/*
* 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) 2007 Alan Stern
* Copyright (C) IBM Corporation, 2009
*/
/*
* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
* using the CPU's debug registers.
* This file contains the arch-independent routines.
*/
#include <linux/irqflags.h>
#include <linux/kallsyms.h>
#include <linux/notifier.h>
#include <linux/kprobes.h>
#include <linux/kdebug.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/percpu.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <asm/hw_breakpoint.h>
#include <asm/processor.h>
#ifdef CONFIG_X86
#include <asm/debugreg.h>
#endif
/*
* Spinlock that protects all (un)register operations over kernel/user-space
* breakpoint requests
*/
static DEFINE_SPINLOCK(hw_breakpoint_lock);
/* Array of kernel-space breakpoint structures */
struct hw_breakpoint *hbp_kernel[HBP_NUM];
/*
* Per-processor copy of hbp_kernel[]. Used only when hbp_kernel is being
* modified but we need the older copy to handle any hbp exceptions. It will
* sync with hbp_kernel[] value after updation is done through IPIs.
*/
DEFINE_PER_CPU(struct hw_breakpoint*, this_hbp_kernel[HBP_NUM]);
/*
* Kernel breakpoints grow downwards, starting from HBP_NUM
* 'hbp_kernel_pos' denotes lowest numbered breakpoint register occupied for
* kernel-space request. We will initialise it here and not in an __init
* routine because load_debug_registers(), which uses this variable can be
* called very early during CPU initialisation.
*/
unsigned int hbp_kernel_pos = HBP_NUM;
/*
* An array containing refcount of threads using a given bkpt register
* Accesses are synchronised by acquiring hw_breakpoint_lock
*/
unsigned int hbp_user_refcount[HBP_NUM];
/*
* Load the debug registers during startup of a CPU.
*/
void load_debug_registers(void)
{
unsigned long flags;
struct task_struct *tsk = current;
spin_lock_bh(&hw_breakpoint_lock);
/* Prevent IPIs for new kernel breakpoint updates */
local_irq_save(flags);
arch_update_kernel_hw_breakpoint(NULL);
local_irq_restore(flags);
if (test_tsk_thread_flag(tsk, TIF_DEBUG))
arch_install_thread_hw_breakpoint(tsk);
spin_unlock_bh(&hw_breakpoint_lock);
}
/*
* Erase all the hardware breakpoint info associated with a thread.
*
* If tsk != current then tsk must not be usable (for example, a
* child being cleaned up from a failed fork).
*/
void flush_thread_hw_breakpoint(struct task_struct *tsk)
{
int i;
struct thread_struct *thread = &(tsk->thread);
spin_lock_bh(&hw_breakpoint_lock);
/* The thread no longer has any breakpoints associated with it */
clear_tsk_thread_flag(tsk, TIF_DEBUG);
for (i = 0; i < HBP_NUM; i++) {
if (thread->hbp[i]) {
hbp_user_refcount[i]--;
kfree(thread->hbp[i]);
thread->hbp[i] = NULL;
}
}
arch_flush_thread_hw_breakpoint(tsk);
/* Actually uninstall the breakpoints if necessary */
if (tsk == current)
arch_uninstall_thread_hw_breakpoint();
spin_unlock_bh(&hw_breakpoint_lock);
}
/*
* Copy the hardware breakpoint info from a thread to its cloned child.
*/
int copy_thread_hw_breakpoint(struct task_struct *tsk,
struct task_struct *child, unsigned long clone_flags)
{
/*
* We will assume that breakpoint settings are not inherited
* and the child starts out with no debug registers set.
* But what about CLONE_PTRACE?
*/
clear_tsk_thread_flag(child, TIF_DEBUG);
/* We will call flush routine since the debugregs are not inherited */
arch_flush_thread_hw_breakpoint(child);
return 0;
}
static int __register_user_hw_breakpoint(int pos, struct task_struct *tsk,
struct hw_breakpoint *bp)
{
struct thread_struct *thread = &(tsk->thread);
int rc;
/* Do not overcommit. Fail if kernel has used the hbp registers */
if (pos >= hbp_kernel_pos)
return -ENOSPC;
rc = arch_validate_hwbkpt_settings(bp, tsk);
if (rc)
return rc;
thread->hbp[pos] = bp;
hbp_user_refcount[pos]++;
arch_update_user_hw_breakpoint(pos, tsk);
/*
* Does it need to be installed right now?
