[RFC Patch 4/10] Modify kprobe exception handler to recognise single-stepping by HW Breakpoint handler

K.Prasad
2009-01-22T14:06:04Z

This patch modifies the kprobe handler to help it recognise single-stepping by
the HW Breakpoint exception code. A per-cpu variable called 'sstep_reason' to
distinguish the source of single-step exceptions.

Signed-off-by: K.Prasad <prasad@linux.vnet.ibm.com>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
---
arch/x86/include/asm/debugreg.h | 29 +++++++++++++++++++++++++++++
arch/x86/include/asm/processor.h | 10 +++-------
arch/x86/kernel/kprobes.c | 6 ++++++
3 files changed, 38 insertions(+), 7 deletions(-)

Index: linux-hbkpt-lkml-29-rc2/arch/x86/kernel/kprobes.c
===================================================================
--- linux-hbkpt-lkml-29-rc2.orig/arch/x86/kernel/kprobes.c
+++ linux-hbkpt-lkml-29-rc2/arch/x86/kernel/kprobes.c
@@ -54,6 +54,7 @@
#include <asm/pgtable.h>
#include <asm/uaccess.h>
#include <asm/alternative.h>
+#include <asm/debugreg.h>

void jprobe_return_end(void);

@@ -518,6 +519,7 @@ static int __kprobes kprobe_handler(stru
kprobe_opcode_t *addr;
struct kprobe *p;
struct kprobe_ctlblk *kcb;
+ unsigned int *ssr;

addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
if (*addr != BREAKPOINT_INSTRUCTION) {
@@ -963,6 +965,10 @@ int __kprobes kprobe_exceptions_notify(s
ret = NOTIFY_STOP;
break;
case DIE_DEBUG:
+ /* We could be here due to single-stepping after a pre-handler
+ * execution of HW Breakpoint or kprobes. We determine the cause
+ * using the bitmask flag 'sstep_reason'.
+ */
if (post_kprobe_handler(args->regs))
ret = NOTIFY_STOP;
break;
Index: linux-hbkpt-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 +69,31 @@
#define DR_LOCAL_SLOWDOWN (0x100) /* Local slow the pipeline */
#define DR_GLOBAL_SLOWDOWN (0x200) /* Global slow the pipeline */

+/*
+ * HW breakpoint additions
+ */
+#ifdef __KERNEL__
+
+#define HB_NUM 4 /* Number of hardware breakpoints */
+
+/* For process management */
+void flush_thread_hw_breakpoint(struct task_struct *tsk);
+int copy_thread_hw_breakpoint(struct task_struct *tsk,
+ struct task_struct *child, unsigned long clone_flags);
+void dump_thread_hw_breakpoint(struct task_struct *tsk, int u_debugreg[8]);
+void switch_to_thread_hw_breakpoint(struct task_struct *tsk);
+
+/* For CPU management */
+void load_debug_registers(void);
+static inline void disable_debug_registers(void)
+{
+ set_debugreg(0UL, 7);
+}
+
+/* For use by ptrace */
+unsigned long thread_get_debugreg(struct task_struct *tsk, int n);
+int thread_set_debugreg(struct task_struct *tsk, int n, unsigned long val);
+
+#endif /* __KERNEL__ */
+
#endif /* _ASM_X86_DEBUGREG_H */
Index: linux-hbkpt-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;