src/partition_alloc/slot_start_unittest.cc

// Copyright 2024 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#include "partition_alloc/partition_alloc_base/compiler_specific.h"
#include "partition_alloc/partition_alloc_for_testing.h"
#include "partition_alloc/partition_page.h"
#include "partition_alloc/use_death_tests.h"
#include "testing/gtest/include/gtest/gtest.h"

// These tests are default-disabled when PA passes through to a
// sanitizer, in which case the values returned from `Alloc()` are not
// managed by PartitionAlloc.
#if !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)

namespace partition_alloc::internal {
namespace {

constexpr PartitionOptions kOptions{};

class SlotStartTest : public testing::Test {
 protected:
  SlotStartTest()
      : allocator_(partition_alloc::PartitionAllocatorForTesting(kOptions)) {}

  partition_alloc::PartitionAllocatorForTesting allocator_;
};

TEST_F(SlotStartTest, SlotStartDoesntCrash) {
  void* buffer = allocator_.root()->Alloc(16, "");

  // `buffer` _is_ a slot start, so this must not crash.
  SlotStart::Checked(buffer, allocator_.root());

#if !PA_BUILDFLAG(DCHECKS_ARE_ON)
  // This is _not_ a slot start, but with enforcement off, this also
  // must not crash.
  SlotStart::Checked(PA_UNSAFE_TODO(static_cast<char*>(buffer) + 1),
                     allocator_.root());
#endif

  allocator_.root()->Free(buffer);
}

#if PA_USE_DEATH_TESTS() && PA_BUILDFLAG(DCHECKS_ARE_ON)
TEST_F(SlotStartTest, SlotStartCrashes) {
  void* buffer = allocator_.root()->Alloc(16, "");

  // `buffer + 1` is not a slot start, so this must crash.
  EXPECT_DEATH_IF_SUPPORTED(
      SlotStart::Checked(PA_UNSAFE_TODO(static_cast<char*>(buffer) + 1),
                         allocator_.root()),
      "");

  allocator_.root()->Free(buffer);
}

// In general, a `SlotStart` should not be constructed from a freed
// pointer, but this is only _really_ crashy when the freed pointer
// points to a direct map, which is decommitted immediately in
// `PartitionDirectUnmap()`. Normal buckets may or may not be subject
// to the same restriction, depending on the presence of the
// `MemoryReclaimer`.
TEST_F(SlotStartTest, SlotStartCrashesOnFreedDirectMap) {
  constexpr size_t kDirectMapSize = BucketIndexLookup::kMaxBucketSize + 1;
  void* buffer = allocator_.root()->Alloc(kDirectMapSize, "");
  ASSERT_TRUE(buffer);
  allocator_.root()->Free(buffer);

  // `buffer` was decommitted by the `Free()` above. We expect this
  // to crash.
  EXPECT_DEATH_IF_SUPPORTED(
      SlotStart::Checked(buffer, allocator_.root()).Untag(), "");
}
#endif  // PA_USE_DEATH_TESTS() && PA_BUILDFLAG(DCHECKS_ARE_ON)

}  // namespace
}  // namespace partition_alloc::internal

#endif  // !defined(MEMORY_TOOL_REPLACES_ALLOCATOR)