* Otherwise it will get installed the next time tsk runs
*/
if (tsk == current)
arch_install_thread_hw_breakpoint(tsk);
return rc;
}
/*
* Modify the address of a hbp register already in use by the task
* Do not invoke this in-lieu of a __unregister_user_hw_breakpoint()
*/
static int __modify_user_hw_breakpoint(int pos, struct task_struct *tsk,
struct hw_breakpoint *bp)
{
struct thread_struct *thread = &(tsk->thread);
if ((pos >= hbp_kernel_pos) || (arch_validate_hwbkpt_settings(bp, tsk)))
return -EINVAL;
if (thread->hbp[pos] == NULL)
return -EINVAL;
thread->hbp[pos] = bp;
/*
* 'pos' must be that of a hbp register already used by 'tsk'
* Otherwise arch_modify_user_hw_breakpoint() will fail
*/
arch_update_user_hw_breakpoint(pos, tsk);
if (tsk == current)
arch_install_thread_hw_breakpoint(tsk);
return 0;
}
static void __unregister_user_hw_breakpoint(int pos, struct task_struct *tsk)
{
hbp_user_refcount[pos]--;
tsk->thread.hbp[pos] = NULL;
arch_update_user_hw_breakpoint(pos, tsk);
if (tsk == current)
arch_install_thread_hw_breakpoint(tsk);
}
/**
* register_user_hw_breakpoint - register a hardware breakpoint for user space
* @tsk: pointer to 'task_struct' of the process to which the address belongs
* @bp: the breakpoint structure to register
*
* @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and
* @bp->triggered must be set properly before invocation
*
*/
int register_user_hw_breakpoint(struct task_struct *tsk,
struct hw_breakpoint *bp)
{
struct thread_struct *thread = &(tsk->thread);
int i, rc = -ENOSPC;
spin_lock_bh(&hw_breakpoint_lock);
for (i = 0; i < hbp_kernel_pos; i++) {
if (!thread->hbp[i]) {
rc = __register_user_hw_breakpoint(i, tsk, bp);
break;
}
}
if (!rc)
set_tsk_thread_flag(tsk, TIF_DEBUG);
spin_unlock_bh(&hw_breakpoint_lock);
return rc;
}
EXPORT_SYMBOL_GPL(register_user_hw_breakpoint);
/**
* modify_user_hw_breakpoint - modify a user-space hardware breakpoint
* @tsk: pointer to 'task_struct' of the process to which the address belongs
* @bp: the breakpoint structure to unregister
*
*/
int modify_user_hw_breakpoint(struct task_struct *tsk, struct hw_breakpoint *bp)
{
struct thread_struct *thread = &(tsk->thread);
int i, ret = -ENOENT;
spin_lock_bh(&hw_breakpoint_lock);
for (i = 0; i < hbp_kernel_pos; i++) {
if (bp == thread->hbp[i]) {
ret = __modify_user_hw_breakpoint(i, tsk, bp);
break;
}
}
spin_unlock_bh(&hw_breakpoint_lock);
return ret;
}
EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint);
/**
* unregister_user_hw_breakpoint - unregister a user-space hardware breakpoint
* @tsk: pointer to 'task_struct' of the process to which the address belongs
* @bp: the breakpoint structure to unregister
*
*/
void unregister_user_hw_breakpoint(struct task_struct *tsk,
struct hw_breakpoint *bp)
{
struct thread_struct *thread = &(tsk->thread);
int i, pos = -1, hbp_counter = 0;
spin_lock_bh(&hw_breakpoint_lock);
for (i = 0; i < hbp_kernel_pos; i++) {
if (thread->hbp[i])
hbp_counter++;
if (bp == thread->hbp[i])
pos = i;
}
if (pos >= 0) {
__unregister_user_hw_breakpoint(pos, tsk);
hbp_counter--;
}
if (!hbp_counter)
clear_tsk_thread_flag(tsk, TIF_DEBUG);
spin_unlock_bh(&hw_breakpoint_lock);
}
EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint);
/**
* register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
* @bp: the breakpoint structure to register
*
* @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and
* @bp->triggered must be set properly before invocation
*
*/
int register_kernel_hw_breakpoint(struct hw_breakpoint *bp)
{
int rc;
rc = arch_validate_hwbkpt_settings(bp, NULL);
if (rc)
return rc;
spin_lock_bh(&hw_breakpoint_lock);
rc = -ENOSPC;
/* Check if we are over-committing */
if ((hbp_kernel_pos > 0) && (!hbp_user_refcount[hbp_kernel_pos-1])) {
hbp_kernel_pos--;
hbp_kernel[hbp_kernel_pos] = bp;
on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1);
rc = 0;
}
spin_unlock_bh(&hw_breakpoint_lock);
return rc;
}
EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint);
/**
* unregister_kernel_hw_breakpoint - unregister a HW breakpoint for kernel space
* @bp: the breakpoint structure to unregister
*
* Uninstalls and unregisters @bp.
*/
void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp)
{
int i, j;
spin_lock_bh(&hw_breakpoint_lock);
/* Find the 'bp' in our list of breakpoints for kernel */
for (i = hbp_kernel_pos; i < HBP_NUM; i++)
if (bp == hbp_kernel[i])
break;
/* Check if we did not find a match for 'bp'. If so return early */
if (i == HBP_NUM) {
spin_unlock_bh(&hw_breakpoint_lock);
return;
}
/*
* We'll shift the breakpoints one-level above to compact if
* unregistration creates a hole
*/
for (j = i; j > hbp_kernel_pos; j--)
hbp_kernel[j] = hbp_kernel[j-1];
hbp_kernel[hbp_kernel_pos] = NULL;
on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1);
hbp_kernel_pos++;
spin_unlock_bh(&hw_breakpoint_lock);
}
EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);
static struct notifier_block hw_breakpoint_exceptions_nb = {
.notifier_call = hw_breakpoint_exceptions_notify,
/* we need to be notified first */
.priority = 0x7fffffff
};
static int __init init_hw_breakpoint(void)
{
return register_die_notifier(&hw_breakpoint_exceptions_nb);
}
core_initcall(init_hw_breakpoint);
