct die_args *args)
 {
 	int rc = NOTIFY_STOP;
 	struct perf_event *bp;
 	struct pt_regs *regs = args->regs;
 #ifndef CONFIG_PPC_8xx
 	int stepped = 1;
 	unsigned int instr;
 #endif
 	struct arch_hw_breakpoint *info;
 	unsigned long dar = regs->dar;

 	/* Disable breakpoints during exception handling */
 	hw_breakpoint_disable();

 	/*
 	 * The counter may be concurrently released but that can only
 	 * occur from a call_rcu() path. We can then safely fetch
 	 * the breakpoint, use its callback, touch its counter
 	 * while we are in an rcu_read_lock() path.
 	 */
 	rcu_read_lock();

 	bp = __this_cpu_read(bp_per_reg);
 	if (!bp) {
 		rc = NOTIFY_DONE;
 		goto out;
 	}
 	info = counter_arch_bp(bp);

 	/*
 	 * Return early after invoking user-callback function without restoring
 	 * DABR if the breakpoint is from ptrace which always operates in
 	 * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
 	 * generated in do_dabr().
 	 */
 	if (bp->overflow_handler == ptrace_triggered) {
 		perf_bp_event(bp, regs);
 		rc = NOTIFY_DONE;
 		goto out;
 	}

 	/*
 	 * Verify if dar lies within the address range occupied by the symbol
 	 * being watched to filter extraneous exceptions.  If it doesn't,
 	 * we still need to single-step the instruction, but we don't
 	 * generate an event.
 	 */
 	info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
 	if (!((bp->attr.bp_addr <= dar) &&
 	      (dar - bp->attr.bp_addr < bp->attr.bp_len)))
 		info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;

 #ifndef CONFIG_PPC_8xx
 	/* Do not emulate user-space instructions, instead single-step them */
 	if (user_mode(regs)) {
 		current->thread.last_hit_ubp = bp;
 		regs->msr |= MSR_SE;
 		goto out;
 	}

 	stepped = 0;
 	instr = 0;
 	if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
 		stepped = emulate_step(regs, instr);

 	/*
 	 * emulate_step() could not execute it. We've failed in reliably
 	 * handling the hw-breakpoint. Unregister it and throw a warning
 	 * message to let the user know about it.
 	 */
 	if (!stepped) {
 		WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
 			"0x%lx will be disabled.", info->address);
 		perf_event_disable_inatomic(bp);
 		goto out;
 	}
 #endif
 	/*
 	 * As a policy, the callback is invoked in a 'trigger-after-execute'
 	 * fashion
 	 */
 	if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
 		perf_bp_event(bp, regs);

 	__set_breakpoint(info);
 out:
 	rcu_read_unlock();
 	return rc;
 }
 NOKPROBE_SYMBOL(hw_breakpoint_handler);

 /*
  * Handle single-step exceptions following a DABR hit.
  */
 static int single_step_dabr_instruction(struct die_args *args)
 {
 	struct pt_regs *regs = args->regs;
 	struct perf_event *bp = NULL;
 	struct arch_hw_breakpoint *info;

 	bp = current->thread.last_hit_ubp;
 	/*
 	 * Check if we are single-stepping as a result of a
 	 * previous HW Breakpoint exception
 	 */
 	if (!bp)
 		return NOTIFY_DONE;

 	info = counter_arch_bp(bp);

 	/*
 	 * We shall invoke the user-defined callback function in the single
 	 * stepping handler to confirm to 'trigger-after-execute' semantics
 	 */
 	if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
 		perf_bp_event(bp, regs);

 	__set_breakpoint(info);
 	current->thread.last_hit_ubp = NULL;

 	/*
 	 * If the process was being single-stepped by ptrace, let the
 	 * other single-step actions occur (e.g. generate SIGTRAP).
 	 */
 	if (test_thread_flag(TIF_SINGLESTEP))
 		return NOTIFY_DONE;

 	return NOTIFY_STOP;
 }
 NOKPROBE_SYMBOL(single_step_dabr_instruction);

