Hardware Breakpoint interfaces - v2

Index: linux-HBKPT-2.6.28-rc7/include/asm-generic/hw_breakpoint.h
===================================================================
@@ -0,0 +1,241 @@
+#ifndef	_ASM_GENERIC_HW_BREAKPOINT_H
+#define	_ASM_GENERIC_HW_BREAKPOINT_H
+
+#ifndef __ARCH_HW_BREAKPOINT_H
+#error "Please don't include this file directly"
+#endif
+
+#ifdef	__KERNEL__
+#include <linux/list.h>
+#include <linux/types.h>
+
+/**
+ * struct hw_breakpoint - unified kernel/user-space hardware breakpoint
+ * @node: internal linked-list management
+ * @triggered: callback invoked after target address access
+ * @installed: callback invoked when the breakpoint is installed
+ * @uninstalled: callback invoked when the breakpoint is uninstalled
+ * @info: arch-specific breakpoint info (address, length, and type)
+ * @priority: requested priority level
+ * @status: current registration/installation status
+ *
+ * %hw_breakpoint structures are the kernel's way of representing
+ * hardware breakpoints.  These are data breakpoints
+ * (also known as "watchpoints", triggered on data access), and the breakpoint's
+ * target address can be located in either kernel space or user space.
+ *
+ * The breakpoint's address, length, and type are highly
+ * architecture-specific.  The values are encoded in the @info field; you
+ * specify them when registering the breakpoint.  To examine the encoded
+ * values use hw_breakpoint_get_{kaddress,uaddress,len,type}(), declared
+ * below.
+ *
+ * The address is specified as a regular kernel pointer (for kernel-space
+ * breakponts) or as an %__user pointer (for user-space breakpoints).
+ * With register_user_hw_breakpoint(), the address must refer to a
+ * location in user space.  The breakpoint will be active only while the
+ * requested task is running.  Conversely with
+ * register_kernel_hw_breakpoint(), the address must refer to a location
+ * in kernel space, and the breakpoint will be active on all CPUs
+ * regardless of the current task.
+ *
+ * The length is the breakpoint's extent in bytes, which is subject to
+ * certain limitations.  include/asm/hw_breakpoint.h contains macros
+ * defining the available lengths for a specific architecture.  Note that
+ * the address's alignment must match the length.  The breakpoint will
+ * catch accesses to any byte in the range from address to address +
+ * (length - 1).
+ *
+ * The breakpoint's type indicates the sort of access that will cause it
+ * to trigger.  Possible values may include:
+ *
+ * 	%HW_BREAKPOINT_RW (triggered on read or write access),
+ * 	%HW_BREAKPOINT_WRITE (triggered on write access), and
+ * 	%HW_BREAKPOINT_READ (triggered on read access).
+ *
+ * Appropriate macros are defined in include/asm/hw_breakpoint.h; not all
+ * possibilities are available on all architectures.  Execute breakpoints
+ * must have length equal to the special value %HW_BREAKPOINT_LEN_EXECUTE.
+ *
+ * When a breakpoint gets hit, the @pre_handler or @post_handler (whichever or
+ * both depending upon architecture support and assignment by user) callback is
+ * invoked in_interrupt with a pointer to the %hw_breakpoint structure and the
+ * processor registers.
+ * Data breakpoints occur after the memory access has taken place.
+ * Breakpoints are disabled during execution @triggered, to avoid
+ * recursive traps and allow unhindered access to breakpointed memory.
+ *
+ * Hardware breakpoints are implemented using the CPU's debug registers,
+ * which are a limited hardware resource.  Requests to register a
+ * breakpoint will always succeed provided the parameters are valid,
+ * but the breakpoint may not be installed in a debug register right
+ * away.  Physical debug registers are allocated based on the priority
+ * level stored in @priority (higher values indicate higher priority).
+ * User-space breakpoints within a single thread compete with one
+ * another, and all user-space breakpoints compete with all kernel-space
+ * breakpoints; however user-space breakpoints in different threads do
+ * not compete.  %HW_BREAKPOINT_PRIO_PTRACE is the level used for ptrace
+ * requests; an unobtrusive kernel-space breakpoint will use
+ * %HW_BREAKPOINT_PRIO_NORMAL to avoid disturbing user programs.  A
+ * kernel-space breakpoint that always wants to be installed and doesn't
+ * care about disrupting user debugging sessions can specify
+ * %HW_BREAKPOINT_PRIO_HIGH.
+ *
+ * A particular breakpoint may be allocated (installed in) a debug
+ * register or deallocated (uninstalled) from its debug register at any
+ * time, as other breakpoints are registered and unregistered.  The
+ * @installed and @uninstalled callbacks are invoked in_atomic when these
+ * events occur.  It is legal for @installed or @uninstalled to be %NULL,
+ * but one of the handlers - @pre_handler or @post_handler must be populated
+ * (please check support for your architecture using pre_ and
+ * post_handler_supported() routines to check for support.  Note that it is not
+ * possible to register or unregister a user-space breakpoint from within a
+ * callback routine, since doing so requires a process context.  Note that for
+ * user breakpoints, while in @installed and @uninstalled the thread may be
+ * context switched. Hence it may not be safe to call printk().
+ *
+ * For kernel-space breakpoints, @installed is invoked after the
+ * breakpoint is actually installed and @uninstalled is invoked before
+ * the breakpoint is actually uninstalled.  As a result the @pre_ and
+ * @post_handler() routines may be invoked when not expected, but this way you
+ * will know that during the time interval from @installed to @uninstalled, all
+ * events are faithfully reported.  (It is not possible to do any better than
+ * this in general, because on SMP systems there is no way to set a debug
+ * register simultaneously on all CPUs.)  The same isn't always true with
+ * user-space breakpoints, but the differences should not be visible to a
+ * user process.
+ *
+ * If you need to know whether your kernel-space breakpoint was installed
+ * immediately upon registration, you can check the return value from
+ * register_kernel_hw_breakpoint().  If the value is not > 0, you can
+ * give up and unregister the breakpoint right away.
+ *
+ * @node and @status are intended for internal use.  However @status
+ * may be read to determine whether or not the breakpoint is currently
+ * installed.  (The value is not reliable unless local interrupts are
+ * disabled.)
+ *
+ * This sample code sets a breakpoint on pid_max and registers a callback
+ * function for writes to that variable.  Note that it is not portable
+ * as written, because not all architectures support HW_BREAKPOINT_LEN_4.
+ *
+ * ----------------------------------------------------------------------
+ *
+ * #include <asm/hw_breakpoint.h>
+ *
+ * static void my_pre_handler(struct hw_breakpoint *bp, struct pt_regs *regs)
+ * {
+ * 	printk(KERN_DEBUG "Inside pre_handler of breakpoint exception\n");
+ * 	dump_stack();
+ *  	.......<more debugging output>........
+ * }
+ *
+ * static void my_post_handler(struct hw_breakpoint *bp, struct pt_regs *regs)
+ * {
+ * 	printk(KERN_DEBUG "Inside post_handler of breakpoint exception\n");
+ * 	dump_stack();
+ *  	.......<more debugging output>........
+ * }
+ *
+ * static struct hw_breakpoint my_bp;
+ *
+ * static int init_module(void)
+ * {
+ *	..........<do anything>............
+ *	int bkpt_type = HW_BREAKPOINT_WRITE;
+ *
+ *	if (pre_handler_supported(bkpt_type)
+ *		my_bp.pre_handler = my_pre_handler;
+ *	if (post_handler_supported(bkpt_type)
+ *		my_bp.post_handler = my_post_handler;
+ *	my_bp.priority = HW_BREAKPOINT_PRIO_NORMAL;
+ *	rc = register_kernel_hw_breakpoint(&my_bp, &pid_max,
+ *			HW_BREAKPOINT_LEN_4, bkpt_type);
+ *	..........<do anything>............
+ * }
+ *
+ * static void cleanup_module(void)
+ * {
+ *	..........<do anything>............
+ *	unregister_kernel_hw_breakpoint(&my_bp);
+ *	..........<do anything>............
+ * }
+ *
+ * ----------------------------------------------------------------------
+ *
+ */
+struct hw_breakpoint {
+	struct list_head	node;
+	void		(*installed)(struct hw_breakpoint *);
+	void		(*uninstalled)(struct hw_breakpoint *);
+	void		(*triggered)(struct hw_breakpoint *,
+							struct pt_regs *);
+	struct arch_hw_breakpoint	info;
+	u8		priority;
+	u8		status;
+};
+
+/*
+ * Inline accessor routines to retrieve the arch-specific parts of
+ * a breakpoint structure:
+ */
+static const void *hw_breakpoint_get_kaddress(struct hw_breakpoint *bp);
+static const void __user *hw_breakpoint_get_uaddress(struct hw_breakpoint *bp);
+static unsigned hw_breakpoint_get_len(struct hw_breakpoint *bp);
+static unsigned hw_breakpoint_get_type(struct hw_breakpoint *bp);
+
+/*
+ * len and type values are defined in include/asm/hw_breakpoint.h.
+ * Available values vary according to the architecture.  On i386 the
+ * possibilities are:
+ *
+ *	HW_BREAKPOINT_LEN_1
+ *	HW_BREAKPOINT_LEN_2
+ *	HW_BREAKPOINT_LEN_4
+ *	HW_BREAKPOINT_LEN_EXECUTE
+ *	HW_BREAKPOINT_RW
+ *	HW_BREAKPOINT_READ
+ *	HW_BREAKPOINT_EXECUTE
+ *
+ * On other architectures HW_BREAKPOINT_LEN_8 may be available, and the
+ * 1-, 2-, and 4-byte lengths may be unavailable.  There also may be
+ * HW_BREAKPOINT_WRITE.  You can use #ifdef to check at compile time.
+ */
+
+/* Standard HW breakpoint priority levels (higher value = higher priority) */
+#define HW_BREAKPOINT_PRIO_NORMAL	25
+#define HW_BREAKPOINT_PRIO_PTRACE	50
+#define HW_BREAKPOINT_PRIO_HIGH		75
+
+/* HW breakpoint status values (0 = not registered) */
+#define HW_BREAKPOINT_REGISTERED	1
+#define HW_BREAKPOINT_INSTALLED		2
+
+static DEFINE_MUTEX(hw_breakpoint_mutex);	/* Protects everything */
+
+/*
+ * The following two routines are meant to be called only from within
+ * the ptrace or utrace subsystems.  The tsk argument will usually be a
+ * process being debugged by the current task, although it is also legal
+ * for tsk to be the current task.  In any case it must be guaranteed
+ * that tsk will not start running in user mode while its breakpoints are
+ * being modified.
+ */
+int register_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp,
+		const void __user *address, unsigned len, unsigned type);
+void unregister_user_hw_breakpoint(struct task_struct *tsk,
+		struct hw_breakpoint *bp);
+
+/*
+ * Kernel breakpoints are not associated with any particular thread.
+ */
+int register_kernel_hw_breakpoint(struct hw_breakpoint *bp,
+		const void *address, unsigned len, unsigned type);
+void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);
+
+struct thread_hw_breakpoint *alloc_thread_hw_breakpoint(
+						struct task_struct *tsk);
+
+#endif	/* __KERNEL__ */
+#endif	/* _ASM_GENERIC_HW_BREAKPOINT_H */

