Add support for serialized property contexts

This adds support for reading a serialized
/dev/__properties__/property_info file, which contains a
serialized trie that maps property names to the SELinux context to
which they belong.

Performance wise on walleye, this change reduces the start up cost in
libc from ~3000us to ~430us.  On a benchmark that calls
__system_property_find() for each property set on the system, it
reduces the time per iteration from ~650us to ~292us.

Bug: 36001741
Test: Boot bullhead, walleye, run unit tests
Test: Benchmark initialization and lookup performance

Change-Id: I0887a3a7da88eb51b6d1bd494fa5bce593423599

1 files changed, 171 insertions, 0 deletions

diff --git a/libc/system_properties/contexts_serialized.cpp b/libc/system_properties/contexts_serialized.cpp
new file mode 100644
index 000000000..117b5cf64
--- /dev/null
+++ b/libc/system_properties/contexts_serialized.cpp
@@ -0,0 +1,171 @@
+/*
+ * Copyright (C) 2017 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 "contexts_serialized.h"
+
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+#include <new>
+
+#include <async_safe/log.h>
+
+#include "private/bionic_prctl.h"
+#include "property_filename.h"
+
+bool ContextsSerialized::InitializeContextNodes() {
+  auto num_context_nodes = property_info_area_file_->num_contexts();
+  auto context_nodes_mmap_size = sizeof(ContextNode) * num_context_nodes;
+  // We want to avoid malloc in system properties, so we take an anonymous map instead (b/31659220).
+  void* const map_result = mmap(nullptr, context_nodes_mmap_size, PROT_READ | PROT_WRITE,
+                                MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+  if (map_result == MAP_FAILED) {
+    return false;
+  }
+
+  prctl(PR_SET_VMA, PR_SET_VMA_ANON_NAME, map_result, context_nodes_mmap_size,
+        "System property context nodes");
+
+  context_nodes_ = reinterpret_cast<ContextNode*>(map_result);
+  num_context_nodes_ = num_context_nodes;
+  context_nodes_mmap_size_ = context_nodes_mmap_size;
+
+  for (size_t i = 0; i < num_context_nodes; ++i) {
+    new (&context_nodes_[i]) ContextNode(property_info_area_file_->context(i));
+  }
+
+  return true;
+}
+
+bool ContextsSerialized::MapSerialPropertyArea(bool access_rw, bool* fsetxattr_failed) {
+  char filename[PROP_FILENAME_MAX];
+  int len = async_safe_format_buffer(filename, sizeof(filename), "%s/properties_serial",
+                                     property_filename);
+  if (len < 0 || len > PROP_FILENAME_MAX) {
+    serial_prop_area_ = nullptr;
+    return false;
+  }
+
+  if (access_rw) {
+    serial_prop_area_ =
+        prop_area::map_prop_area_rw(filename, "u:object_r:properties_serial:s0", fsetxattr_failed);
+  } else {
+    serial_prop_area_ = prop_area::map_prop_area(filename);
+  }
+  return serial_prop_area_;
+}
+
+bool ContextsSerialized::InitializeProperties() {
+  if (!property_info_area_file_.LoadDefaultPath()) {
+    return false;
+  }
+
+  if (!InitializeContextNodes()) {
+    FreeAndUnmap();
+    return false;
+  }
+
+  return true;
+}
+
+bool ContextsSerialized::Initialize(bool writable) {
+  if (!InitializeProperties()) {
+    return false;
+  }
+
+  if (writable) {
+    mkdir(property_filename, S_IRWXU | S_IXGRP | S_IXOTH);
+    bool open_failed = false;
+    bool fsetxattr_failed = false;
+
+    for (size_t i = 0; i < num_context_nodes_; ++i) {
+      if (!context_nodes_[i].Open(true, &fsetxattr_failed)) {
+        open_failed = true;
+      }
+    }
+    if (open_failed || !MapSerialPropertyArea(true, &fsetxattr_failed)) {
+      FreeAndUnmap();
+      return false;
+    }
+
+    return !fsetxattr_failed;
+  } else {
+    if (!MapSerialPropertyArea(false, nullptr)) {
+      FreeAndUnmap();
+      return false;
+    }
+  }
+  return true;
+}
+
+prop_area* ContextsSerialized::GetPropAreaForName(const char* name) {
+  uint32_t index;
+  property_info_area_file_->GetPropertyInfoIndexes(name, &index, nullptr);
+  if (index == ~0u || index >= num_context_nodes_) {
+    async_safe_format_log(ANDROID_LOG_ERROR, "libc", "Could not find context for property \"%s\"",
+                          name);
+    return nullptr;
+  }
+  auto* context_node = &context_nodes_[index];
+  if (!context_node->pa()) {
+    // We explicitly do not check no_access_ in this case because unlike the
+    // case of foreach(), we want to generate an selinux audit for each
+    // non-permitted property access in this function.
+    context_node->Open(false, nullptr);
+  }
+  return context_node->pa();
+}
+
+void ContextsSerialized::ForEach(void (*propfn)(const prop_info* pi, void* cookie), void* cookie) {
+  for (size_t i = 0; i < num_context_nodes_; ++i) {
+    if (context_nodes_[i].CheckAccessAndOpen()) {
+      context_nodes_[i].pa()->foreach (propfn, cookie);
+    }
+  }
+}
+
+void ContextsSerialized::ResetAccess() {
+  for (size_t i = 0; i < num_context_nodes_; ++i) {
+    context_nodes_[i].ResetAccess();
+  }
+}
+
+void ContextsSerialized::FreeAndUnmap() {
+  property_info_area_file_.Reset();
+  if (context_nodes_ != nullptr) {
+    for (size_t i = 0; i < num_context_nodes_; ++i) {
+      context_nodes_[i].Unmap();
+    }
+    munmap(context_nodes_, context_nodes_mmap_size_);
+    context_nodes_ = nullptr;
+  }
+  prop_area::unmap_prop_area(&serial_prop_area_);
+  serial_prop_area_ = nullptr;
+}