2009-01-29 07:49:14

by K.Prasad

Subject: [Patch 0/10] Hardware Breakpoint interfaces

Hi Andrew and all,
Please find the patches that introduce interfaces to access
Hardware Breakpoint (or watchpoint) registers and an arch-specific
implementation for x86/x86_64 architecture. Can you consider them for
inclusion in -mm tree?

A short description of the framework and interfaces is provided
below. Some of the details will be specific to x86/x86_64 architecture
and may vary depending upon the support provided by the target
processor.

Description
------------

The Hardware Breakpoint registers can be used for tracing changes to a
variable or data location (even I/O ports in x86/x86_64) and will be
extremely helpful in debugging problems such as memory corruption. While
these registers have been used by user-space debuggers for long (through
'ptrace' syscalls), KGDB exploited them for kernel-space addresses.

The proposed framework, introduces interfaces to use them directly on
both user- and kernel-space addresses apart from arbitrating requests
from various such users for the limited number of registers.

The interfaces are:

int register_kernel_hw_breakpoint(struct hw_breakpoint *);
void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp);

int register_user_hw_breakpoint(struct task_struct *tsk,
struct hw_breakpoint *bp);
void unregister_user_hw_breakpoint(struct task_struct *tsk,
struct hw_breakpoint *bp);

The 'struct hw_breakpoint' will be the anchor data-structure containing
all the necessary information such as name or address, type, length,
priority and pointers to handler functions (some of which are
arch-specific). More information about the role of each field, the handler
functions and their return values can be found in the descriptive comments
preceding these functions and in "include/asm-generic/hw_breakpoint.h".

While (un)register_user_hw_breakpoint() isn't exported yet, its
worker-routine __register_user-hw_breakpoint() is used by ptrace syscall
for all breakpoint register requirements. For the kernel-space, a simple
use case to trace 'write' operations on a kernel variable can be found
in samples/hw_breakpoint/data_breakpoint.c.

In the current patchset, support is provided only for read and
read-write breakpoints on data locations, which can be later expand to
include instruction and I/O breakpoints for x86/x86_64.

The patches are based on 2.6.29-rc2 and have been tested on an x86
machine along with concurrent sessions of a kprobe-module and a GDB
session using HW breakpoints on the target program.

There is pending integration with 'KGDB' without which mutual exclusion
between them (KGDB and HW breakpoint use through above interfaces) needs
to be observed.

Several enhancements including support for more architectures and types
of breakpoints are contemplated in the revisions to come.

Let me know your thoughts on this.

Thanks,
K.Prasad

2009-01-29 07:54:19

by K.Prasad

Subject: [Patch 1/10] Introducing generic hardware breakpoint handler interfaces

This patch introduces two new files hw_breakpoint.[ch] which defines the
generic interfaces to use hardware breakpoint infrastructure of the system.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
include/asm-generic/hw_breakpoint.h | 229 +++++++++++
kernel/hw_breakpoint.c | 722 ++++++++++++++++++++++++++++++++++++
2 files changed, 951 insertions(+)

