[RFC] [PATCH 2.6.37-rc5-tip 15/20] 15: x86: uprobes exception notifier for x86.

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

Provides a uprobes exception notifier for x86.  This uprobes_exception
notifier gets called in interrupt context and routes int3 and singlestep
exception when a uprobed process encounters a INT3 or a singlestep exception.

Signed-off-by: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 arch/x86/include/asm/uprobes.h |    3 +++
 arch/x86/kernel/signal.c       |   14 ++++++++++++++
 arch/x86/kernel/uprobes.c      |   29 +++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 0c9c8b6..bb5c03c 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -22,6 +22,7 @@
  *	Srikar Dronamraju
  *	Jim Keniston
  */
+#include <linux/notifier.h>
 
 typedef u8 uprobe_opcode_t;
 #define MAX_UINSN_BYTES 16
@@ -49,4 +50,6 @@ extern int pre_xol(struct uprobe *uprobe, struct pt_regs *regs);
 extern int post_xol(struct uprobe *uprobe, struct pt_regs *regs);
 extern void arch_uprobe_enable_sstep(struct pt_regs *regs);
 extern void arch_uprobe_disable_sstep(struct pt_regs *regs);
+extern int uprobes_exception_notify(struct notifier_block *self,
+				       unsigned long val, void *data);
 #endif	/* _ASM_UPROBES_H */
diff --git a/arch/x86/kernel/signal.c b/arch/x86/kernel/signal.c
index 4fd173c..0b06b94 100644
--- a/arch/x86/kernel/signal.c
+++ b/arch/x86/kernel/signal.c
@@ -20,6 +20,7 @@
 #include <linux/personality.h>
 #include <linux/uaccess.h>
 #include <linux/user-return-notifier.h>
+#include <linux/uprobes.h>
 
 #include <asm/processor.h>
 #include <asm/ucontext.h>
@@ -848,6 +849,19 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
 	if (thread_info_flags & _TIF_SIGPENDING)
 		do_signal(regs);
 
+	if (thread_info_flags & _TIF_UPROBE) {
+		clear_thread_flag(TIF_UPROBE);
+#ifdef CONFIG_X86_32
+		/*
+		 * On x86_32, do_notify_resume() gets called with
+		 * interrupts disabled. Hence enable interrupts if they
+		 * are still disabled.
+		 */
+		local_irq_enable();
+#endif
+		uprobe_notify_resume(regs);
+	}
+
 	if (thread_info_flags & _TIF_NOTIFY_RESUME) {
 		clear_thread_flag(TIF_NOTIFY_RESUME);
 		tracehook_notify_resume(regs);
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 9a0b8a9..c4239b3 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -568,3 +568,32 @@ void arch_uprobe_disable_sstep(struct pt_regs *regs)
 	clear_thread_flag(TIF_FORCED_TF);
 	regs->flags &= ~X86_EFLAGS_TF;
 }
+
+/*
+ * Wrapper routine for handling exceptions.
+ */
+int uprobes_exception_notify(struct notifier_block *self,
+				       unsigned long val, void *data)
+{
+	struct die_args *args = data;
+	struct pt_regs *regs = args->regs;
+	int ret = NOTIFY_DONE;
+
+	/* We are only interested in userspace traps */
+	if (regs && !user_mode_vm(regs))
+		return NOTIFY_DONE;
+
+	switch (val) {
+	case DIE_INT3:
+		/* Run your handler here */
+		if (uprobe_bkpt_notifier(regs))
+			ret = NOTIFY_STOP;
+		break;
+	case DIE_DEBUG:
+		if (uprobe_post_notifier(regs))
+			ret = NOTIFY_STOP;
+	default:
+		break;
+	}
+	return ret;
+}