1 files changed, 81 insertions, 0 deletions
diff --git a/libc/bionic/android_unsafe_frame_pointer_chase.cpp b/libc/bionic/android_unsafe_frame_pointer_chase.cpp
new file mode 100644
index 000000000..e25867b0e
--- /dev/null
+++ b/libc/bionic/android_unsafe_frame_pointer_chase.cpp
@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ *  * Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ *  * Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "platform/bionic/android_unsafe_frame_pointer_chase.h"
+
+#include "pthread_internal.h"
+#include "platform/bionic/mte.h"
+
+/*
+ * Implement fast stack unwinding for stack frames with frame pointers. Stores at most num_entries
+ * return addresses to buffer buf. Returns the number of available return addresses, which may be
+ * greater than num_entries.
+ *
+ * This function makes no guarantees about its behavior on encountering a frame built without frame
+ * pointers, except that it should not crash or enter an infinite loop, and that any frames prior to
+ * the frame built without frame pointers should be correct.
+ *
+ * This function is only meant to be used with memory safety tools such as sanitizers which need to
+ * take stack traces efficiently. Normal applications should use APIs such as libunwindstack or
+ * _Unwind_Backtrace.
+ */
+__attribute__((no_sanitize("address", "hwaddress"))) size_t android_unsafe_frame_pointer_chase(
+    uintptr_t* buf, size_t num_entries) {
+  // Disable MTE checks for the duration of this function, since we can't be sure that following
+  // next_frame pointers won't cause us to read from tagged memory. ASAN/HWASAN are disabled here
+  // for the same reason.
+  ScopedDisableMTE x;
+
+  struct frame_record {
+    uintptr_t next_frame, return_addr;
+  };
+
+  auto begin = reinterpret_cast<uintptr_t>(__builtin_frame_address(0));
+  uintptr_t end = __get_thread()->stack_top;
+
+  stack_t ss;
+  if (sigaltstack(nullptr, &ss) == 0 && (ss.ss_flags & SS_ONSTACK)) {
+    end = reinterpret_cast<uintptr_t>(ss.ss_sp) + ss.ss_size;
+  }
+
+  size_t num_frames = 0;
+  while (1) {
+    auto* frame = reinterpret_cast<frame_record*>(begin);
+    if (num_frames < num_entries) {
+      buf[num_frames] = frame->return_addr;
+    }
+    ++num_frames;
+    if (frame->next_frame < begin + sizeof(frame_record) || frame->next_frame >= end ||
+        frame->next_frame % sizeof(void*) != 0) {
+      break;
+    }
+    begin = frame->next_frame;
+  }
+
+  return num_frames;
+}