Index: linux-hbkpt-lkml-29-rc2/include/asm-generic/hw_breakpoint.h
===================================================================
--- /dev/null
+++ linux-hbkpt-lkml-29-rc2/include/asm-generic/hw_breakpoint.h
@@ -0,0 +1,229 @@
+#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>
+#include <linux/kallsyms.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 @triggered 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. 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 @triggered routine
+ * 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>
+ *
+ * struct hw_breakpoint my_bp;
+ *
+ * static void my_triggered(struct hw_breakpoint *bp, struct pt_regs *regs)
+ * {
+ * printk(KERN_DEBUG "Inside triggered routine of breakpoint exception\n");
+ * dump_stack();
+ * .......<more debugging output>........
+ * }
+ *
+ * static struct hw_breakpoint my_bp;
+ *
+ * static int init_module(void)
+ * {
+ * ..........<do anything>............
+ * my_bp.info.type = HW_BREAKPOINT_WRITE;
+ * my_bp.info.len = HW_BREAKPOINT_LEN_4;
+ * my_bp.info.priority = HW_BREAKPOINT_PRIO_NORMAL;
+ *
+ * my_bp.installed = (void *)my_bp_installed;
+ * my_bp.uninstalled = (void *)my_bp_uninstalled;
+ * my_bp.triggered = (void *)my_triggered;
+ *
+ * rc = register_kernel_hw_breakpoint(&my_bp);
+ * ..........<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);
+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);
+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 */
Index: linux-hbkpt-lkml-29-rc2/kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ linux-hbkpt-lkml-29-rc2/kernel/hw_breakpoint.c
@@ -0,0 +1,722 @@
+/*
+ * 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
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ *
+ * This file contains the arch-independent routines. It is not meant
+ * to be compiled as a standalone source file; rather it should be
+ * #include'd by the arch-specific implementation.
+ */
+
+
+/*
+ * Install the debug register values for a new thread.
+ */
+void switch_to_thread_hw_breakpoint(struct task_struct *tsk)
+{
+ struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+ struct cpu_hw_breakpoint *chbi;
+ struct kernel_bp_data *thr_kbpdata;
+
+ /* This routine is on the hot path; it gets called for every
+ * context switch into a task with active breakpoints. We
+ * must make sure that the common case executes as quickly as
+ * possible.
+ */
+ chbi = &per_cpu(cpu_info, get_cpu());
+ chbi->bp_task = tsk;
+
+ /* Use RCU to synchronize with external updates */
+ rcu_read_lock();
+
+ /* Other CPUs might be making updates to the list of kernel
+ * breakpoints at this time. If they are, they will modify
+ * the other entry in kbpdata[] -- the one not pointed to
+ * by chbi->cur_kbpdata. So the update itself won't affect
+ * us directly.
+ *
+ * However when the update is finished, an IPI will arrive
+ * telling this CPU to change chbi->cur_kbpdata. We need
+ * to use a single consistent kbpdata[] entry, the present one.
+ * So we'll copy the pointer to a local variable, thr_kbpdata,
+ * and we must prevent the compiler from aliasing the two
+ * pointers. Only a compiler barrier is required, not a full
+ * memory barrier, because everything takes place on a single CPU.
+ */
+ restart:
+ thr_kbpdata = chbi->cur_kbpdata;
+ barrier();
+
+ /* Normally we can keep the same debug register settings as the
+ * last time this task ran. But if the kernel breakpoints have
+ * changed or any user breakpoints have been registered or
+ * unregistered, we need to handle the updates and possibly
+ * send out some notifications.
+ */
+ if (unlikely(thbi->gennum != thr_kbpdata->gennum)) {
+ struct hw_breakpoint *bp;
+ int i;
+ int num;
+
+ thbi->gennum = thr_kbpdata->gennum;
+ arch_update_thbi(thbi, thr_kbpdata);
+ num = thr_kbpdata->num_kbps;
+
+ /* This code can be invoked while a debugger is actively
+ * updating the thread's breakpoint list. We use RCU to
+ * protect our access to the list pointers. */
+ thbi->num_installed = 0;
+ i = HB_NUM;
+ list_for_each_entry_rcu(bp, &thbi->thread_bps, node) {
+
+ /* If this register is allocated for kernel bps,
+ * don't install. Otherwise do. */
+ if (--i < num) {
+ if (bp->status == HW_BREAKPOINT_INSTALLED) {
+ if (bp->uninstalled)
+ (bp->uninstalled)(bp);
+ bp->status = HW_BREAKPOINT_REGISTERED;
+ }
+ } else {
+ ++thbi->num_installed;
+ if (bp->status != HW_BREAKPOINT_INSTALLED) {
+ bp->status = HW_BREAKPOINT_INSTALLED;
+ if (bp->installed)
+ (bp->installed)(bp);
+ }
+ }
+ }
+ }
+
+ /* Set the debug register */
+ arch_install_thbi(thbi);
+
+ /* Were there any kernel breakpoint changes while we were running? */
+ if (unlikely(chbi->cur_kbpdata != thr_kbpdata)) {
+
+ /* Some debug registers now be assigned to kernel bps and
+ * we might have messed them up. Reload all the kernel bps
+ * and then reload the thread bps.
+ */
+ arch_install_chbi(chbi);
+ goto restart;
+ }
+
+ rcu_read_unlock();
+ put_cpu_no_resched();
+}
+
+/*
+ * Install the debug register values for just the kernel, no thread.
+ */
+static void switch_to_none_hw_breakpoint(void)
+{
+ struct cpu_hw_breakpoint *chbi;
+
+ chbi = &per_cpu(cpu_info, get_cpu());
+ chbi->bp_task = NULL;
+
+ /* This routine gets called from only two places. In one
+ * the caller holds the hw_breakpoint_mutex; in the other
+ * interrupts are disabled. In either case, no kernel
+ * breakpoint updates can arrive while the routine runs.
+ * So we don't need to use RCU.
+ */
+ arch_install_none(chbi);
+ put_cpu_no_resched();
+}
+
+/*
+ * Update the debug registers on this CPU.
+ */
+static void update_this_cpu(void *unused)
+{
+ struct cpu_hw_breakpoint *chbi;
+ struct task_struct *tsk = current;
+
+ chbi = &per_cpu(cpu_info, get_cpu());
+
+ /* Install both the kernel and the user breakpoints */
+ arch_install_chbi(chbi);
+ if (test_tsk_thread_flag(tsk, TIF_DEBUG))
+ switch_to_thread_hw_breakpoint(tsk);
+
+ put_cpu_no_resched();
+}
+
+/*
+ * Tell all CPUs to update their debug registers.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static void update_all_cpus(void)
+{
+ /* We don't need to use any sort of memory barrier. The IPI
+ * carried out by on_each_cpu() includes its own barriers.
+ */
+ on_each_cpu(update_this_cpu, NULL, 0);
+ synchronize_rcu();
+}
+
+/*
+ * Load the debug registers during startup of a CPU.
+ */
+void load_debug_registers(void)
+{
+ unsigned long flags;
+
+ /* Prevent IPIs for new kernel breakpoint updates */
+ local_irq_save(flags);
+
+ rcu_read_lock();
+ update_this_cpu(NULL);
+ rcu_read_unlock();
+
+ local_irq_restore(flags);
+}
+
+/*
+ * Take the 4 highest-priority breakpoints in a thread and accumulate
+ * their priorities in tprio. Highest-priority entry is in tprio[3].
+ */
+static void accum_thread_tprio(struct thread_hw_breakpoint *thbi)
+{
+ int i;
+
+ for (i = HB_NUM - 1; i >= 0 && thbi->bps[i]; --i)
+ tprio[i] = max(tprio[i], thbi->bps[i]->priority);
+}
+
+/*
+ * Recalculate the value of the tprio array, the maximum priority levels
+ * requested by user breakpoints in all threads.
+ *
+ * Each thread has a list of registered breakpoints, kept in order of
