This is a note to let you know that I've just added the patch titled
arm64: debug: don't re-enable debug exceptions on return from el1_dbg
to the 3.16-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-debug-don-t-re-enable-debug-exceptions-on-return-from-el1_dbg.patch
and it can be found in the queue-3.16 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 1059c6bf8534acda249e7e65c81e7696fb074dc1 Mon Sep 17 00:00:00 2001
From: Will Deacon <will.deacon@xxxxxxx>
Date: Mon, 22 Sep 2014 11:19:04 +0100
Subject: arm64: debug: don't re-enable debug exceptions on return from el1_dbg
From: Will Deacon <will.deacon@xxxxxxx>
commit 1059c6bf8534acda249e7e65c81e7696fb074dc1 upstream.
When returning from a debug exception taken from EL1, we unmask debug
exceptions after handling the exception. This is crucial for debug
exceptions taken from EL0, so that any kernel work on the ret_to_user
path can be debugged by kgdb.
However, when returning back to EL1 the only thing left to do is to
restore the original register state before the exception return. If
single-step has been enabled by the debug exception handler, we will
get stuck in an infinite debug exception loop, since we will take the
step exception as soon as we unmask debug exceptions.
This patch avoids unmasking debug exceptions on the debug exception
return path when the exception was taken from EL1.
Fixes: 2a2830703a23 (arm64: debug: avoid accessing mdscr_el1 on fault paths where possible)
Reported-by: David Long <dave.long@xxxxxxxxxx>
Reported-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/arm64/kernel/entry.S | 1 -
1 file changed, 1 deletion(-)
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -298,7 +298,6 @@ el1_dbg:
mrs x0, far_el1
mov x2, sp // struct pt_regs
bl do_debug_exception
- enable_dbg
kernel_exit 1
el1_inv:
// TODO: add support for undefined instructions in kernel mode
Patches currently in stable-queue which might be from will.deacon@xxxxxxx are
queue-3.16/arm64-debug-don-t-re-enable-debug-exceptions-on-return-from-el1_dbg.patch
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