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

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.

Cc: <stable@vger.kernel.org>
Signed-off-by: John Blackwood <john.blackwood@ccur.com>
[will: added comment to justify why this is in the arch code]
Signed-off-by: Will Deacon <will.deacon@arm.com>

diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c
index 1971f49..ff7f132 100644 (file)
--- a/arch/arm64/kernel/ptrace.c
+++ b/arch/arm64/kernel/ptrace.c
@@ -58,6 +58,12 @@
  */
 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