+ * decreasing priority. We'll set tprio[0] to the maximum priority of
+ * the first entries in all the lists, tprio[1] to the maximum priority
+ * of the second entries in all the lists, etc. In the end, we'll know
+ * that no thread requires breakpoints with priorities higher than the
+ * values in tprio.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static void recalc_tprio(void)
+{
+ struct thread_hw_breakpoint *thbi;
+
+ memset(tprio, 0, sizeof tprio);
+
+ /* Loop through all threads having registered breakpoints
+ * and accumulate the maximum priority levels in tprio.
+ */
+ list_for_each_entry(thbi, &thread_list, node)
+ accum_thread_tprio(thbi);
+}
+
+/*
+ * Decide how many debug registers will be allocated to kernel breakpoints
+ * and consequently, how many remain available for user breakpoints.
+ *
+ * The priorities of the entries in the list of registered kernel bps
+ * are compared against the priorities stored in tprio[]. The 4 highest
+ * winners overall get to be installed in a debug register; num_kpbs
+ * keeps track of how many of those winners come from the kernel list.
+ *
+ * If num_kbps changes, or if a kernel bp changes its installation status,
+ * then call update_all_cpus() so that the debug registers will be set
+ * correctly on every CPU. If neither condition holds then the set of
+ * kernel bps hasn't changed, and nothing more needs to be done.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+static void balance_kernel_vs_user(void)
+{
+ int k, u;
+ int changed = 0;
+ struct hw_breakpoint *bp;
+ struct kernel_bp_data *new_kbpdata;
+
+ /* Determine how many debug registers are available for kernel
+ * breakpoints as opposed to user breakpoints, based on the
+ * priorities. Ties are resolved in favor of user bps.
+ */
+ k = 0; /* Next kernel bp to allocate */
+ u = HB_NUM - 1; /* Next user bp to allocate */
+
+ bp = list_entry(kernel_bps.next, struct hw_breakpoint, node);
+ while (k <= u) {
+ if (&bp->node == &kernel_bps || tprio[u] >= bp->priority)
+ --u; /* User bps win a slot */
+ else {
+ ++k; /* Kernel bp wins a slot */
+ if (bp->status != HW_BREAKPOINT_INSTALLED)
+ changed = 1;
+ bp = list_entry(bp->node.next, struct hw_breakpoint,
+ node);
+ }
+ }
+ if (k != cur_kbpdata->num_kbps)
+ changed = 1;
+
+ /* Notify the remaining kernel breakpoints that they are about
+ * to be uninstalled.
+ */
+ list_for_each_entry_from(bp, &kernel_bps, node) {
+ if (bp->status == HW_BREAKPOINT_INSTALLED) {
+ if (bp->uninstalled)
+ (bp->uninstalled)(bp);
+ bp->status = HW_BREAKPOINT_REGISTERED;
+ changed = 1;
+ }
+ }
+
+ if (changed) {
+ cur_kbpindex ^= 1;
+ new_kbpdata = &kbpdata[cur_kbpindex];
+ new_kbpdata->gennum = cur_kbpdata->gennum + 1;
+ new_kbpdata->num_kbps = k;
+ arch_new_kbpdata(new_kbpdata);
+ u = 0;
+ list_for_each_entry(bp, &kernel_bps, node) {
+ if (u >= k)
+ break;
+ new_kbpdata->bps[u] = bp;
+ ++u;
+ }
+ rcu_assign_pointer(cur_kbpdata, new_kbpdata);
+
+ /* Tell all the CPUs to update their debug registers */
+ update_all_cpus();
+
+ /* Notify the breakpoints that just got installed */
+ for (u = 0; u < k; ++u) {
+ bp = new_kbpdata->bps[u];
+ if (bp->status != HW_BREAKPOINT_INSTALLED) {
+ bp->status = HW_BREAKPOINT_INSTALLED;
+ if (bp->installed)
+ (bp->installed)(bp);
+ }
+ }
+ }
+}
+
+/*
+ * Return the pointer to a thread's hw_breakpoint info area,
+ * and try to allocate one if it doesn't exist.
+ *
+ * The caller must hold hw_breakpoint_mutex.
+ */
+struct thread_hw_breakpoint *alloc_thread_hw_breakpoint(
+ struct task_struct *tsk)
+{
+ if (!tsk->thread.hw_breakpoint_info && !(tsk->flags & PF_EXITING)) {
+ struct thread_hw_breakpoint *thbi;
+
+ thbi = kzalloc(sizeof(struct thread_hw_breakpoint),
+ GFP_KERNEL);
+ if (thbi) {
+ INIT_LIST_HEAD(&thbi->node);
+ INIT_LIST_HEAD(&thbi->thread_bps);
+
+ /* Force an update the next time tsk runs */
+ thbi->gennum = cur_kbpdata->gennum - 2;
+ tsk->thread.hw_breakpoint_info = thbi;
+ }
+ }
+ return tsk->thread.hw_breakpoint_info;
+}
+
+/*
+ * 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)
+{
+ struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+ struct hw_breakpoint *bp;
+
+ if (!thbi)
+ return;
+ mutex_lock(&hw_breakpoint_mutex);
+
+ /* Let the breakpoints know they are being uninstalled */
+ list_for_each_entry(bp, &thbi->thread_bps, node) {
+ if (bp->status == HW_BREAKPOINT_INSTALLED && bp->uninstalled)
+ (bp->uninstalled)(bp);
+ bp->status = 0;
+ }
+
+ /* Remove tsk from the list of all threads with registered bps */
+ list_del(&thbi->node);
+
+ /* The thread no longer has any breakpoints associated with it */
+ clear_tsk_thread_flag(tsk, TIF_DEBUG);
+ tsk->thread.hw_breakpoint_info = NULL;
+ kfree(thbi);
+
+ /* Recalculate and rebalance the kernel-vs-user priorities */
+ recalc_tprio();
+ balance_kernel_vs_user();
+
+ /* Actually uninstall the breakpoints if necessary */
+ if (tsk == current)
+ switch_to_none_hw_breakpoint();
+ mutex_unlock(&hw_breakpoint_mutex);
+}
+
+/*
+ * 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);
+ return 0;
+}
+
+/*
+ * Store the highest-priority thread breakpoint entries in an array.
+ */
+static void store_thread_bp_array(struct thread_hw_breakpoint *thbi)
+{
+ struct hw_breakpoint *bp;
+ int i;
+
+ i = HB_NUM - 1;
+ list_for_each_entry(bp, &thbi->thread_bps, node) {
+ thbi->bps[i] = bp;
+ arch_store_thread_bp_array(thbi, bp, i);
+ if (--i < 0)
+ break;
+ }
+ while (i >= 0)
+ thbi->bps[i--] = NULL;
+
+ /* Force an update the next time this task runs */
+ thbi->gennum = cur_kbpdata->gennum - 2;
+}
+
+/*
+ * Insert a new breakpoint in a priority-sorted list.
+ * Return the bp's index in the list.
+ *
+ * Thread invariants:
+ * tsk_thread_flag(tsk, TIF_DEBUG) set implies
+ * tsk->thread.hw_breakpoint_info is not NULL.
+ * tsk_thread_flag(tsk, TIF_DEBUG) set iff thbi->thread_bps is non-empty
+ * iff thbi->node is on thread_list.
+ */
+static int insert_bp_in_list(struct hw_breakpoint *bp,
+ struct thread_hw_breakpoint *thbi, struct task_struct *tsk)
+{
+ struct list_head *head;
+ int pos;
+ struct hw_breakpoint *temp_bp;
+
+ /* tsk and thbi are NULL for kernel bps, non-NULL for user bps */
+ if (tsk)
+ head = &thbi->thread_bps;
+ else
+ head = &kernel_bps;
+
+ /* Equal-priority breakpoints get listed first-come-first-served */
+ pos = 0;
+ list_for_each_entry(temp_bp, head, node) {
+ if (bp->priority > temp_bp->priority)
+ break;
+ ++pos;
+ }
+ bp->status = HW_BREAKPOINT_REGISTERED;
+ list_add_tail(&bp->node, &temp_bp->node);
+
+ if (tsk) {
+ store_thread_bp_array(thbi);
+
+ /* Is this the thread's first registered breakpoint? */
+ if (list_empty(&thbi->node)) {
+ set_tsk_thread_flag(tsk, TIF_DEBUG);
+ list_add(&thbi->node, &thread_list);
+ }
+ }
+ return pos;
+}
+
+/*
+ * Remove a breakpoint from its priority-sorted list.
+ *
+ * See the invariants mentioned above.
+ */
+static void remove_bp_from_list(struct hw_breakpoint *bp,
+ struct thread_hw_breakpoint *thbi, struct task_struct *tsk)
+{
+ /* Remove bp from the thread's/kernel's list. If the list is now
+ * empty we must clear the TIF_DEBUG flag. But keep the
+ * thread_hw_breakpoint structure, so that the virtualized debug