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Index: linux-HBKPT-2.6.28-rc7/arch/x86/kernel/hw_breakpoint.c
===================================================================
@@ -0,0 +1,441 @@
+/*
+ * 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) 2008 IBM Corporation
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+
+#include <linux/init.h>
+#include <linux/irqflags.h>
+#include <linux/kdebug.h>
+#include <linux/kernel.h>
+#include <linux/kprobes.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/notifier.h>
+#include <linux/rculist.h>
+#include <linux/sched.h>
+#include <linux/smp.h>
+#include <linux/percpu.h>
+
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
+#include <asm/processor.h>
+
+/* Arch-specific hook routines */
+
+/*
+ * Install the kernel breakpoints in their debug registers.
+ */
+static void arch_install_chbi(struct cpu_hw_breakpoint *chbi)
+{
+	struct hw_breakpoint **bps;
+
+	/* Don't allow debug exceptions while we update the registers */
+	set_debugreg(0UL, 7);
+	chbi->cur_kbpdata = rcu_dereference(cur_kbpdata);
+
+	/* Kernel breakpoints are stored starting in DR0 and going up */
+	bps = chbi->cur_kbpdata->bps;
+	switch (chbi->cur_kbpdata->num_kbps) {
+	case 4:
+		set_debugreg(bps[3]->info.address, 3);
+	case 3:
+		set_debugreg(bps[2]->info.address, 2);
+	case 2:
+		set_debugreg(bps[1]->info.address, 1);
+	case 1:
+		set_debugreg(bps[0]->info.address, 0);
+	}
+	/* No need to set DR6 */
+	set_debugreg(chbi->cur_kbpdata->mkdr7, 7);
+}
+
+/*
+ * Update an out-of-date thread hw_breakpoint info structure.
+ */
+static void arch_update_thbi(struct thread_hw_breakpoint *thbi,
+		struct kernel_bp_data *thr_kbpdata)
+{
+	int num = thr_kbpdata->num_kbps;
+
+	thbi->tkdr7 = thr_kbpdata->mkdr7 | (thbi->tdr7 & ~kdr7_masks[num]);
+}
+
+/*
+ * Install the thread breakpoints in their debug registers.
+ */
+static void arch_install_thbi(struct thread_hw_breakpoint *thbi)
+{
+	/* Install the user breakpoints.  Kernel breakpoints are stored
+	 * starting in DR0 and going up; there are num_kbps of them.
+	 * User breakpoints are stored starting in DR3 and going down,
+	 * as many as we have room for.
+	 */
+	switch (thbi->num_installed) {
+	case 4:
+		set_debugreg(thbi->tdr[0], 0);
+	case 3:
+		set_debugreg(thbi->tdr[1], 1);
+	case 2:
+		set_debugreg(thbi->tdr[2], 2);
+	case 1:
+		set_debugreg(thbi->tdr[3], 3);
+	}
+	/* No need to set DR6 */
+	set_debugreg(thbi->tkdr7, 7);
+}
+
+/*
+ * Install the debug register values for just the kernel, no thread.
+ */
+static void arch_install_none(struct cpu_hw_breakpoint *chbi)
+{
+	set_debugreg(chbi->cur_kbpdata->mkdr7, 7);
+}
+
+/*
+ * Create a new kbpdata entry.
+ */
+static void arch_new_kbpdata(struct kernel_bp_data *new_kbpdata)
+{
+	int num = new_kbpdata->num_kbps;
+
+	new_kbpdata->mkdr7 = kdr7 & (kdr7_masks[num] | DR_GLOBAL_SLOWDOWN);
+}
+
+/*
+ * Store a thread breakpoint array entry's address
+ */
+static void arch_store_thread_bp_array(struct thread_hw_breakpoint *thbi,
+		struct hw_breakpoint *bp, int i)
+{
+	thbi->tdr[i] = bp->info.address;
+}
+
+/*
+ * Store a breakpoint's encoded address, length, and type.
+ */
+static void arch_store_info(struct hw_breakpoint *bp,
+		unsigned long address, unsigned len, unsigned type)
+{
+	bp->info.address = address;
+	bp->info.len = len;
+	bp->info.type = type;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+static int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
+			unsigned long address, unsigned len, unsigned int type,
+			unsigned int *align)
+{
+	int ret = -EINVAL;
+
+	switch (type) {
+	case HW_BREAKPOINT_WRITE:
+				break;
+	case HW_BREAKPOINT_RW:
+				break;
+	default:
+		return ret;
+	}
+
+	switch (len) {
+	case HW_BREAKPOINT_LEN_1:
+		*align = 0;
+		break;
+	case HW_BREAKPOINT_LEN_2:
+		*align = 1;
+		break;
+	case HW_BREAKPOINT_LEN_4:
+		*align = 3;
+		break;
+	default:
+		return ret;
+	}
+
+	if (bp->triggered) {
+		ret = 0;
+		arch_store_info(bp, address, len, type);
+	}
+	return ret;
+}
+
+/*
+ * Check for virtual address in user space.
+ */
+static int arch_check_va_in_userspace(unsigned long va,
+		struct task_struct *tsk)
+{
+#ifndef	CONFIG_X86_64
+#define	TASK_SIZE_OF(t)	TASK_SIZE
+#endif
+	return (va < TASK_SIZE_OF(tsk));
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+static int arch_check_va_in_kernelspace(unsigned long va)
+{
+#ifndef	CONFIG_X86_64
+#define	TASK_SIZE64	TASK_SIZE
+#endif
+	return (va >= TASK_SIZE64);
+}
+
+/*
+ * Encode the length, type, Exact, and Enable bits for a particular breakpoint
+ * as stored in debug register 7.
+ */
+static unsigned long encode_dr7(int drnum, unsigned len, unsigned type)
+{
+	unsigned long temp;
+
+	temp = (len | type) & 0xf;
+	temp <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
+	temp |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE)) |
+				DR_GLOBAL_SLOWDOWN;
+	return temp;
+}
+
+/*
+ * Calculate the DR7 value for a list of kernel or user breakpoints.
+ */
+static unsigned long calculate_dr7(struct thread_hw_breakpoint *thbi)
+{
+	int is_user;
+	struct list_head *bp_list;
+	struct hw_breakpoint *bp;
+	int i;
+	int drnum;
+	unsigned long dr7;
