Patch "arm64: kernel: Fix unmasked debug exceptions when restoring mdscr_el1" has been added to the 4.7-stable tree

This is a note to let you know that I've just added the patch titled

arm64: kernel: Fix unmasked debug exceptions when restoring mdscr_el1

to the 4.7-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
arm64-kernel-fix-unmasked-debug-exceptions-when-restoring-mdscr_el1.patch
and it can be found in the queue-4.7 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: James Morse <[email protected]>
Date: Fri, 26 Aug 2016 16:03:42 +0100
Subject: arm64: kernel: Fix unmasked debug exceptions when restoring mdscr_el1

From: James Morse <[email protected]>

commit 744c6c37cc18705d19e179622f927f5b781fe9cc upstream.

Changes to make the resume from cpu_suspend() code behave more like secondary boot caused debug exceptions to be unmasked early by __cpu_setup(). We then go on to restore mdscr_el1 in cpu_do_resume(), potentially taking break or watch points based on uninitialised registers.

Mask debug exceptions in cpu_do_resume(), which is specific to resume from cpu_suspend(). Debug exceptions will be restored to their original state by local_dbg_restore() in cpu_suspend(), which runs after hw_breakpoint_restore() has re-initialised the other registers.

---
 arch/arm64/mm/proc.S |    9 +++++++++
 1 file changed, 9 insertions(+)

@@ -100,7 +100,16 @@ ENTRY(cpu_do_resume)
 
 	msr	tcr_el1, x8
 	msr	vbar_el1, x9
+
+	/*
+	 * __cpu_setup() cleared MDSCR_EL1.MDE and friends, before unmasking
+	 * debug exceptions. By restoring MDSCR_EL1 here, we may take a debug
+	 * exception. Mask them until local_dbg_restore() in cpu_suspend()
+	 * resets them.
+	 */
+	disable_dbg
 	msr	mdscr_el1, x10
+
 	msr	sctlr_el1, x12
 	/*
 	 * Restore oslsr_el1 by writing oslar_el1

Patches currently in stable-queue which might be from [email protected] are

queue-4.7/arm64-kernel-fix-unmasked-debug-exceptions-when-restoring-mdscr_el1.patch