+ * register values will remain valid.
+ */
+ list_del(&bp->node);
+ if (tsk) {
+ store_thread_bp_array(thbi);
+
+ if (list_empty(&thbi->thread_bps)) {
+ list_del_init(&thbi->node);
+ clear_tsk_thread_flag(tsk, TIF_DEBUG);
+ }
+ }
+
+ /* Tell the breakpoint it is being uninstalled */
+ if (bp->status == HW_BREAKPOINT_INSTALLED && bp->uninstalled)
+ (bp->uninstalled)(bp);
+ bp->status = 0;
+}
+
+/*
+ * Validate the settings in a hw_breakpoint structure.
+ */
+static int validate_settings(struct hw_breakpoint *bp, struct task_struct *tsk)
+{
+ int ret;
+ unsigned int align;
+
+ ret = arch_validate_hwbkpt_settings(bp, &align, tsk);
+ if (ret < 0)
+ goto err;
+
+ /* Check that the low-order bits of the address are appropriate
+ * for the alignment implied by len.
+ */
+ if (bp->info.address & align)
+ return -EINVAL;
+
+ /* Check that the virtual address is in the proper range */
+ if (tsk) {
+ if (!arch_check_va_in_userspace(bp->info.address, tsk))
+ return -EFAULT;
+ } else {
+ if (!arch_check_va_in_kernelspace(bp->info.address))
+ return -EFAULT;
+ }
+ err:
+ return ret;
+}
+
+/*
+ * Actual implementation of register_user_hw_breakpoint.
+ */
+int __register_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ int rc;
+ struct thread_hw_breakpoint *thbi;
+ int pos;
+
+ bp->status = 0;
+ rc = validate_settings(bp, tsk);
+ if (rc)
+ return rc;
+
+ thbi = alloc_thread_hw_breakpoint(tsk);
+ if (!thbi)
+ return -ENOMEM;
+
+ /* Insert bp in the thread's list */
+ pos = insert_bp_in_list(bp, thbi, tsk);
+ arch_register_user_hw_breakpoint(bp, thbi);
+
+ /* Update and rebalance the priorities. We don't need to go through
+ * the list of all threads; adding a breakpoint can only cause the
+ * priorities for this thread to increase.
+ */
+ accum_thread_tprio(thbi);
+ balance_kernel_vs_user();
+
+ /* Did bp get allocated to a debug register? We can tell from its
+ * position in the list. The number of registers allocated to
+ * kernel breakpoints is num_kbps; all the others are available for
+ * user breakpoints. If bp's position in the priority-ordered list
+ * is low enough, it will get a register.
+ */
+ if (pos < HB_NUM - cur_kbpdata->num_kbps) {
+ rc = 1;
+
+ /* Does it need to be installed right now? */
+ if (tsk == current)
+ switch_to_thread_hw_breakpoint(tsk);
+ /* Otherwise it will get installed the next time tsk runs */
+ }
+
+ return rc;
+}
+
+/**
+ * register_user_hw_breakpoint - register a hardware breakpoint for user space
+ * @tsk: the task in whose memory space the breakpoint will be set
+ * @bp: the breakpoint structure to register
+ * @address: location (virtual address) of the breakpoint
+ * @len: encoded extent of the breakpoint address (1, 2, 4, or 8 bytes)
+ * @type: breakpoint type (read-only, write-only, read-write, or execute)
+ *
+ * This routine registers a breakpoint to be associated with @tsk's
+ * memory space and active only while @tsk is running. It does not
+ * guarantee that the breakpoint will be allocated to a debug register
+ * immediately; there may be other higher-priority breakpoints registered
+ * which require the use of all the debug registers.
+ *
+ * @tsk will normally be a process being debugged by the current process,
+ * but it may also be the current process.
+ *
+ * @bp->address, @bp->len, @bp->type, @bp->triggered and @bp->priority must be
+ * set properly before invocation
+ *
+ * Returns 1 if @bp is allocated to a debug register, 0 if @bp is
+ * registered but not allowed to be installed, otherwise a negative error
+ * code.
+ */
+int register_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ int rc;
+
+ mutex_lock(&hw_breakpoint_mutex);
+ rc = __register_user_hw_breakpoint(tsk, bp);
+ mutex_unlock(&hw_breakpoint_mutex);
+ return rc;
+}
+
+/*
+ * Actual implementation of unregister_user_hw_breakpoint.
+ */
+void __unregister_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ struct thread_hw_breakpoint *thbi = tsk->thread.hw_breakpoint_info;
+
+ if (!bp->status)
+ return; /* Not registered */
+
+ /* Remove bp from the thread's list */
+ remove_bp_from_list(bp, thbi, tsk);
+ arch_unregister_user_hw_breakpoint(bp, thbi);
+
+ /* Recalculate and rebalance the kernel-vs-user priorities,
+ * and actually uninstall bp if necessary.
+ */
+ recalc_tprio();
+ balance_kernel_vs_user();
+ if (tsk == current)
+ switch_to_thread_hw_breakpoint(tsk);
+}
+
+/**
+ * unregister_user_hw_breakpoint - unregister a hardware breakpoint for user space
+ * @tsk: the task in whose memory space the breakpoint is registered
+ * @bp: the breakpoint structure to unregister
+ *
+ * Uninstalls and unregisters @bp.
+ */
+void unregister_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp)
+{
+ mutex_lock(&hw_breakpoint_mutex);
+ __unregister_user_hw_breakpoint(tsk, bp);
+ mutex_unlock(&hw_breakpoint_mutex);
+}
+
+/**
+ * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space
+ * @bp: the breakpoint structure to register
+ *
+ * This routine registers a breakpoint to be active at all times. It
+ * does not guarantee that the breakpoint will be allocated to a debug
+ * register immediately; there may be other higher-priority breakpoints
+ * registered which require the use of all the debug registers.
+ *
+ * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type,
+ * @bp->triggered and @bp->priority must be set properly before invocation
+ *
+ * Returns 1 if @bp is allocated to a debug register, 0 if @bp is
+ * registered but not allowed to be installed, otherwise a negative error
+ * code.
+ */
+int register_kernel_hw_breakpoint(struct hw_breakpoint *bp)
+{
+ int rc;
+ int pos;
+
+ bp->status = 0;
+ rc = validate_settings(bp, NULL);
+ if (rc)
+ return rc;
+
+ mutex_lock(&hw_breakpoint_mutex);
+
+ /* Insert bp in the kernel's list */
+ pos = insert_bp_in_list(bp, NULL, NULL);
+ arch_register_kernel_hw_breakpoint(bp);
+
+ /* Rebalance the priorities. This will install bp if it
+ * was allocated a debug register.
+ */
+ balance_kernel_vs_user();
+
+ /* Did bp get allocated to a debug register? We can tell from its
+ * position in the list. The number of registers allocated to
+ * kernel breakpoints is num_kbps; all the others are available for
+ * user breakpoints. If bp's position in the priority-ordered list
+ * is low enough, it will get a register.
+ */
+ if (pos < cur_kbpdata->num_kbps)
+ rc = 1;
+
+ mutex_unlock(&hw_breakpoint_mutex);
+ return rc;
+}
+EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint);
+
+/**
+ * unregister_kernel_hw_breakpoint - unregister a hardware breakpoint for kernel space
+ * @bp: the breakpoint structure to unregister
+ *
+ * Uninstalls and unregisters @bp.
+ */
+void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp)
+{
+ if (!bp->status)
+ return; /* Not registered */
+ mutex_lock(&hw_breakpoint_mutex);
+
+ /* Remove bp from the kernel's list */
+ remove_bp_from_list(bp, NULL, NULL);
+ arch_unregister_kernel_hw_breakpoint(bp);
+
+ /* Rebalance the priorities. This will uninstall bp if it
+ * was allocated a debug register.
+ */
+ balance_kernel_vs_user();
+
+ mutex_unlock(&hw_breakpoint_mutex);
+}
+EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint);