+
+	if (thbi) {
+		is_user = 1;
+		bp_list = &thbi->thread_bps;
+		drnum = HB_NUM - 1;
+	} else {
+		is_user = 0;
+		bp_list = &kernel_bps;
+		drnum = 0;
+	}
+
+	/* Kernel bps are assigned from DR0 on up, and user bps are assigned
+	 * from DR3 on down.  Accumulate all 4 bps; the kernel DR7 mask will
+	 * select the appropriate bits later.
+	 */
+	dr7 = 0;
+	i = 0;
+	list_for_each_entry(bp, bp_list, node) {
+
+		/* Get the debug register number and accumulate the bits */
+		dr7 |= encode_dr7(drnum, bp->info.len, bp->info.type);
+		if (++i >= HB_NUM)
+			break;
+		if (is_user)
+			--drnum;
+		else
+			++drnum;
+	}
+	return dr7;
+}
+
+/*
+ * Register a new user breakpoint structure.
+ */
+static void arch_register_user_hw_breakpoint(struct hw_breakpoint *bp,
+		struct thread_hw_breakpoint *thbi)
+{
+	thbi->tdr7 = calculate_dr7(thbi);
+
+	/* If this is an execution breakpoint for the current PC address,
+	 * we should clear the task's RF so that the bp will be certain
+	 * to trigger.
+	 *
+	 * FIXME: It's not so easy to get hold of the task's PC as a linear
+	 * address!  ptrace.c does this already...
+	 */
+}
+
+/*
+ * Unregister a user breakpoint structure.
+ */
+static void arch_unregister_user_hw_breakpoint(struct hw_breakpoint *bp,
+		struct thread_hw_breakpoint *thbi)
+{
+	thbi->tdr7 = calculate_dr7(thbi);
+}
+
+/*
+ * Register a kernel breakpoint structure.
+ */
+static void arch_register_kernel_hw_breakpoint(
+		struct hw_breakpoint *bp)
+{
+	kdr7 = calculate_dr7(NULL);
+}
+
+/*
+ * Unregister a kernel breakpoint structure.
+ */
+static void arch_unregister_kernel_hw_breakpoint(
+		struct hw_breakpoint *bp)
+{
+	kdr7 = calculate_dr7(NULL);
+}
+
+
+/* End of arch-specific hook routines */
+
+
+/*
+ * Copy out the debug register information for a core dump.
+ *
+ * tsk must be equal to current.
+ */
+void dump_thread_hw_breakpoint(struct task_struct *tsk, int u_debugreg[8])
+{
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+	int i;
+
+	memset(u_debugreg, 0, sizeof u_debugreg);
+	if (thbi) {
+		for (i = 0; i < HB_NUM; ++i)
+			u_debugreg[i] = thbi->vdr_bps[i].info.address;
+		u_debugreg[7] = thbi->vdr7;
+	}
+	u_debugreg[6] = tsk->thread.vdr6;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+
+static void switch_to_none_hw_breakpoint(void);
+static struct hw_breakpoint *last_hit_bp;
+static struct thread_hw_breakpoint *last_hit_thbi;
+
+static int __kprobes hw_breakpoint_handler(struct die_args *args)
+{
+	struct cpu_hw_breakpoint *chbi;
+	int i;
+	struct hw_breakpoint *bp;
+	struct thread_hw_breakpoint *thbi = NULL;
+
+	/* The DR6 value is stored in args->err */
+#define DR6	(args->err)
+
+	if (DR6 & DR_STEP)
+		return NOTIFY_DONE;
+
+	chbi = &per_cpu(cpu_info, get_cpu());
+
+	/* Disable all breakpoints so that the callbacks can run without
+	 * triggering recursive debug exceptions.
+	 */
+	set_debugreg(0UL, 7);
+
+	/* Assert that local interrupts are disabled */
+	/* Reset the DRn bits in the virtualized register value.
+	 * The ptrace trigger routine will add in whatever is needed.
+	 */
+	current->thread.vdr6 &= ~(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3);
+
+	/* Are we a victim of lazy debug-register switching? */
+	if (!chbi->bp_task)
+		;
+	else if (chbi->bp_task != current) {
+
+		/* No user breakpoints are valid.  Perform the belated
+		 * debug-register switch.
+		 */
+		switch_to_none_hw_breakpoint();
+	} else {
+		thbi = chbi->bp_task->thread.hw_breakpoint_info;
+	}
+
+	/* Handle all the breakpoints that were triggered */
+	for (i = 0; i < HB_NUM; ++i) {
+		if (likely(!(DR6 & (DR_TRAP0 << i))))
+			continue;
+
+		/* Find the corresponding hw_breakpoint structure and
+		 * invoke its triggered callback.
+		 */
+		if (i < chbi->cur_kbpdata->num_kbps)
+			bp = chbi->cur_kbpdata->bps[i];
+		else if (thbi)
+			bp = thbi->bps[i];
+		else		/* False alarm due to lazy DR switching */
+			continue;
+		if (bp) {
+			switch (bp->info.type) {
+			case HW_BREAKPOINT_WRITE:
+			case HW_BREAKPOINT_RW:
+				if (bp->triggered)
+					(bp->triggered)(bp, args->regs);
+				/* Re-enable the breakpoints */
+				set_debugreg(thbi ? thbi->tkdr7 :
+						chbi->cur_kbpdata->mkdr7, 7);
+				put_cpu_no_resched();
+
+				return NOTIFY_STOP;
+			}
+		}
+	}
+	/* Stop processing further if the exception is a stray one */
+	if (!(DR6 & ~(DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)))
+		return NOTIFY_STOP;
+
+	return NOTIFY_DONE;
+#undef DR6
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+static int __kprobes hw_breakpoint_exceptions_notify(
+		struct notifier_block *unused, unsigned long val, void *data)
+{
+	if (val != DIE_DEBUG)
+		return NOTIFY_DONE;
+	return hw_breakpoint_handler(data);
+}
+
+static struct notifier_block hw_breakpoint_exceptions_nb = {
+	.notifier_call = hw_breakpoint_exceptions_notify,
+	.priority = 0x7fffffff /* we need to be notified first */
+};
+
+static int __init init_hw_breakpoint(void)
+{
+	load_debug_registers();
+	return register_die_notifier(&hw_breakpoint_exceptions_nb);
+}
+
+core_initcall(init_hw_breakpoint);
+
+
+/* Grab the arch-independent code */
+#include "../../../kernel/hw_breakpoint.c"
+

