// Copyright 2018 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_MEMORY_PLATFORM_SHARED_MEMORY_REGION_H_
#define BASE_MEMORY_PLATFORM_SHARED_MEMORY_REGION_H_

#include "base/base_export.h"
#include "base/containers/span.h"
#include "base/gtest_prod_util.h"
#include "base/memory/platform_shared_memory_handle.h"
#include "base/memory/shared_memory_mapper.h"
#include "base/unguessable_token.h"
#include "build/build_config.h"
#include "third_party/abseil-cpp/absl/types/optional.h"

#include <stdint.h>

#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
namespace content {
class SandboxIPCHandler;
}
#endif

namespace base {
namespace subtle {

// Implementation class for shared memory regions.
//
// This class does the following:
//
// - Wraps and owns a shared memory region platform handle.
// - Provides a way to allocate a new region of platform shared memory of given
//   size.
// - Provides a way to create mapping of the region in the current process'
//   address space, under special access-control constraints (see Mode).
// - Provides methods to help transferring the handle across process boundaries.
// - Holds a 128-bit unique identifier used to uniquely identify the same
//   kernel region resource across processes (used for memory tracking).
// - Has a method to retrieve the region's size in bytes.
//
// IMPORTANT NOTE: Users should never use this directly, but
// ReadOnlySharedMemoryRegion, WritableSharedMemoryRegion or
// UnsafeSharedMemoryRegion since this is an implementation class.
class BASE_EXPORT PlatformSharedMemoryRegion {
 public:
  // Permission mode of the platform handle. Each mode corresponds to one of the
  // typed shared memory classes:
  //
  // * ReadOnlySharedMemoryRegion: A region that can only create read-only
  // mappings.
  //
  // * WritableSharedMemoryRegion: A region that can only create writable
  // mappings. The region can be demoted to ReadOnlySharedMemoryRegion without
  // the possibility of promoting back to writable.
  //
  // * UnsafeSharedMemoryRegion: A region that can only create writable
  // mappings. The region cannot be demoted to ReadOnlySharedMemoryRegion.
  enum class Mode {
    kReadOnly,  // ReadOnlySharedMemoryRegion
    kWritable,  // WritableSharedMemoryRegion
    kUnsafe,    // UnsafeSharedMemoryRegion
    kMaxValue = kUnsafe
  };

  // Errors that can occur during Shared Memory construction.
  // These match tools/metrics/histograms/enums.xml.
  // This enum is append-only.
  enum class CreateError {
    SUCCESS = 0,
    SIZE_ZERO = 1,
    SIZE_TOO_LARGE = 2,
    INITIALIZE_ACL_FAILURE = 3,
    INITIALIZE_SECURITY_DESC_FAILURE = 4,
    SET_SECURITY_DESC_FAILURE = 5,
    CREATE_FILE_MAPPING_FAILURE = 6,
    REDUCE_PERMISSIONS_FAILURE = 7,
    ALREADY_EXISTS = 8,
    ALLOCATE_FILE_REGION_FAILURE = 9,
    FSTAT_FAILURE = 10,
    INODES_MISMATCH = 11,
    GET_SHMEM_TEMP_DIR_FAILURE = 12,
    kMaxValue = GET_SHMEM_TEMP_DIR_FAILURE
  };

#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
  // Structure to limit access to executable region creation.
  struct ExecutableRegion {
   private:
    // Creates a new shared memory region the unsafe mode (writable and not and
    // convertible to read-only), and in addition marked executable. A ScopedFD
    // to this region is returned. Any any mapping will have to be done
    // manually, including setting executable permissions if necessary
    //
    // This is only used to support sandbox_ipc_linux.cc, and should not be used
    // anywhere else in chrome. This is restricted via AllowCreateExecutable.
    // TODO(crbug.com/982879): remove this when NaCl is unshipped.
    //
    // Returns an invalid ScopedFD if the call fails.
    static ScopedFD CreateFD(size_t size);

    friend class content::SandboxIPCHandler;
  };
#endif

  // The minimum alignment in bytes that any mapped address produced by Map()
  // and MapAt() is guaranteed to have.
  enum { kMapMinimumAlignment = 32 };

