[CRIU] [PATCH] ptrace: flush breakpoints

[Andrey Vagin]

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 at openvz.org>
---
 arch/aarch64/include/asm/restorer.h |  5 +++++
 arch/arm/include/asm/restorer.h     |  5 +++++
 arch/x86/crtools.c                  | 13 +++++++++++++
 arch/x86/include/asm/restorer.h     |  1 +
 cr-restore.c                        | 15 +++++++++++++++
 parasite-syscall.c                  |  3 +++
 6 files changed, 42 insertions(+)

diff --git a/arch/aarch64/include/asm/restorer.h b/arch/aarch64/include/asm/restorer.h
index 53c3847..61e8576 100644
--- a/arch/aarch64/include/asm/restorer.h
+++ b/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
diff --git a/arch/arm/include/asm/restorer.h b/arch/arm/include/asm/restorer.h
index 36ce4e9..8acb2d3 100644
--- a/arch/arm/include/asm/restorer.h
+++ b/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
diff --git a/arch/x86/crtools.c b/arch/x86/crtools.c
index 1248975..cbbcb9d 100644
--- a/arch/x86/crtools.c
+++ b/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;
+}
+
diff --git a/arch/x86/include/asm/restorer.h b/arch/x86/include/asm/restorer.h
index 00d4977..70199fb 100644
--- a/arch/x86/include/asm/restorer.h
+++ b/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
diff --git a/cr-restore.c b/cr-restore.c
index 809564b..7141c6c 100644
--- a/cr-restore.c
+++ b/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.
diff --git a/parasite-syscall.c b/parasite-syscall.c
index 37e9db0..9102b23 100644
--- a/parasite-syscall.c
+++ b/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
-- 
1.9.3