2009-01-29 07:55:03

by K.Prasad

Subject: [Patch 2/10] x86 architecture implementation of Hardware Breakpoint interfaces

This patch introduces two new files named hw_breakpoint.[ch] inside x86 specific
directories. They contain functions which help validate and serve requests for
using Hardware Breakpoint registers on x86 processors.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/Makefile | 2
arch/x86/kernel/hw_breakpoint.c | 464 ++++++++++++++++++++++++++++++++++++++++
include/asm-x86/hw_breakpoint.h | 135 +++++++++++
3 files changed, 600 insertions(+), 1 deletion(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/hw_breakpoint.c
@@ -0,0 +1,464 @@
+/*
+ * 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 <linux/kallsyms.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;
+}
+
+/*
+ * 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);
+}
+
+/*
+ * Store a breakpoint's encoded address, length, and type.
+ */
+static void arch_store_info(struct hw_breakpoint *bp)
+{
+ /*
+ * User-space requests will always have the address field populated
+ * For kernel-addresses, either the address or symbol name can be
+ * specified.
+ */
+ if (bp->info.address)
+ return;
+ bp->info.address = (unsigned long)kallsyms_lookup_name(bp->info.name);
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+static int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
+ unsigned int *align, struct task_struct *tsk)
+{
+ int ret = -EINVAL;
+
+ switch (bp->info.type) {
+
+ /* Ptrace-refactoring code
+ * For now, we'll allow instruction breakpoint only for user-space
+ * addresses
+ */
+ case HW_BREAKPOINT_EXECUTE:
+ if ((!arch_check_va_in_userspace(bp->info.address, tsk)) &&
+ bp->info.len != HW_BREAKPOINT_LEN_EXECUTE)
+ return ret;
+ break;
+ case HW_BREAKPOINT_WRITE:
+ break;
+ case HW_BREAKPOINT_RW:
+ break;
+ default:
+ return ret;
+ }
+
+ switch (bp->info.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);
+ }
+ return ret;
+}
+
+/*
+ * 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 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 = &cpu_data(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;
+ /*
+ * Presently we allow instruction breakpoints only in
+ * user-space when requested through ptrace.
+ */
+ case HW_BREAKPOINT_EXECUTE:
+ if (arch_check_va_in_userspace(bp->info.address,
+ current)) {
+ (bp->triggered)(bp, args->regs);
+ /* We'll return NOTIFY_DONE, do_debug will take care of the rest */
+ return NOTIFY_DONE;
+ }
+ }
+ }
+ }
+ /* 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"
+
Index: linux-hbkpt-lkml-29-rc2/include/asm-x86/hw_breakpoint.h
===================================================================
--- /dev/null
+++ linux-hbkpt-lkml-29-rc2/include/asm-x86/hw_breakpoint.h
@@ -0,0 +1,135 @@
+#ifndef _I386_HW_BREAKPOINT_H
+#define _I386_HW_BREAKPOINT_H
+
+#ifdef __KERNEL__
+#define __ARCH_HW_BREAKPOINT_H
+
+struct arch_hw_breakpoint {
+ char *name; /* Contains name of the symbol to set bkpt */
+ unsigned long address;
+ u8 len;
+ u8 type;
+} __attribute__((packed));
+
+#include <asm-generic/hw_breakpoint.h>
+
+/* HW breakpoint accessor routines */
+static inline const void *hw_breakpoint_get_kaddress(struct hw_breakpoint *bp)
+{
+ return (const void *) bp->info.address;
+}
+
+static inline const void __user *hw_breakpoint_get_uaddress
+ (struct hw_breakpoint *bp)
+{
+ return (const void __user *) bp->info.address;
+}
+
+static inline unsigned hw_breakpoint_get_len(struct hw_breakpoint *bp)
+{
+ return bp->info.len;
+}
+
+static inline unsigned hw_breakpoint_get_type(struct hw_breakpoint *bp)
+{
+ return bp->info.type;
+}
+
+/* Kernel symbol lookup routine for installing Data HW Breakpoint Address */
+static inline unsigned long hw_breakpoint_lookup_name(const char *name)
+{
+ return kallsyms_lookup_name(name);
+}
+
+/* Available HW breakpoint length encodings */
+#define HW_BREAKPOINT_LEN_1 0x40
+#define HW_BREAKPOINT_LEN_2 0x44
+#define HW_BREAKPOINT_LEN_4 0x4c
+#define HW_BREAKPOINT_LEN_EXECUTE 0x40
+
+/* Available HW breakpoint type encodings */
+#define HW_BREAKPOINT_EXECUTE 0x80 /* trigger on instruction execute */
+#define HW_BREAKPOINT_WRITE 0x81 /* trigger on memory write */
+#define HW_BREAKPOINT_RW 0x83 /* trigger on memory read or write */
+
+#define HB_NUM 4 /* Total number of available HW breakpoint registers */
+
+/* Per-thread HW breakpoint and debug register info */
+struct thread_hw_breakpoint {
+
+ /* utrace support */
+ struct list_head node; /* Entry in thread list */
+ struct list_head thread_bps; /* Thread's breakpoints */
+ struct hw_breakpoint *bps[HB_NUM]; /* Highest-priority bps */
+ unsigned long tdr[HB_NUM]; /* and their addresses */
+ int num_installed; /* Number of installed bps */
+ unsigned gennum; /* update-generation number */
+
+ /* Only the portions below are arch-specific */
+
+ /* ptrace support -- Note that vdr6 is stored directly in the
+ * thread_struct so that it is always available.
+ */
+ unsigned long vdr7; /* Virtualized DR7 */
+ struct hw_breakpoint vdr_bps[HB_NUM]; /* Breakpoints
+ representing virtualized debug registers 0 - 3 */
+ unsigned long tdr7; /* Thread's DR7 value */
+ unsigned long tkdr7; /* Thread + kernel DR7 value */
+};
+
+/* Kernel-space breakpoint data */
+struct kernel_bp_data {
+ unsigned gennum; /* Generation number */
+ int num_kbps; /* Number of kernel bps */
+ struct hw_breakpoint *bps[HB_NUM]; /* Loaded breakpoints */
+
+ /* Only the portions below are arch-specific */
+ unsigned long mkdr7; /* Masked kernel DR7 value */
+};
+
+/* Per-CPU debug register info */
+struct cpu_hw_breakpoint {
+ struct kernel_bp_data *cur_kbpdata; /* Current kbpdata[] entry */
+ struct task_struct *bp_task; /* The thread whose bps
+ are currently loaded in the debug registers */
+};
+
+/* Global info */
+static struct kernel_bp_data kbpdata[2]; /* Old and new settings */
+static int cur_kbpindex; /* Alternates 0, 1, ... */
+static struct kernel_bp_data *cur_kbpdata = &kbpdata[0];
+ /* Always equal to &kbpdata[cur_kbpindex] */
+
+static u8 tprio[HB_NUM]; /* Thread bp max priorities */
+static LIST_HEAD(kernel_bps); /* Kernel breakpoint list */
+static LIST_HEAD(thread_list); /* thread_hw_breakpoint list */
+
+/* Only the portions below are arch-specific */
+
+static unsigned long kdr7; /* Unmasked kernel DR7 value */
+
+/* Masks for the bits in DR7 related to kernel breakpoints, for various
+ * values of num_kbps. Entry n is the mask for when there are n kernel
+ * breakpoints, in debug registers 0 - (n-1). The DR_GLOBAL_SLOWDOWN bit
+ * (GE) is handled specially.
+ */
+static const unsigned long kdr7_masks[HB_NUM + 1] = {
+ 0x00000000,
+ 0x000f0003, /* LEN0, R/W0, G0, L0 */
+ 0x00ff000f, /* Same for 0,1 */
+ 0x0fff003f, /* Same for 0,1,2 */
+ 0xffff00ff /* Same for 0,1,2,3 */
+};
+
+/*
+ * Ptrace support: breakpoint trigger routine.
+ */
+
+int __register_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp);
+void __unregister_user_hw_breakpoint(struct task_struct *tsk,
+ struct hw_breakpoint *bp);
+
+#endif /* __KERNEL__ */
+#endif /* _I386_HW_BREAKPOINT_H */
+
Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/Makefile
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/Makefile
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/Makefile
@@ -35,7 +35,7 @@ obj-$(CONFIG_X86_64) += sys_x86_64.o x86
obj-$(CONFIG_X86_64) += syscall_64.o vsyscall_64.o
obj-y += bootflag.o e820.o
obj-y += pci-dma.o quirks.o i8237.o topology.o kdebugfs.o
-obj-y += alternative.o i8253.o pci-nommu.o
+obj-y += alternative.o i8253.o pci-nommu.o hw_breakpoint.o
obj-y += tsc.o io_delay.o rtc.o