 /*
  * Handle debug exception notifications.
  */
 int hw_breakpoint_exceptions_notify(
 		struct notifier_block *unused, unsigned long val, void *data)
 {
 	int ret = NOTIFY_DONE;

 	switch (val) {
 	case DIE_DABR_MATCH:
 		ret = hw_breakpoint_handler(data);
 		break;
 	case DIE_SSTEP:
 		ret = single_step_dabr_instruction(data);
 		break;
 	}

 	return ret;
 }
 NOKPROBE_SYMBOL(hw_breakpoint_exceptions_notify);

 /*
  * Release the user breakpoints used by ptrace
  */
 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
 {
 	struct thread_struct *t = &tsk->thread;

 	unregister_hw_breakpoint(t->ptrace_bps[0]);
 	t->ptrace_bps[0] = NULL;
 }

 void hw_breakpoint_pmu_read(struct perf_event *bp)
 {
 	/* TODO */
 }
	/*
	* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
	* using the CPU's debug registers. Derived from
	* "arch/x86/kernel/hw_breakpoint.c"
	*
	* 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 2010 IBM Corporation
	* Author: K.Prasad <prasad@linux.vnet.ibm.com>
	*
	*/

	#include <linux/hw_breakpoint.h>
	#include <linux/notifier.h>
	#include <linux/kprobes.h>
	#include <linux/percpu.h>
	#include <linux/kernel.h>
	#include <linux/sched.h>
	#include <linux/smp.h>

	#include <asm/hw_breakpoint.h>
	#include <asm/processor.h>
	#include <asm/sstep.h>
	#include <linux/uaccess.h>

	/*
	* Stores the breakpoints currently in use on each breakpoint address
	* register for every cpu
	*/
	static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);

	/*
	* Returns total number of data or instruction breakpoints available.
	*/
	int hw_breakpoint_slots(int type)
	{
	if (type == TYPE_DATA)
	return HBP_NUM;
	return 0; /* no instruction breakpoints available */
	}

	/*
	* Install a perf counter breakpoint.
	*
	* We seek a free debug address register and use it for this
	* breakpoint.
	*
	* Atomic: we hold the counter->ctx->lock and we only handle variables
	* and registers local to this cpu.
	*/
	int arch_install_hw_breakpoint(struct perf_event *bp)
	{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);
	struct perf_event **slot = this_cpu_ptr(&bp_per_reg);

	*slot = bp;

	/*
	* Do not install DABR values if the instruction must be single-stepped.
	* If so, DABR will be populated in single_step_dabr_instruction().
	*/
	if (current->thread.last_hit_ubp != bp)
	__set_breakpoint(info);

	return 0;
	}

	/*
	* Uninstall the breakpoint contained in the given counter.
	*
	* First we search the debug address register it uses and then we disable
	* it.
	*
	* Atomic: we hold the counter->ctx->lock and we only handle variables
	* and registers local to this cpu.
	*/
	void arch_uninstall_hw_breakpoint(struct perf_event *bp)
	{
	struct perf_event **slot = this_cpu_ptr(&bp_per_reg);

	if (*slot != bp) {
	WARN_ONCE(1, "Can't find the breakpoint");
	return;
	}

	*slot = NULL;
	hw_breakpoint_disable();
	}

	/*
	* Perform cleanup of arch-specific counters during unregistration
	* of the perf-event
	*/
	void arch_unregister_hw_breakpoint(struct perf_event *bp)
	{
	/*
	* If the breakpoint is unregistered between a hw_breakpoint_handler()
	* and the single_step_dabr_instruction(), then cleanup the breakpoint
	* restoration variables to prevent dangling pointers.
	* FIXME, this should not be using bp->ctx at all! Sayeth peterz.
	*/
	if (bp->ctx && bp->ctx->task && bp->ctx->task != ((void *)-1L))
	bp->ctx->task->thread.last_hit_ubp = NULL;
	}

