ptrace/x86: flush_ptrace_hw_breakpoint() shoule clear the virtual debug registers

flush_ptrace_hw_breakpoint() destroys the counters set by ptrace, but
"leaks" ->debugreg6 and ->ptrace_dr7.

The problem is minor, but still it doesn't look right and flush_thread()
did this until 66cb5917 ("hw-breakpoints: use the new wrapper routines to
access debug registers in process/thread code").  Now that PTRACE_DETACH
does flush_ too this makes even more sense.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jan Kratochvil <jan.kratochvil@redhat.com>
Cc: Michael Neuling <mikey@neuling.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Prasad <prasad@linux.vnet.ibm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c
index 02f07634d265ea0a840892b5bafbd554197644b8..f66ff162dce864a5db31949969271049396f8552 100644 (file)
--- a/arch/x86/kernel/hw_breakpoint.c
+++ b/arch/x86/kernel/hw_breakpoint.c
@@ -393,6 +393,9 @@ void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
                unregister_hw_breakpoint(t->ptrace_bps[i]);
                t->ptrace_bps[i] = NULL;
        }
+
+       t->debugreg6 = 0;
+       t->ptrace_dr7 = 0;
 }
 
 void hw_breakpoint_restore(void)