1 files changed, 9 insertions, 1 deletions
diff --git a/linux-user/signal.c b/linux-user/signal.c
index e2d55fff97..9d980456ec 100644
--- a/linux-user/signal.c
+++ b/linux-user/signal.c
@@ -636,8 +636,16 @@ static void host_signal_handler(int host_signum, siginfo_t *info,
      * code in case the guest code provokes one in the window between
      * now and it getting out to the main loop. Signals will be
      * unblocked again in process_pending_signals().
+     *
+     * WARNING: we cannot use sigfillset() here because the uc_sigmask
+     * field is a kernel sigset_t, which is much smaller than the
+     * libc sigset_t which sigfillset() operates on. Using sigfillset()
+     * would write 0xff bytes off the end of the structure and trash
+     * data on the struct.
+     * We can't use sizeof(uc->uc_sigmask) either, because the libc
+     * headers define the struct field with the wrong (too large) type.
      */
-    sigfillset(&uc->uc_sigmask);
+    memset(&uc->uc_sigmask, 0xff, SIGSET_T_SIZE);
     sigdelset(&uc->uc_sigmask, SIGSEGV);
     sigdelset(&uc->uc_sigmask, SIGBUS);