linux-kernel - [PATCH 3.16.y-ckt 031/180] arm64: Clear out any singlestep state on a ptrace detach operation

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Message-Id: <1454538786-12215-32-git-send-email-luis.henriques@canonical.com>
Date:	Wed,  3 Feb 2016 22:30:37 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	John Blackwood <john.blackwood@...r.com>,
	Will Deacon <will.deacon@....com>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 031/180] arm64: Clear out any singlestep state on a ptrace detach operation

3.16.7-ckt24 -stable review patch.  If anyone has any objections, please let me know.

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

From: John Blackwood <john.blackwood@...r.com>

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@...r.com>
[will: added comment to justify why this is in the arch code]
Signed-off-by: Will Deacon <will.deacon@....com>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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