	/*
	* Check for virtual address in kernel space.
	*/
	int arch_check_bp_in_kernelspace(struct perf_event *bp)
	{
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

	return is_kernel_addr(info->address);
	}

	int arch_bp_generic_fields(int type, int *gen_bp_type)
	{
	*gen_bp_type = 0;
	if (type & HW_BRK_TYPE_READ)
	*gen_bp_type \|= HW_BREAKPOINT_R;
	if (type & HW_BRK_TYPE_WRITE)
	*gen_bp_type \|= HW_BREAKPOINT_W;
	if (*gen_bp_type == 0)
	return -EINVAL;
	return 0;
	}

	/*
	* Validate the arch-specific HW Breakpoint register settings
	*/
	int arch_validate_hwbkpt_settings(struct perf_event *bp)
	{
	int ret = -EINVAL, length_max;
	struct arch_hw_breakpoint *info = counter_arch_bp(bp);

	if (!bp)
	return ret;

	info->type = HW_BRK_TYPE_TRANSLATE;
	if (bp->attr.bp_type & HW_BREAKPOINT_R)
	info->type \|= HW_BRK_TYPE_READ;
	if (bp->attr.bp_type & HW_BREAKPOINT_W)
	info->type \|= HW_BRK_TYPE_WRITE;
	if (info->type == HW_BRK_TYPE_TRANSLATE)
	/* must set alteast read or write */
	return ret;
	if (!(bp->attr.exclude_user))
	info->type \|= HW_BRK_TYPE_USER;
	if (!(bp->attr.exclude_kernel))
	info->type \|= HW_BRK_TYPE_KERNEL;
	if (!(bp->attr.exclude_hv))
	info->type \|= HW_BRK_TYPE_HYP;
	info->address = bp->attr.bp_addr;
	info->len = bp->attr.bp_len;

	/*
	* Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
	* and breakpoint addresses are aligned to nearest double-word
	* HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
	* 'symbolsize' should satisfy the check below.
	*/
	length_max = 8; /* DABR */
	if (cpu_has_feature(CPU_FTR_DAWR)) {
	length_max = 512 ; /* 64 doublewords */
	/* DAWR region can't cross 512 boundary */
	if ((bp->attr.bp_addr >> 10) !=
	((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
	return -EINVAL;
	}
	if (info->len >
	(length_max - (info->address & HW_BREAKPOINT_ALIGN)))
	return -EINVAL;
	return 0;
	}

	/*
	* Restores the breakpoint on the debug registers.
	* Invoke this function if it is known that the execution context is
	* about to change to cause loss of MSR_SE settings.
	*/
	void thread_change_pc(struct task_struct tsk, struct pt_regs regs)
	{
	struct arch_hw_breakpoint *info;

	if (likely(!tsk->thread.last_hit_ubp))
	return;

	info = counter_arch_bp(tsk->thread.last_hit_ubp);
	regs->msr &= ~MSR_SE;
	__set_breakpoint(info);
	tsk->thread.last_hit_ubp = NULL;
	}

	/*
	* Handle debug exception notifications.
	*/
	int hw_breakpoint_handler(struct die_args *args)
	{
	int rc = NOTIFY_STOP;
	struct perf_event *bp;
	struct pt_regs *regs = args->regs;
	#ifndef CONFIG_PPC_8xx
	int stepped = 1;
	unsigned int instr;
	#endif
	struct arch_hw_breakpoint *info;
	unsigned long dar = regs->dar;

	/* Disable breakpoints during exception handling */
	hw_breakpoint_disable();

	/*
	* The counter may be concurrently released but that can only
	* occur from a call_rcu() path. We can then safely fetch
	* the breakpoint, use its callback, touch its counter
	* while we are in an rcu_read_lock() path.
	*/
	rcu_read_lock();

	bp = __this_cpu_read(bp_per_reg);
	if (!bp) {
	rc = NOTIFY_DONE;
	goto out;
	}
	info = counter_arch_bp(bp);

