ptrace: flush breakpoints

Unfortunately the kernel doesn't flush hw breakpoints on
detaching ptrace. If a breakpoint is triggered without ptrace, it
will be killed by SIGTRAP.

Reported-by: Mr Jenkins
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

arch/aarch64/include/asm/restorer.h

@@ -113,4 +113,9 @@ static inline int ptrace_set_breakpoint(pid_t pid, void *addr)
 	return 0;
 }
 
+static inline int ptrace_flush_breakpoints(pid_t pid)
+{
+	return 0;
+}
+
 #endif

arch/arm/include/asm/restorer.h

@@ -155,4 +155,9 @@ static inline int ptrace_set_breakpoint(pid_t pid, void *addr)
 	return 0;
 }
 
+static inline int ptrace_flush_breakpoints(pid_t pid)
+{
+	return 0;
+}
+
 #endif

arch/x86/crtools.c

@@ -540,3 +540,16 @@ int ptrace_set_breakpoint(pid_t pid, void *addr)
 	return 1;
 }
 
+int ptrace_flush_breakpoints(pid_t pid)
+{
+	/* Disable the breakpoint */
+	if (ptrace(PTRACE_POKEUSER, pid,
+			offsetof(struct user, u_debugreg[DR_CONTROL]),
+			0)) {
+		pr_err("Unable to disable the breakpoint\n");
+		return -1;
+	}
+
+	return 0;
+}
+

arch/x86/include/asm/restorer.h

@@ -146,6 +146,7 @@ int sigreturn_prep_fpu_frame(struct rt_sigframe *sigframe, fpu_state_t *fpu_stat
 static inline void restore_tls(tls_t *ptls) { (void)ptls; }
 
 int ptrace_set_breakpoint(pid_t pid, void *addr);
+int ptrace_flush_breakpoints(pid_t pid);
 
 
 #endif

cr-restore.c

@@ -1599,6 +1599,18 @@ static int attach_to_tasks(bool root_seized, enum trace_flags *flag)
 	return 0;
 }
 
+static int clear_breakpoints()
+{
+	struct pstree_item *item;
+	int ret = 0, i;
+
+	for_each_pstree_item(item)
+		for (i = 0; i < item->nr_threads; i++)
+			ret |= ptrace_flush_breakpoints(item->threads[i].real);
+
+	return ret;
+}
+
 static void finalize_restore(int status)
 {
 	struct pstree_item *item;
@@ -1775,6 +1787,9 @@ static int restore_root_task(struct pstree_item *init)
 		ret = parasite_stop_on_syscall(task_entries->nr_threads,
 						__NR_rt_sigreturn, flag);
 
+	if (clear_breakpoints())
+		pr_err("Unable to flush breakpoints\n");
+
 	/*
 	 * finalize_restore() always detaches from processes and
 	 * they continue run through sigreturn.

parasite-syscall.c

@@ -890,6 +890,9 @@ static int parasite_fini_seized(struct parasite_ctl *ctl)
 	if (parasite_stop_on_syscall(1, __NR_rt_sigreturn, flag))
 		return -1;
 
+	if (ptrace_flush_breakpoints(pid))
+		return -1;
+
 	/*
 	 * All signals are unblocked now. The kernel notifies about leaving
 	 * syscall before starting to deliver signals. All parasite code are