128 lines not on this page · raw message

Index: linux-HBKPT-2.6.28-rc7/arch/x86/kernel/traps.c
===================================================================
@@ -573,10 +573,11 @@ asmlinkage __kprobes struct pt_regs *syn
 dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 {
 	struct task_struct *tsk = current;
-	unsigned long condition;
+	unsigned long dr6;
 	int si_code;
 
-	get_debugreg(condition, 6);
+	get_debugreg(dr6, 6);
+	set_debugreg(0, 6);	/* DR6 may or may not be cleared by the CPU */
 
 	/*
 	 * The processor cleared BTF, so don't mark that we need it set.

@@ -584,61 +585,40 @@ dotraplinkage void __kprobes do_debug(st
 	clear_tsk_thread_flag(tsk, TIF_DEBUGCTLMSR);
 	tsk->thread.debugctlmsr = 0;
 
-	if (notify_die(DIE_DEBUG, "debug", regs, condition, error_code,
+	/* Store the virtualized DR6 value */
+	tsk->thread.vdr6 = dr6;
+
+	if (notify_die(DIE_DEBUG, "debug", regs, dr6, error_code,
 						SIGTRAP) == NOTIFY_STOP)
 		return;
 
 	/* It's safe to allow irq's after DR6 has been saved */
 	preempt_conditional_sti(regs);
 
-	/* Mask out spurious debug traps due to lazy DR7 setting */
-	if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {
-		if (!tsk->thread.debugreg7)
-			goto clear_dr7;
+	if (regs->flags & X86_VM_MASK) {
+		handle_vm86_trap((struct kernel_vm86_regs *) regs,
+				error_code, 1);
+		return;
 	}
 
 #ifdef CONFIG_X86_32
-	if (regs->flags & X86_VM_MASK)
-		goto debug_vm86;
 #endif
 