	/*
	* Return early after invoking user-callback function without restoring
	* DABR if the breakpoint is from ptrace which always operates in
	* one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
	* generated in do_dabr().
	*/
	if (bp->overflow_handler == ptrace_triggered) {
	perf_bp_event(bp, regs);
	rc = NOTIFY_DONE;
	goto out;
	}

	/*
	* Verify if dar lies within the address range occupied by the symbol
	* being watched to filter extraneous exceptions. If it doesn't,
	* we still need to single-step the instruction, but we don't
	* generate an event.
	*/
	info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
	if (!((bp->attr.bp_addr <= dar) &&
	(dar - bp->attr.bp_addr < bp->attr.bp_len)))
	info->type \|= HW_BRK_TYPE_EXTRANEOUS_IRQ;

	#ifndef CONFIG_PPC_8xx
	/* Do not emulate user-space instructions, instead single-step them */
	if (user_mode(regs)) {
	current->thread.last_hit_ubp = bp;
	regs->msr \|= MSR_SE;
	goto out;
	}

	stepped = 0;
	instr = 0;
	if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
	stepped = emulate_step(regs, instr);

	/*
	* emulate_step() could not execute it. We've failed in reliably
	* handling the hw-breakpoint. Unregister it and throw a warning
	* message to let the user know about it.
	*/
	if (!stepped) {
	WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
	"0x%lx will be disabled.", info->address);
	perf_event_disable_inatomic(bp);
	goto out;
	}
	#endif
	/*
	* As a policy, the callback is invoked in a 'trigger-after-execute'
	* fashion
	*/
	if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
	perf_bp_event(bp, regs);

	__set_breakpoint(info);
	out:
	rcu_read_unlock();
	return rc;
	}
	NOKPROBE_SYMBOL(hw_breakpoint_handler);

	/*
	* Handle single-step exceptions following a DABR hit.
	*/
	static int single_step_dabr_instruction(struct die_args *args)
	{
	struct pt_regs *regs = args->regs;
	struct perf_event *bp = NULL;
	struct arch_hw_breakpoint *info;

	bp = current->thread.last_hit_ubp;
	/*
	* Check if we are single-stepping as a result of a
	* previous HW Breakpoint exception
	*/
	if (!bp)
	return NOTIFY_DONE;

	info = counter_arch_bp(bp);

	/*
	* We shall invoke the user-defined callback function in the single
	* stepping handler to confirm to 'trigger-after-execute' semantics
	*/
	if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
	perf_bp_event(bp, regs);

	__set_breakpoint(info);
	current->thread.last_hit_ubp = NULL;

	/*
	* If the process was being single-stepped by ptrace, let the
	* other single-step actions occur (e.g. generate SIGTRAP).
	*/
	if (test_thread_flag(TIF_SINGLESTEP))
	return NOTIFY_DONE;

	return NOTIFY_STOP;
	}
	NOKPROBE_SYMBOL(single_step_dabr_instruction);

	/*
	* Handle debug exception notifications.
	*/
	int hw_breakpoint_exceptions_notify(
	struct notifier_block unused, unsigned long val, void data)
	{
	int ret = NOTIFY_DONE;

	switch (val) {
	case DIE_DABR_MATCH:
	ret = hw_breakpoint_handler(data);
	break;
	case DIE_SSTEP:
	ret = single_step_dabr_instruction(data);
	break;
	}

	return ret;
	}
	NOKPROBE_SYMBOL(hw_breakpoint_exceptions_notify);

	/*
	* Release the user breakpoints used by ptrace
	*/
	void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
	{
	struct thread_struct *t = &tsk->thread;

	unregister_hw_breakpoint(t->ptrace_bps[0]);
	t->ptrace_bps[0] = NULL;
	}

	void hw_breakpoint_pmu_read(struct perf_event *bp)
	{
	/* TODO */
	}