obj-$(CONFIG_X86_TRAMPOLINE) += trampoline.o

2009-01-29 07:55:45

by K.Prasad

Subject: [Patch 3/10] Modifying generic debug exception to use virtual debug registers

This patch modifies the breakpoint exception handler code to use the abstract
register names.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/traps.c | 66 +++++++++++++++++-------------------------------
1 file changed, 24 insertions(+), 42 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/traps.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/traps.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/traps.c
@@ -570,10 +570,11 @@ 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.
@@ -581,61 +582,42 @@ 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
+ 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);

-clear_TF_reenable:
- set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
- regs->flags &= ~X86_EFLAGS_TF;
preempt_conditional_cli(regs);
- return;
}

#ifdef CONFIG_X86_64

2009-01-29 08:28:48

by K.Prasad

Subject: [Patch 4/10] Introduce virtual debug register in thread_struct and wrapper-routines around process related functions

This patch introduces virtual debug registers to used by the per-thread
structure ad wrapper routines to manage debug registers by process-related
functions.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/include/asm/debugreg.h | 27 +++++++++++++++++++++++++++
arch/x86/include/asm/processor.h | 10 +++-------
2 files changed, 30 insertions(+), 7 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/include/asm/debugreg.h
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/include/asm/debugreg.h
+++ linux-hbkpt-lkml-29-rc2/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 +69,29 @@
#define DR_LOCAL_SLOWDOWN (0x100) /* Local slow the pipeline */
#define DR_GLOBAL_SLOWDOWN (0x200) /* Global slow the pipeline */

+/*
+ * HW breakpoint additions
+ */
+#ifdef __KERNEL__
+
+/* 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-lkml-29-rc2/arch/x86/include/asm/processor.h
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/include/asm/processor.h
+++ linux-hbkpt-lkml-29-rc2/arch/x86/include/asm/processor.h
@@ -405,13 +405,9 @@ 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;

2009-01-29 08:29:25

by K.Prasad

Subject: [Patch 5/10] Use wrapper routines around debug registers in processor related functions

This patch enables the use of wrapper routines to access the debug/breakpoint
registers.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/smpboot.c | 3 +++
arch/x86/power/cpu_32.c | 16 +++-------------
arch/x86/power/cpu_64.c | 15 +++------------
3 files changed, 9 insertions(+), 25 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/power/cpu_32.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/power/cpu_32.c
+++ linux-hbkpt-lkml-29-rc2/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-hbkpt-lkml-29-rc2/arch/x86/power/cpu_64.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/power/cpu_64.c
+++ linux-hbkpt-lkml-29-rc2/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-hbkpt-lkml-29-rc2/arch/x86/kernel/smpboot.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/smpboot.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/smpboot.c
@@ -63,6 +63,7 @@
#include <asm/vmi.h>
#include <asm/genapic.h>
#include <asm/setup.h>
+#include <asm/debugreg.h>
#include <linux/mc146818rtc.h>

