[Patch 03/12] x86 architecture implementation of Hardware Breakpoint interfaces

K.Prasad
2009-05-11T11:53:26Z

[-- Attachment #1: arch_x86_hwbkpt_03 --]
[-- Type: text/plain, Size: 10412 bytes --]

This patch introduces the arch-specific implementation of hw_breakpoint.c
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 <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
arch/x86/Kconfig | 1
arch/x86/kernel/Makefile | 2
arch/x86/kernel/hw_breakpoint.c | 358 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 360 insertions(+), 1 deletion(-)

Index: arch/x86/Kconfig
===================================================================
--- arch/x86/Kconfig.orig
+++ arch/x86/Kconfig
@@ -47,6 +47,7 @@ config X86
select HAVE_KERNEL_BZIP2
select HAVE_KERNEL_LZMA
select HAVE_ARCH_KMEMCHECK
+ select HAVE_HW_BREAKPOINT

config OUTPUT_FORMAT
string
Index: arch/x86/kernel/Makefile
===================================================================
--- arch/x86/kernel/Makefile.orig
+++ arch/x86/kernel/Makefile
@@ -36,7 +36,7 @@ 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
Index: arch/x86/kernel/hw_breakpoint.c
===================================================================
--- /dev/null
+++ arch/x86/kernel/hw_breakpoint.c
@@ -0,0 +1,358 @@
+/*
+ * 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) 2009 IBM Corporation
+ */
+
+/*
+ * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
+ * using the CPU's debug registers.
+ */
+
+#include <linux/irqflags.h>
+#include <linux/notifier.h>
+#include <linux/kallsyms.h>
+#include <linux/kprobes.h>
+#include <linux/percpu.h>
+#include <linux/kdebug.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/sched.h>
+#include <linux/init.h>
+#include <linux/smp.h>
+
+#include <asm/hw_breakpoint.h>
+#include <asm/processor.h>
+#include <asm/debugreg.h>
+
+/* Unmasked kernel DR7 value */
+static unsigned long kdr7;
+
+/*
+ * Masks for the bits corresponding to registers DR0 - DR3 in DR7 register.
+ * Used to clear and verify the status of bits corresponding to DR0 - DR3
+ */
+static const unsigned long dr7_masks[HB_NUM] = {
+ 0x000f0003, /* LEN0, R/W0, G0, L0 */
+ 0x00f0000c, /* LEN1, R/W1, G1, L1 */
+ 0x0f000030, /* LEN2, R/W2, G2, L2 */
+ 0xf00000c0 /* LEN3, R/W3, G3, L3 */
+};
+
+
+/*
+ * 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;
+}
+
+void arch_update_kernel_hw_breakpoints(void *unused)
+{
+ struct hw_breakpoint *bp;
+ int i, cpu = get_cpu();
+
+ /* Don't allow debug exceptions while we update the registers */
+ set_debugreg(0UL, 7);
+
+ /* Clear all kernel-space breakpoints in kdr7 */
+ kdr7 = 0;
+ for (i = hbp_kernel_pos; i < HB_NUM; i++) {
+ per_cpu(this_hbp_kernel[i], cpu) = bp = hbp_kernel[i];
+ if (bp) {
+ kdr7 |= encode_dr7(i, bp->info.len, bp->info.type);
+ set_debugreg(hbp_kernel[i]->info.address, i);
+ }
+ }
+
+ /* No need to set DR6. Update the debug registers with kernel-space
+ * breakpoint values from kdr7 and user-space requests from the
+ * current process
+ */
+ set_debugreg(kdr7 | current->thread.debugreg7, 7);
+ put_cpu_no_resched();
+}
+
+/*
+ * Install the thread breakpoints in their debug registers.
+ */
+void arch_install_thread_hw_breakpoint(struct task_struct *tsk)
+{
+ struct thread_struct *thread = &(tsk->thread);
+
+ switch (hbp_kernel_pos) {
+ case 4:
+ set_debugreg(thread->debugreg[3], 3);
+ case 3:
+ set_debugreg(thread->debugreg[2], 2);
+ case 2:
+ set_debugreg(thread->debugreg[1], 1);
+ case 1:
+ set_debugreg(thread->debugreg[0], 0);
+ default:
+ break;
+ }
+
+ /* No need to set DR6 */
+ set_debugreg((kdr7 | thread->debugreg7), 7);
+}
+
+/*
+ * Install the debug register values for just the kernel, no thread.
+ */
+void arch_uninstall_thread_hw_breakpoint()
+{
