Allocate a small guard region around the shadow call stack.

This lets us do two things:

1) Make setjmp and longjmp compatible with shadow call stack.
   To avoid leaking the shadow call stack address into memory, only the
   lower log2(SCS_SIZE) bits of x18 are stored to jmp_buf. This requires
   allocating an additional guard page so that we're guaranteed to be
   able to allocate a sufficiently aligned SCS.

2) SCS overflow detection. Overflows now result in a SIGSEGV instead
   of corrupting the allocation that comes after it.

Change-Id: I04d6634f96162bf625684672a87fba8b402b7fd1
Test: bionic-unit-tests

1 files changed, 39 insertions, 0 deletions

diff --git a/tests/scs_test.cpp b/tests/scs_test.cpp
new file mode 100644
index 000000000..24cb347bb
--- /dev/null
+++ b/tests/scs_test.cpp
@@ -0,0 +1,39 @@
+/*
+ * Copyright (C) 2018 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if __has_feature(shadow_call_stack)
+
+#include <gtest/gtest.h>
+
+#include "private/bionic_constants.h"
+
+int recurse2(int count);
+
+__attribute__((weak, noinline)) int recurse1(int count) {
+  if (count != 0) return recurse2(count - 1) + 1;
+  return 0;
+}
+
+__attribute__((weak, noinline)) int recurse2(int count) {
+  if (count != 0) return recurse1(count - 1) + 1;
+  return 0;
+}
+
+TEST(scs_test, stack_overflow) {
+  ASSERT_EXIT(recurse1(SCS_SIZE), testing::KilledBySignal(SIGSEGV), "");
+}
+
+#endif