[BUGFIX][PATCH -rc/-mm] prevent kprobes from catching spurious page faults

[Masami Hiramatsu <mhiramat@redhat.com>]

Prevent kprobes from catching spurious faults which will cause infinite
recursive page-fault and memory corruption by stack overflow.

Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
---
 This patch solves memory corruption bug which I reported last week.
 http://lkml.org/lkml/2009/1/27/428
 Since 2.6.28 kernel also has same bug, I think it should be applied
 to 2.6.28.y too.

 Thanks,

 arch/x86/mm/fault.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/mm/fault.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/fault.c
+++ linux-2.6/arch/x86/mm/fault.c
@@ -603,8 +603,6 @@ void __kprobes do_page_fault(struct pt_r

 	si_code = SEGV_MAPERR;

-	if (notify_page_fault(regs))
-		return;
 	if (unlikely(kmmio_fault(regs, address)))
 		return;

@@ -634,6 +632,9 @@ void __kprobes do_page_fault(struct pt_r
 		if (spurious_fault(address, error_code))
 			return;

+		/* kprobes don't want to hook the spurious faults. */
+		if (notify_page_fault(regs))
+			return;
 		/*
 		 * Don't take the mm semaphore here. If we fixup a prefetch
 		 * fault we could otherwise deadlock.
@@ -641,6 +642,9 @@ void __kprobes do_page_fault(struct pt_r
 		goto bad_area_nosemaphore;
 	}

+	/* kprobes don't want to hook the spurious faults. */
+	if (notify_page_fault(regs))
+		return;

 	/*
 	 * It's safe to allow irq's after cr2 has been saved and the

-- 
Masami Hiramatsu

Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division

e-mail: mhiramat@redhat.com