[PATCH v5 3.1.0-rc4-tip 13/26] x86: define a x86 specific exception notifier.

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

Uprobes uses notifier mechanism to get in control when an application
encounters a breakpoint 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 |    4 ++++
 arch/x86/kernel/signal.c       |   14 ++++++++++++++
 arch/x86/kernel/uprobes.c      |   29 +++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 0 deletions(-)

diff --git a/arch/x86/include/asm/uprobes.h b/arch/x86/include/asm/uprobes.h
index 35ac9d7..7d9d0a5 100644
--- a/arch/x86/include/asm/uprobes.h
+++ b/arch/x86/include/asm/uprobes.h
@@ -23,6 +23,8 @@
  *	Jim Keniston
  */
 
+#include <linux/notifier.h>
+
 typedef u8 uprobe_opcode_t;
 #define MAX_UINSN_BYTES 16
 #define UPROBES_XOL_SLOT_BYTES	128	/* to keep it cache aligned */
@@ -40,4 +42,6 @@ struct uprobe_arch_info {};
 struct uprobe;
 extern int analyze_insn(struct task_struct *tsk, struct uprobe *uprobe);
 extern void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr);
+extern int uprobe_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 54ddaeb..97fac33 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>
@@ -820,6 +821,19 @@ do_notify_resume(struct pt_regs *regs, void *unused, __u32 thread_info_flags)
 		mce_notify_process();
 #endif /* CONFIG_X86_64 && CONFIG_X86_MCE */
 
+	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);
+	}
+
 	/* deal with pending signal delivery */
 	if (thread_info_flags & _TIF_SIGPENDING)
 		do_signal(regs);
diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index e1c1dfe..8ec759a 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c
@@ -393,3 +393,32 @@ void set_instruction_pointer(struct pt_regs *regs, unsigned long vaddr)
 {
 	regs->ip = vaddr;
 }
+
+/*
+ * Wrapper routine for handling exceptions.
+ */
+int uprobe_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;
+}

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