#include <mach_apic.h>
@@ -337,6 +338,7 @@ notrace static void __cpuinit start_seco
setup_secondary_clock();

wmb();
+ load_debug_registers();
cpu_idle();
}

@@ -1373,6 +1375,7 @@ void cpu_disable_common(void)
remove_cpu_from_maps(cpu);
unlock_vector_lock();
fixup_irqs();
+ disable_debug_registers();
}

int native_cpu_disable(void)

2009-01-29 08:30:13

by K.Prasad

Subject: [Patch 6/10] Use virtual debug registers in process/thread handling code

This patch enables the use of abstract/virtual debug registers in
process-handling routines.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/process_32.c | 43 +++++++++++++++++++++++++------------------
arch/x86/kernel/process_64.c | 41 ++++++++++++++++++++++++-----------------
2 files changed, 49 insertions(+), 35 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/process_32.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/process_32.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/process_32.c
@@ -60,6 +60,8 @@
#include <asm/idle.h>
#include <asm/syscalls.h>
#include <asm/ds.h>
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>

asmlinkage void ret_from_fork(void) __asm__("ret_from_fork");

@@ -231,6 +233,8 @@ 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;
@@ -251,6 +255,8 @@ 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);

ds_exit_thread(current);
}
@@ -259,14 +265,9 @@ 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);
+ if (unlikely(tsk->thread.hw_breakpoint_info))
+ flush_thread_hw_breakpoint(tsk);
/*
* Forget coprocessor state..
*/
@@ -310,7 +311,15 @@ 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);
@@ -329,11 +338,13 @@ int copy_thread(int nr, unsigned long cl
if (clone_flags & CLONE_SETTLS)
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);

ds_copy_thread(p, current);

@@ -435,16 +446,6 @@ __switch_to_xtra(struct task_struct *pre
else if (next->debugctlmsr != prev->debugctlmsr)
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 */
@@ -592,6 +593,12 @@ __switch_to(struct task_struct *prev_p,
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;
}
Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/process_64.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/process_64.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/process_64.c
@@ -52,6 +52,8 @@
#include <asm/proto.h>
#include <asm/ia32.h>
#include <asm/idle.h>
+#include <asm/debugreg.h>
+#include <asm/hw_breakpoint.h>
#include <asm/syscalls.h>
#include <asm/ds.h>

@@ -256,13 +258,9 @@ void flush_thread(void)
}
clear_tsk_thread_flag(tsk, TIF_DEBUG);

- 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));
+ if (unlikely(tsk->thread.hw_breakpoint_info))
+ flush_thread_hw_breakpoint(tsk);
/*
* Forget coprocessor state..
*/
@@ -282,6 +280,8 @@ void release_thread(struct task_struct *
BUG();
}
}
+ if (unlikely(me->thread.hw_breakpoint_info))
+ flush_thread_hw_breakpoint(me);
}

static inline void set_32bit_tls(struct task_struct *t, int tls, u32 addr)
@@ -337,13 +337,21 @@ int copy_thread(int nr, unsigned long cl

p->thread.fs = me->thread.fs;
p->thread.gs = me->thread.gs;
+ p->thread.hw_breakpoint_info = NULL;
+ p->thread.io_bitmap_ptr = NULL;

savesegment(gs, p->thread.gsindex);
savesegment(fs, p->thread.fsindex);
savesegment(es, p->thread.es);
savesegment(ds, p->thread.ds);

- if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
+ err = -ENOMEM;
+ if (unlikely(me->thread.hw_breakpoint_info)) {
+ if (copy_thread_hw_breakpoint(me, p, clone_flags))
+ goto out;
+ }
+
+if (unlikely(test_tsk_thread_flag(me, TIF_IO_BITMAP))) {
p->thread.io_bitmap_ptr = kmalloc(IO_BITMAP_BYTES, GFP_KERNEL);
if (!p->thread.io_bitmap_ptr) {
p->thread.io_bitmap_max = 0;
@@ -380,6 +388,9 @@ out:
kfree(p->thread.io_bitmap_ptr);
p->thread.io_bitmap_max = 0;
}
+ if (err)
+ flush_thread_hw_breakpoint(p);
+
return err;
}

@@ -482,16 +493,6 @@ static inline void __switch_to_xtra(stru
else if (next->debugctlmsr != prev->debugctlmsr)
update_debugctlmsr(next->debugctlmsr);

- if (test_tsk_thread_flag(next_p, TIF_DEBUG)) {
- loaddebug(next, 0);
- loaddebug(next, 1);
- loaddebug(next, 2);
- loaddebug(next, 3);
- /* no 4 and 5 */
- loaddebug(next, 6);
- loaddebug(next, 7);
- }
-
if (test_tsk_thread_flag(prev_p, TIF_NOTSC) ^
test_tsk_thread_flag(next_p, TIF_NOTSC)) {
/* prev and next are different */
@@ -514,6 +515,12 @@ static inline void __switch_to_xtra(stru
*/
memset(tss->io_bitmap, 0xff, prev->io_bitmap_max);
}
+ /*
+ * 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);
}

/*

2009-01-29 08:30:59

by K.Prasad

Subject: [Patch 7/10] Modify signal handling code to refrain from re-enabling HW Breakpoints

This patch disables re-enabling of Hardware Breakpoint registers through
the signal handling code. This is now done during
hw_breakpoint_handler().

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/signal.c | 9 ---------
1 file changed, 9 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/signal.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/signal.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/signal.c
@@ -814,15 +814,6 @@ 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) {
/*

2009-01-29 08:31:24

by K.Prasad

Subject: [Patch 8/10] Modify Ptrace routines to access breakpoint registers

This patch modifies the ptrace code to use the new wrapper routines around the
debug/breakpoint registers.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/ptrace.c | 228 +++++++++++++++++++++++++++++++----------------
1 file changed, 152 insertions(+), 76 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/ptrace.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/ptrace.c
+++ linux-hbkpt-lkml-29-rc2/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 +467,170 @@ 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;
+ bp->info.len = len;
+ bp->info.type = type;
+
+ bp->priority = HW_BREAKPOINT_PRIO_PTRACE;
+ if (rc == 0 && __register_user_hw_breakpoint(tsk,
+ bp) < 0)
+ break;
+ }
+ }

- case 6:
- if ((data & ~0xffffffffUL) != 0)
- return -EIO;
- child->thread.debugreg6 = data;
- break;
+ /* If anything above failed, restore the original settings */
+ if (i < HB_NUM) {
+ rc = -EIO;
+ data = old_dr7;
+ goto restore_settings;
+ }
+ return rc;
+}

- 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)
+/*
+ * 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);
+
+ bp->info.address = val;
+ rc = __register_user_hw_breakpoint(tsk, bp);
+ if (rc < 0) {
+ bp->info.address = old_addr;
+ __register_user_hw_breakpoint(tsk, bp);
+ }
+ } 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;
}

/*
@@ -872,7 +948,7 @@ 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;
@@ -890,7 +966,7 @@ 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;

2009-01-29 08:31:58

by K.Prasad

Subject: [Patch 9/10] Cleanup HW Breakpoint registers before kexec

This patch disables Hardware breakpoints before doing a 'kexec' on the machine.