-	/* Save debug status register where ptrace can see it */
-	tsk->thread.debugreg6 = condition;
-
-	/*
-	 * Single-stepping through TF: make sure we ignore any events in
-	 * kernel space (but re-enable TF when returning to user mode).
-	 */
-	if (condition & DR_STEP) {
-		if (!user_mode(regs))
-			goto clear_TF_reenable;
-	}
-
-	si_code = get_si_code(condition);
-	/* Ok, finally something we can handle */
-	send_sigtrap(tsk, regs, error_code, si_code);
-
 	/*
-	 * Disable additional traps. They'll be re-enabled when
-	 * the signal is delivered.
+	 * Single-stepping through system calls: ignore any exceptions in
+	 * kernel space, but re-enable TF when returning to user mode.
+	 *
+	 * We already checked v86 mode above, so we can check for kernel mode
+	 * by just checking the CPL of CS.
 	 */
-clear_dr7:
-	set_debugreg(0, 7);
-	preempt_conditional_cli(regs);
-	return;
-
-#ifdef CONFIG_X86_32
-debug_vm86:
-	handle_vm86_trap((struct kernel_vm86_regs *) regs, error_code, 1);
-	preempt_conditional_cli(regs);
-	return;
-#endif
-
-clear_TF_reenable:
-	set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
-	regs->flags &= ~X86_EFLAGS_TF;
-	preempt_conditional_cli(regs);
-	return;
+	if ((dr6 & DR_STEP) && !user_mode(regs)) {
+		tsk->thread.vdr6 &= ~DR_STEP;
+		set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
+		regs->flags &= ~X86_EFLAGS_TF;
+	}
+	si_code = get_si_code(dr6);
+	if (tsk->thread.vdr6 & (DR_STEP|DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3))
+		send_sigtrap(tsk, regs, error_code, si_code);
 }
 
 #ifdef CONFIG_X86_64

Index: linux-HBKPT-2.6.28-rc7/arch/x86/kernel/kprobes.c
===================================================================
@@ -54,6 +54,7 @@
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
 #include <asm/alternative.h>
+#include <asm/debugreg.h>
 
 void jprobe_return_end(void);
 

@@ -517,6 +518,7 @@ static int __kprobes kprobe_handler(stru
 	kprobe_opcode_t *addr;
 	struct kprobe *p;
 	struct kprobe_ctlblk *kcb;
+	unsigned int *ssr;
 
 	addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
 	if (*addr != BREAKPOINT_INSTRUCTION) {

@@ -962,6 +964,10 @@ int __kprobes kprobe_exceptions_notify(s
 			ret = NOTIFY_STOP;
 		break;
 	case DIE_DEBUG:
+		/* We could be here due to single-stepping after a pre-handler
+		 * execution of HW Breakpoint or kprobes. We determine the cause
+		 * using the bitmask flag 'sstep_reason'.
+		 */
 		if (post_kprobe_handler(args->regs))
 			ret = NOTIFY_STOP;
 		break;

Index: linux-HBKPT-2.6.28-rc7/arch/x86/include/asm/debugreg.h
===================================================================
@@ -49,6 +49,8 @@
 
 #define DR_LOCAL_ENABLE_SHIFT 0    /* Extra shift to the local enable bit */
 #define DR_GLOBAL_ENABLE_SHIFT 1   /* Extra shift to the global enable bit */
+#define DR_LOCAL_ENABLE (0x1)      /* Local enable for reg 0 */
+#define DR_GLOBAL_ENABLE (0x2)     /* Global enable for reg 0 */
 #define DR_ENABLE_SIZE 2           /* 2 enable bits per register */
 
 #define DR_LOCAL_ENABLE_MASK (0x55)  /* Set  local bits for all 4 regs */

@@ -67,4 +69,31 @@
 #define DR_LOCAL_SLOWDOWN (0x100)   /* Local slow the pipeline */
 #define DR_GLOBAL_SLOWDOWN (0x200)  /* Global slow the pipeline */
 
+/*
+ * HW breakpoint additions
+ */
+#ifdef __KERNEL__
+
+#define HB_NUM		4	/* Number of hardware breakpoints */
+
+/* For process management */
+void flush_thread_hw_breakpoint(struct task_struct *tsk);
+int copy_thread_hw_breakpoint(struct task_struct *tsk,
+		struct task_struct *child, unsigned long clone_flags);
+void dump_thread_hw_breakpoint(struct task_struct *tsk, int u_debugreg[8]);
+void switch_to_thread_hw_breakpoint(struct task_struct *tsk);
+
+/* For CPU management */
+void load_debug_registers(void);
+static inline void disable_debug_registers(void)
+{
+	set_debugreg(0UL, 7);
+}
+
+/* For use by ptrace */
+unsigned long thread_get_debugreg(struct task_struct *tsk, int n);
+int thread_set_debugreg(struct task_struct *tsk, int n, unsigned long val);
+
+#endif	/* __KERNEL__ */
+
 #endif /* _ASM_X86_DEBUGREG_H */

Index: linux-HBKPT-2.6.28-rc7/arch/x86/include/asm/processor.h
===================================================================
@@ -401,13 +401,9 @@ struct thread_struct {
 	unsigned long		ip;
 	unsigned long		fs;
 	unsigned long		gs;
-	/* Hardware debugging registers: */
-	unsigned long		debugreg0;
-	unsigned long		debugreg1;
-	unsigned long		debugreg2;
-	unsigned long		debugreg3;
-	unsigned long		debugreg6;
-	unsigned long		debugreg7;
+/* Hardware breakpoint info */
+	unsigned long	vdr6;
+	struct thread_hw_breakpoint	*hw_breakpoint_info;
 	/* Fault info: */
 	unsigned long		cr2;
 	unsigned long		trap_no;

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/power/cpu_32.c
===================================================================
@@ -12,6 +12,7 @@
 #include <asm/mtrr.h>
 #include <asm/mce.h>
 #include <asm/xcr.h>
+#include <asm/debugreg.h>
 
 static struct saved_context saved_context;
 

@@ -47,6 +48,7 @@ static void __save_processor_state(struc
 	ctxt->cr2 = read_cr2();
 	ctxt->cr3 = read_cr3();
 	ctxt->cr4 = read_cr4_safe();
+	disable_debug_registers();
 }
 
 /* Needed by apm.c */

@@ -79,19 +81,7 @@ static void fix_processor_context(void)
 	load_TR_desc();				/* This does ltr */
 	load_LDT(&current->active_mm->context);	/* This does lldt */
 