+ /* Clear the user-space portion of debugreg7 by setting only kdr7 */
+ set_debugreg(kdr7, 7);
+
+}
+
+static int get_hbp_len(u8 hbp_len)
+{
+ unsigned int len_in_bytes = 0;
+
+ switch (hbp_len) {
+ case HW_BREAKPOINT_LEN_1:
+ len_in_bytes = 1;
+ break;
+ case HW_BREAKPOINT_LEN_2:
+ len_in_bytes = 2;
+ break;
+ case HW_BREAKPOINT_LEN_4:
+ len_in_bytes = 4;
+ break;
+#ifdef CONFIG_X86_64
+ case HW_BREAKPOINT_LEN_8:
+ len_in_bytes = 8;
+ break;
+#endif
+ }
+ return len_in_bytes;
+}
+
+/*
+ * Check for virtual address in user space.
+ */
+int arch_check_va_in_userspace(unsigned long va, u8 hbp_len)
+{
+ unsigned int len;
+
+ len = get_hbp_len(hbp_len);
+
+ return (va <= TASK_SIZE - len);
+}
+
+/*
+ * Check for virtual address in kernel space.
+ */
+int arch_check_va_in_kernelspace(unsigned long va, u8 hbp_len)
+{
+ unsigned int len;
+
+ len = get_hbp_len(hbp_len);
+
+ return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
+}
+
+/*
+ * Store a breakpoint's encoded address, length, and type.
+ */
+static int 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.name)
+ bp->info.address = (unsigned long)
+ kallsyms_lookup_name(bp->info.name);
+ if (bp->info.address)
+ return 0;
+ return -EINVAL;
+}
+
+/*
+ * Validate the arch-specific HW Breakpoint register settings
+ */
+int arch_validate_hwbkpt_settings(struct hw_breakpoint *bp,
+ struct task_struct *tsk)
+{
+ unsigned int align;
+ 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,
+ bp->info.len)) &&
+ 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;
+#ifdef CONFIG_X86_64
+ case HW_BREAKPOINT_LEN_8:
+ align = 7;
+ break;
+#endif
+ default:
+ return ret;
+ }
+
+ if (bp->triggered)
+ ret = arch_store_info(bp);
+
+ if (ret < 0)
+ return ret;
+ /*
+ * 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, bp->info.len))
+ return -EFAULT;
+ } else {
+ if (!arch_check_va_in_kernelspace(bp->info.address,
+ bp->info.len))
+ return -EFAULT;
+ }
+ return 0;
+}
+
+void arch_update_user_hw_breakpoint(int pos, struct task_struct *tsk)
+{
+ struct thread_struct *thread = &(tsk->thread);
+ struct hw_breakpoint *bp = thread->hbp[pos];
+
+ thread->debugreg7 &= ~dr7_masks[pos];
+ if (bp) {
+ thread->debugreg[pos] = bp->info.address;
+ thread->debugreg7 |= encode_dr7(pos, bp->info.len,
+ bp->info.type);
+ } else
+ thread->debugreg[pos] = 0;
+}
+
+void arch_flush_thread_hw_breakpoint(struct task_struct *tsk)
+{
+ int i;
+ struct thread_struct *thread = &(tsk->thread);
+
+ thread->debugreg7 = 0;
+ for (i = 0; i < HB_NUM; i++)
+ thread->debugreg[i] = 0;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+int __kprobes hw_breakpoint_handler(struct die_args *args)
+{
+ int i, cpu, rc = NOTIFY_STOP;
+ struct hw_breakpoint *bp;
+ /* The DR6 value is stored in args->err */
+ unsigned long dr7, dr6 = args->err;
+
+ /* Do an early return if no trap bits are set in DR6 */
+ if ((dr6 & DR_TRAP_BITS) == 0)
+ return NOTIFY_DONE;
+
+ /* Lazy debug register switching */
+ if (!test_tsk_thread_flag(current, TIF_DEBUG))
+ switch_to_none_hw_breakpoint();
+
+ get_debugreg(dr7, 7);
+ /* Disable breakpoints during exception handling */
+ 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.debugreg6 &= ~DR_TRAP_BITS;
+ cpu = get_cpu();
+
+ /* 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 >= hbp_kernel_pos)
+ bp = per_cpu(this_hbp_kernel[i], cpu);
+ else {
+ bp = current->thread.hbp[i];
+ /* False alarm due to lazy DR switching */
+ if (!bp)
+ continue;
+ rc = NOTIFY_DONE;
+ }
+ (bp->triggered)(bp, args->regs);
+ }
+ if (dr6 & (~DR_TRAP_BITS))
+ rc = NOTIFY_DONE;
+
+ set_debugreg(dr7, 7);
+ put_cpu_no_resched();
+ return rc;
+}
+
+/*
+ * Handle debug exception notifications.
+ */
+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);
+}