Signed-off-by: K.Prasad <[email protected]>
Signed-off-by: Alan Stern <[email protected]>
---
arch/x86/kernel/machine_kexec_32.c | 2 ++
arch/x86/kernel/machine_kexec_64.c | 2 ++
2 files changed, 4 insertions(+)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/machine_kexec_32.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/machine_kexec_32.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/machine_kexec_32.c
@@ -25,6 +25,7 @@
#include <asm/desc.h>
#include <asm/system.h>
#include <asm/cacheflush.h>
+#include <asm/debugreg.h>

static void set_idt(void *newidt, __u16 limit)
{
@@ -202,6 +203,7 @@ 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-hbkpt-lkml-29-rc2/arch/x86/kernel/machine_kexec_64.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/machine_kexec_64.c
+++ linux-hbkpt-lkml-29-rc2/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);

2009-01-29 08:32:27

by K.Prasad

Subject: [Patch 10/10] Sample HW breakpoint over kernel data address

This patch introduces a sample kernel module to demonstrate the use of Hardware Breakpoint
feature. It places a breakpoint over the kernel variable 'pid_max' to monitor all
write operations and emits a function-backtrace when done.

Signed-off-by: K.Prasad <[email protected]>
---
samples/Kconfig | 6 ++
samples/Makefile | 3 -
samples/hw_breakpoint/Makefile | 1
samples/hw_breakpoint/data_breakpoint.c | 80 ++++++++++++++++++++++++++++++++
4 files changed, 89 insertions(+), 1 deletion(-)

Index: linux-hbkpt-lkml-29-rc2/samples/Kconfig
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/samples/Kconfig
+++ linux-hbkpt-lkml-29-rc2/samples/Kconfig
@@ -39,5 +39,11 @@ config SAMPLE_KRETPROBES
default m
depends on SAMPLE_KPROBES && KRETPROBES

+config SAMPLE_HW_BREAKPOINT
+ tristate "Build kernel hardware breakpoint examples -- loadable modules only"
+ depends on m
+ help
+ This builds kernel hardware breakpoint example modules.
+
endif # SAMPLES

Index: linux-hbkpt-lkml-29-rc2/samples/Makefile
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/samples/Makefile
+++ linux-hbkpt-lkml-29-rc2/samples/Makefile
@@ -1,3 +1,4 @@
# Makefile for Linux samples code

-obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/
+obj-$(CONFIG_SAMPLES) += markers/ kobject/ kprobes/ tracepoints/ \
+ hw_breakpoint/
Index: linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/Makefile
===================================================================
--- /dev/null
+++ linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_HW_BREAKPOINT) += data_breakpoint.o
Index: linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/data_breakpoint.c
===================================================================
--- /dev/null
+++ linux-hbkpt-lkml-29-rc2/samples/hw_breakpoint/data_breakpoint.c
@@ -0,0 +1,80 @@
+/*
+ * data_breakpoint.c - Sample HW Breakpoint file to watch kernel data address
+ *
+ * This file is a kernel module that places a breakpoint over 'pid_max' kernel
+ * variable using Hardware Breakpoint register. The corresponding handler which
+ * prints a backtrace is invoked everytime a write operation is performed on
+ * that variable.
+ *
+ * After inserting this module, invoke a write operation using
+ * 'echo <desired_value> > /proc/sys/kernel/pid_max'
+ * to find the function-call backtrace.
+ *
+ * Copyright (C) IBM Corporation, 2009
+ */
+#include <linux/module.h> /* Needed by all modules */
+#include <linux/kernel.h> /* Needed for KERN_INFO */
+#include <linux/init.h> /* Needed for the macros */
+
+#include <asm/hw_breakpoint.h>
+
+struct hw_breakpoint pid_max_hbkpt;
+
+void pid_max_hbkpt_installed(struct hw_breakpoint *temp, struct pt_regs
+ *temp_regs)
+{
+ printk(KERN_INFO "pid_max_hbkpt ENABLED\n");
+}
+
+void pid_max_hbkpt_uninstalled(struct hw_breakpoint *temp, struct
+ pt_regs * temp_regs)
+{
+ printk(KERN_INFO "pid_max_hbkpt DISABLED\n");
+}
+
+void pid_max_hbkpt_handler(struct hw_breakpoint *temp, struct pt_regs
+ *temp_regs)
+{
+ printk(KERN_INFO "pid_max value is changed\n");
+ dump_stack();
+ printk(KERN_INFO "Dump stack from pid_max_hbkpt_handler\n");
+}
+
+static int __init hw_break_module_init(void)
+{
+ int ret;
+
+#ifdef CONFIG_X86
+ pid_max_hbkpt.info.name = "pid_max";
+ pid_max_hbkpt.info.type = HW_BREAKPOINT_WRITE;
+ pid_max_hbkpt.info.len = HW_BREAKPOINT_LEN_4;
+ pid_max_hbkpt.priority = HW_BREAKPOINT_PRIO_NORMAL;
+
+ pid_max_hbkpt.installed = (void *)pid_max_hbkpt_installed;
+ pid_max_hbkpt.uninstalled = (void *)pid_max_hbkpt_uninstalled;
+ pid_max_hbkpt.triggered = (void *)pid_max_hbkpt_handler;
+#endif /* CONFIG_X86 */
+
+ ret = register_kernel_hw_breakpoint(&pid_max_hbkpt);
+
+ if (ret < 0) {
+ printk(KERN_INFO "Breakpoint registration failed\n");
+ return ret;
+ } else
+ printk(KERN_INFO "HW Breakpoint for pid_max write installed\n");
+
+ return 0;
+}
+
+static void __exit hw_break_module_exit(void)
+{
+ unregister_kernel_hw_breakpoint(&pid_max_hbkpt);
+ printk(KERN_INFO "HW Breakpoint for pid_max write uninstalled\n");
+}
+
+module_init(hw_break_module_init);
+module_exit(hw_break_module_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("K.Prasad");
+MODULE_DESCRIPTION("pid_max breakpoint");