-	/*
-	 * Now maybe reload the debug registers
-	 */
-	if (current->thread.debugreg7) {
-		set_debugreg(current->thread.debugreg0, 0);
-		set_debugreg(current->thread.debugreg1, 1);
-		set_debugreg(current->thread.debugreg2, 2);
-		set_debugreg(current->thread.debugreg3, 3);
-		/* no 4 and 5 */
-		set_debugreg(current->thread.debugreg6, 6);
-		set_debugreg(current->thread.debugreg7, 7);
-	}
-
+	load_debug_registers();
 }
 
 static void __restore_processor_state(struct saved_context *ctxt)

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/power/cpu_64.c
===================================================================
@@ -15,6 +15,7 @@
 #include <asm/pgtable.h>
 #include <asm/mtrr.h>
 #include <asm/xcr.h>
+#include <asm/debugreg.h>
 
 static void fix_processor_context(void);
 

@@ -70,6 +71,7 @@ static void __save_processor_state(struc
 	ctxt->cr3 = read_cr3();
 	ctxt->cr4 = read_cr4();
 	ctxt->cr8 = read_cr8();
+	disable_debug_registers();
 }
 
 void save_processor_state(void)

@@ -158,16 +160,5 @@ static void fix_processor_context(void)
 	load_TR_desc();				/* This does ltr */
 	load_LDT(&current->active_mm->context);	/* This does lldt */
 
-	/*
-	 * Now maybe reload the debug registers
-	 */
-	if (current->thread.debugreg7){
-                loaddebug(&current->thread, 0);
-                loaddebug(&current->thread, 1);
-                loaddebug(&current->thread, 2);
-                loaddebug(&current->thread, 3);
-                /* no 4 and 5 */
-                loaddebug(&current->thread, 6);
-                loaddebug(&current->thread, 7);
-	}
+	load_debug_registers();
 }

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/kernel/smpboot.c
===================================================================
@@ -62,6 +62,7 @@
 #include <asm/mtrr.h>
 #include <asm/vmi.h>
 #include <asm/genapic.h>
+#include <asm/debugreg.h>
 #include <linux/mc146818rtc.h>
 
 #include <mach_apic.h>

@@ -350,6 +351,7 @@ static void __cpuinit start_secondary(vo
 	setup_secondary_clock();
 
 	wmb();
+	load_debug_registers();
 	cpu_idle();
 }
 

@@ -1356,6 +1358,7 @@ void cpu_disable_common(void)
 	remove_cpu_from_maps(cpu);
 	unlock_vector_lock();
 	fixup_irqs(cpu_online_map);
+	disable_debug_registers();
 }
 
 int native_cpu_disable(void)

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/kernel/process_32.c
===================================================================
@@ -59,6 +59,8 @@
 #include <asm/idle.h>
 #include <asm/syscalls.h>
 #include <asm/smp.h>
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
 
 asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");
 

@@ -230,6 +232,8 @@ EXPORT_SYMBOL(kernel_thread);
  */
 void exit_thread(void)
 {
+	struct task_struct *tsk = current;
+
 	/* The process may have allocated an io port bitmap... nuke it. */
 	if (unlikely(test_thread_flag(TIF_IO_BITMAP))) {
 		struct task_struct *tsk = current;

@@ -250,6 +254,8 @@ void exit_thread(void)
 		tss->x86_tss.io_bitmap_base = INVALID_IO_BITMAP_OFFSET;
 		put_cpu();
 	}
+	if (unlikely(tsk->thread.hw_breakpoint_info))
+		flush_thread_hw_breakpoint(tsk);
 #ifdef CONFIG_X86_DS
 	/* Free any DS contexts that have not been properly released. */
 	if (unlikely(current->thread.ds_ctx)) {

@@ -264,14 +270,9 @@ void flush_thread(void)
 {
 	struct task_struct *tsk = current;
 
-	tsk->thread.debugreg0 = 0;
-	tsk->thread.debugreg1 = 0;
-	tsk->thread.debugreg2 = 0;
-	tsk->thread.debugreg3 = 0;
-	tsk->thread.debugreg6 = 0;
-	tsk->thread.debugreg7 = 0;
-	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));	
-	clear_tsk_thread_flag(tsk, TIF_DEBUG);
+	memset(tsk->thread.tls_array, 0, sizeof(tsk->thread.tls_array));
+	if (unlikely(tsk->thread.hw_breakpoint_info))
+		flush_thread_hw_breakpoint(tsk);
 	/*
 	 * Forget coprocessor state..
 	 */

@@ -315,7 +316,15 @@ int copy_thread(int nr, unsigned long cl
 
 	savesegment(gs, p->thread.gs);
 
+	p->thread.hw_breakpoint_info = NULL;
+	p->thread.io_bitmap_ptr = NULL;
+
 	tsk = current;
+	err = -ENOMEM;
+	if (unlikely(tsk->thread.hw_breakpoint_info)) {
+		if (copy_thread_hw_breakpoint(tsk, p, clone_flags))
+			goto out;
+	}
 	if (unlikely(test_tsk_thread_flag(tsk, TIF_IO_BITMAP))) {
 		p->thread.io_bitmap_ptr = kmemdup(tsk->thread.io_bitmap_ptr,
 						IO_BITMAP_BYTES, GFP_KERNEL);

@@ -335,10 +344,14 @@ int copy_thread(int nr, unsigned long cl
 		err = do_set_thread_area(p, -1,
 			(struct user_desc __user *)childregs->si, 0);
 
+out:
 	if (err && p->thread.io_bitmap_ptr) {
 		kfree(p->thread.io_bitmap_ptr);
 		p->thread.io_bitmap_max = 0;
 	}
+	if (err)
+		flush_thread_hw_breakpoint(p);
+
 	return err;
 }
 

@@ -463,16 +476,6 @@ __switch_to_xtra(struct task_struct *pre
 	if (next->debugctlmsr != debugctl)
 		update_debugctlmsr(next->debugctlmsr);
 
-	if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
-		set_debugreg(next->debugreg0, 0);
-		set_debugreg(next->debugreg1, 1);
-		set_debugreg(next->debugreg2, 2);
-		set_debugreg(next->debugreg3, 3);
-		/* no 4 and 5 */
-		set_debugreg(next->debugreg6, 6);
-		set_debugreg(next->debugreg7, 7);
-	}
-
 	if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
 	    test_tsk_thread_flag(next_p, TIF_NOTSC)) {
 		/* prev and next are different */

