[3.16.y-ckt stable] Patch "arm64: Clear out any singlestep state on a ptrace detach operation" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    arm64: Clear out any singlestep state on a ptrace detach operation

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

    http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt24.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

---8<------------------------------------------------------------

>From cb220afba199ee871af8572e9847252761b2afe7 Mon Sep 17 00:00:00 2001
From: John Blackwood <john.blackwood at ccur.com>
Date: Mon, 7 Dec 2015 11:50:34 +0000
Subject: arm64: Clear out any singlestep state on a ptrace detach operation

commit 5db4fd8c52810bd9740c1240ebf89223b171aa70 upstream.

Make sure to clear out any ptrace singlestep state when a ptrace(2)
PTRACE_DETACH call is made on arm64 systems.

Otherwise, the previously ptraced task will die off with a SIGTRAP
signal if the debugger just previously singlestepped the ptraced task.

Signed-off-by: John Blackwood <john.blackwood at ccur.com>
[will: added comment to justify why this is in the arch code]
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 arch/arm64/kernel/ptrace.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 167c5edecad4..d2b9a3f7457d 100644
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -55,6 +55,12 @@
  */
 void ptrace_disable(struct task_struct *child)
 {
+	/*
+	 * This would be better off in core code, but PTRACE_DETACH has
+	 * grown its fair share of arch-specific worts and changing it
+	 * is likely to cause regressions on obscure architectures.
+	 */
+	user_disable_single_step(child);
 }

 #ifdef CONFIG_HAVE_HW_BREAKPOINT