@@ -628,6 +631,12 @@ struct task_struct * __switch_to(struct 
 		loadsegment(gs, next->gs);
 
 	x86_write_percpu(current_task, next_p);
+	/*
+	 * Handle debug registers.  This must be done _after_ current
+	 * is updated.
+	 */
+	if (unlikely(test_tsk_thread_flag(next_p, TIF_DEBUG)))
+		switch_to_thread_hw_breakpoint(next_p);
 
 	return prev_p;
 }

90 lines not on this page · raw message

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/kernel/signal_32.c
===================================================================
@@ -622,15 +622,6 @@ static void do_signal(struct pt_regs *re
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 	if (signr > 0) {
-		/*
-		 * Re-enable any watchpoints before delivering the
-		 * signal to user space. The processor register will
-		 * have been cleared if the watchpoint triggered
-		 * inside the kernel.
-		 */
-		if (current->thread.debugreg7)
-			set_debugreg(current->thread.debugreg7, 7);
-
 		/* Whee! Actually deliver the signal.  */
 		if (handle_signal(signr, &info, &ka, oldset, regs) == 0) {
 			/*

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/kernel/signal_64.c
===================================================================
@@ -422,15 +422,6 @@ static void do_signal(struct pt_regs *re
 
 	signr = get_signal_to_deliver(&info, &ka, regs, NULL);
 	if (signr > 0) {
-		/*
-		 * Re-enable any watchpoints before delivering the
-		 * signal to user space. The processor register will
-		 * have been cleared if the watchpoint triggered
-		 * inside the kernel.
-		 */
-		if (current->thread.debugreg7)
-			set_debugreg(current->thread.debugreg7, 7);
-
 		/* Whee! Actually deliver the signal.  */
 		if (handle_signal(signr, &info, &ka, oldset, regs) == 0) {
 			/*

Index: linux-HBKPT-2.6.28-rc7/arch/x86/kernel/ptrace.c
===================================================================
@@ -33,6 +33,7 @@
 #include <asm/prctl.h>
 #include <asm/proto.h>
 #include <asm/ds.h>
+#include <asm/hw_breakpoint.h>
 
 #include "tls.h"
 

@@ -466,95 +467,168 @@ static int genregs_set(struct task_struc
 }
 
 /*
- * This function is trivial and will be inlined by the compiler.
- * Having it separates the implementation details of debug
- * registers from the interface details of ptrace.
+ * Decode the length and type bits for a particular breakpoint as
+ * stored in debug register 7.  Return the "enabled" status.
  */
-static unsigned long ptrace_get_debugreg(struct task_struct *child, int n)
+static int decode_dr7(unsigned long dr7, int bpnum, unsigned *len,
+		unsigned *type)
 {
-	switch (n) {
-	case 0:		return child->thread.debugreg0;
-	case 1:		return child->thread.debugreg1;
-	case 2:		return child->thread.debugreg2;
-	case 3:		return child->thread.debugreg3;
-	case 6:		return child->thread.debugreg6;
-	case 7:		return child->thread.debugreg7;
+	int temp = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
+
+	*len = (temp & 0xc) | 0x40;
+	*type = (temp & 0x3) | 0x80;
+	return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
+}
+
+static void ptrace_triggered(struct hw_breakpoint *bp, struct pt_regs *regs)
+{
+	struct task_struct *tsk = current;
+	struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+	int i;
+
+	/* Store in the virtual DR6 register the fact that the breakpoint
+	 * was hit so the thread's debugger will see it.
+	 */
+	if (thbi) {
+		i = bp - thbi->vdr_bps;
+		tsk->thread.vdr6 |= (DR_TRAP0 << i);
 	}
-	return 0;
 }
 
-static int ptrace_set_debugreg(struct task_struct *child,
-			       int n, unsigned long data)
+/*
+ * Handle ptrace writes to debug register 7.
+ */
+static int ptrace_write_dr7(struct task_struct *tsk,
+		struct thread_hw_breakpoint *thbi, unsigned long data)
 {
+	struct hw_breakpoint *bp;
 	int i;
+	int rc = 0;
+	unsigned long old_dr7 = thbi->vdr7;
 
-	if (unlikely(n == 4 || n == 5))
-		return -EIO;
+	data &= ~DR_CONTROL_RESERVED;
 
-	if (n < 4 && unlikely(data >= debugreg_addr_limit(child)))
-		return -EIO;
+	/* Loop through all the hardware breakpoints, making the
+	 * appropriate changes to each.
+	 */
+ restore_settings:
+	thbi->vdr7 = data;
+	bp = &thbi->vdr_bps[0];
+	for (i = 0; i < HB_NUM; (++i, ++bp)) {
+		int enabled;
+		unsigned len, type;
+
+		enabled = decode_dr7(data, i, &len, &type);
+
+		/* Unregister the breakpoint before trying to change it */
+		if (bp->status)
+			__unregister_user_hw_breakpoint(tsk, bp);
 
-	switch (n) {
-	case 0:		child->thread.debugreg0 = data; break;
-	case 1:		child->thread.debugreg1 = data; break;
-	case 2:		child->thread.debugreg2 = data; break;
-	case 3:		child->thread.debugreg3 = data; break;
+		/* Now register the breakpoint if it should be enabled.
+		 * New invalid entries will raise an error here.
+		 */
+		if (enabled) {
+			bp->triggered = ptrace_triggered;
 
-	case 6:
-		if ((data & ~0xffffffffUL) != 0)
-			return -EIO;
-		child->thread.debugreg6 = data;
-		break;
+			bp->priority = HW_BREAKPOINT_PRIO_PTRACE;
+			if (rc == 0 && __register_user_hw_breakpoint(tsk, bp,
+					bp->info.address, len, type) < 0)
+				break;
+		}
+	}
 
-	case 7:
-		/*
-		 * Sanity-check data. Take one half-byte at once with
-		 * check = (val >> (16 + 4*i)) & 0xf. It contains the
-		 * R/Wi and LENi bits; bits 0 and 1 are R/Wi, and bits
-		 * 2 and 3 are LENi. Given a list of invalid values,
-		 * we do mask |= 1 << invalid_value, so that
-		 * (mask >> check) & 1 is a correct test for invalid
-		 * values.
-		 *
-		 * R/Wi contains the type of the breakpoint /
-		 * watchpoint, LENi contains the length of the watched
-		 * data in the watchpoint case.
-		 *
-		 * The invalid values are:
-		 * - LENi == 0x10 (undefined), so mask |= 0x0f00.	[32-bit]
-		 * - R/Wi == 0x10 (break on I/O reads or writes), so
-		 *   mask |= 0x4444.
-		 * - R/Wi == 0x00 && LENi != 0x00, so we have mask |=
-		 *   0x1110.
-		 *
-		 * Finally, mask = 0x0f00 | 0x4444 | 0x1110 == 0x5f54.
-		 *
-		 * See the Intel Manual "System Programming Guide",
-		 * 15.2.4
-		 *
-		 * Note that LENi == 0x10 is defined on x86_64 in long
-		 * mode (i.e. even for 32-bit userspace software, but
-		 * 64-bit kernel), so the x86_64 mask value is 0x5454.
-		 * See the AMD manual no. 24593 (AMD64 System Programming)
+	/* If anything above failed, restore the original settings */
+	if (i < HB_NUM) {
+		rc = -EIO;
+		data = old_dr7;
+		goto restore_settings;
+	}
+	return rc;
+}
+
+/*
+ * Handle PTRACE_PEEKUSR calls for the debug register area.
+ */
+unsigned long ptrace_get_debugreg(struct task_struct *tsk, int n)
+{
+	struct thread_hw_breakpoint *thbi;
+	unsigned long val = 0;
+
+	mutex_lock(&hw_breakpoint_mutex);
+	thbi = tsk->thread.hw_breakpoint_info;
+	if (n < HB_NUM) {
+		if (thbi)
+			val = thbi->vdr_bps[n].info.address;
+	} else if (n == 6) {
+		val = tsk->thread.vdr6;
+	} else if (n == 7) {
+		if (thbi)
+			val = thbi->vdr7;
+	}
+	mutex_unlock(&hw_breakpoint_mutex);
+	return val;
+}
+
+/*
+ * Handle PTRACE_POKEUSR calls for the debug register area.
+ */
+int ptrace_set_debugreg(struct task_struct *tsk, int n, unsigned long val)
+{
+	struct thread_hw_breakpoint *thbi;
+	int rc = -EIO;
+
+	/* We have to hold this lock the entire time, to prevent thbi
+	 * from being deallocated out from under us.
+	 */
+	mutex_lock(&hw_breakpoint_mutex);
+
+	/* There are no DR4 or DR5 registers */
+	if (n == 4 || n == 5)
+		;
+
+	/* Writes to DR6 modify the virtualized value */
+	else if (n == 6) {
+		tsk->thread.vdr6 = val;
+		rc = 0;
+	}
+
+	else if (!tsk->thread.hw_breakpoint_info && val == 0)
+		rc = 0;		/* Minor optimization */
+
+	else if ((thbi = alloc_thread_hw_breakpoint(tsk)) == NULL)
+		rc = -ENOMEM;
+
+	/* Writes to DR0 - DR3 change a breakpoint address */
+	else if (n < HB_NUM) {
+		struct hw_breakpoint *bp = &thbi->vdr_bps[n];
+
+		/* If the breakpoint is registered then unregister it,
+		 * change it, and re-register it.  Revert to the original
+		 * address if an error occurs.
 		 */
-#ifdef CONFIG_X86_32
-#define	DR7_MASK	0x5f54
-#else
-#define	DR7_MASK	0x5554
-#endif
-		data &= ~DR_CONTROL_RESERVED;
-		for (i = 0; i < 4; i++)
-			if ((DR7_MASK >> ((data >> (16 + 4*i)) & 0xf)) & 1)
-				return -EIO;
-		child->thread.debugreg7 = data;
-		if (data)
-			set_tsk_thread_flag(child, TIF_DEBUG);
-		else
-			clear_tsk_thread_flag(child, TIF_DEBUG);
-		break;
+		if (bp->status) {
+			unsigned long old_addr = bp->info.address;
+
+			__unregister_user_hw_breakpoint(tsk, bp);
+			rc = __register_user_hw_breakpoint(tsk, bp,
+					val, bp->info.len, bp->info.type);
+			if (rc < 0) {
+				__register_user_hw_breakpoint(tsk, bp,
+						old_addr,
+						bp->info.len, bp->info.type);
+			}
+		} else {
+			bp->info.address = val;
+			rc = 0;
+		}
 	}
 
-	return 0;
+	/* All that's left is DR7 */
+	else
+		rc = ptrace_write_dr7(tsk, thbi, val);
+
+	mutex_unlock(&hw_breakpoint_mutex);
+	return rc;
 }
 
 /*

@@ -1008,7 +1082,7 @@ long arch_ptrace(struct task_struct *chi
 		else if (addr >= offsetof(struct user, u_debugreg[0]) &&
 			 addr <= offsetof(struct user, u_debugreg[7])) {
 			addr -= offsetof(struct user, u_debugreg[0]);
-			tmp = ptrace_get_debugreg(child, addr / sizeof(data));
+			tmp = ptrace_get_debugreg(child, addr/sizeof(data));
 		}
 		ret = put_user(tmp, datap);
 		break;

@@ -1026,7 +1100,7 @@ long arch_ptrace(struct task_struct *chi
 			 addr <= offsetof(struct user, u_debugreg[7])) {
 			addr -= offsetof(struct user, u_debugreg[0]);
 			ret = ptrace_set_debugreg(child,
-						  addr / sizeof(data), data);
+						addr/sizeof(data), data);
 		}
 		break;
 

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/kernel/machine_kexec_32.c
===================================================================
@@ -24,6 +24,7 @@
 #include <asm/desc.h>
 #include <asm/system.h>
 #include <asm/cacheflush.h>
+#include <asm/debugreg.h>
 
 #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
 static u32 kexec_pgd[1024] PAGE_ALIGNED;

@@ -131,6 +132,7 @@ void machine_kexec(struct kimage *image)
 
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
+	disable_debug_registers();
 
 	if (image->preserve_context) {
 #ifdef CONFIG_X86_IO_APIC

Index: linux-2.6.28-rc5-bkpt-latest/arch/x86/kernel/machine_kexec_64.c
===================================================================
@@ -17,6 +17,7 @@
 #include <asm/tlbflush.h>
 #include <asm/mmu_context.h>
 #include <asm/io.h>
+#include <asm/debugreg.h>
 
 #define PAGE_ALIGNED __attribute__ ((__aligned__(PAGE_SIZE)))
 static u64 kexec_pgd[512] PAGE_ALIGNED;

@@ -190,6 +191,7 @@ void machine_kexec(struct kimage *image)
 
 	/* Interrupts aren't acceptable while we reboot */
 	local_irq_disable();
+	disable_debug_registers();
 
 	control_page = page_address(image->control_code_page) + PAGE_SIZE;
 	memcpy(control_page, relocate_kernel, PAGE_SIZE);