  // Creates a new PlatformSharedMemoryRegion with corresponding mode and size.
  // Creating in kReadOnly mode isn't supported because then there will be no
  // way to modify memory content.
  static PlatformSharedMemoryRegion CreateWritable(size_t size);
  static PlatformSharedMemoryRegion CreateUnsafe(size_t size);

  // Returns a new PlatformSharedMemoryRegion that takes ownership of the
  // |handle|. All parameters must be taken from another valid
  // PlatformSharedMemoryRegion instance, e.g. |size| must be equal to the
  // actual region size as allocated by the kernel.
  // Closes the |handle| and returns an invalid instance if passed parameters
  // are invalid.
  static PlatformSharedMemoryRegion Take(
      ScopedPlatformSharedMemoryHandle handle,
      Mode mode,
      size_t size,
      const UnguessableToken& guid);
#if BUILDFLAG(IS_POSIX) && !BUILDFLAG(IS_ANDROID) && !BUILDFLAG(IS_APPLE)
  // Specialized version of Take() for POSIX that takes only one file descriptor
  // instead of pair. Cannot be used with kWritable |mode|.
  static PlatformSharedMemoryRegion Take(ScopedFD handle,
                                         Mode mode,
                                         size_t size,
                                         const UnguessableToken& guid);
#endif

  // Default constructor initializes an invalid instance, i.e. an instance that
  // doesn't wrap any valid platform handle.
  PlatformSharedMemoryRegion();

  // Move operations are allowed.
  PlatformSharedMemoryRegion(PlatformSharedMemoryRegion&&);
  PlatformSharedMemoryRegion& operator=(PlatformSharedMemoryRegion&&);
  PlatformSharedMemoryRegion(const PlatformSharedMemoryRegion&) = delete;
  PlatformSharedMemoryRegion& operator=(const PlatformSharedMemoryRegion&) =
      delete;

  // Destructor closes the platform handle. Does nothing if the handle is
  // invalid.
  ~PlatformSharedMemoryRegion();

  // Passes ownership of the platform handle to the caller. The current instance
  // becomes invalid. It's the responsibility of the caller to close the
  // handle. If the current instance is invalid, ScopedPlatformHandle will also
  // be invalid.
  [[nodiscard]] ScopedPlatformSharedMemoryHandle PassPlatformHandle();

  // Returns the platform handle. The current instance keeps ownership of this
  // handle.
  PlatformSharedMemoryHandle GetPlatformHandle() const;

  // Whether the platform handle is valid.
  bool IsValid() const;

  // Duplicates the platform handle and creates a new PlatformSharedMemoryRegion
  // with the same |mode_|, |size_| and |guid_| that owns this handle. Returns
  // invalid region on failure, the current instance remains valid.
  // Can be called only in kReadOnly and kUnsafe modes, CHECK-fails if is
  // called in kWritable mode.
  PlatformSharedMemoryRegion Duplicate() const;

  // Converts the region to read-only. Returns whether the operation succeeded.
  // Makes the current instance invalid on failure. Can be called only in
  // kWritable mode, all other modes will CHECK-fail. The object will have
  // kReadOnly mode after this call on success.
  bool ConvertToReadOnly();
#if BUILDFLAG(IS_APPLE)
  // Same as above, but |mapped_addr| is used as a hint to avoid additional
  // mapping of the memory object.
  // |mapped_addr| must be mapped location of |memory_object_|. If the location
  // is unknown, |mapped_addr| should be |nullptr|.
  bool ConvertToReadOnly(void* mapped_addr);
#endif  // BUILDFLAG(IS_APPLE)

  // Converts the region to unsafe. Returns whether the operation succeeded.
  // Makes the current instance invalid on failure. Can be called only in
  // kWritable mode, all other modes will CHECK-fail. The object will have
  // kUnsafe mode after this call on success.
  bool ConvertToUnsafe();

  // Maps |size| bytes of the shared memory region starting with the given
  // |offset| into the caller's address space using the provided
  // |SharedMemoryMapper|. |offset| must be aligned to value of
  // |SysInfo::VMAllocationGranularity()|. Fails if requested bytes are out of
  // the region limits. Returns the mapping as span on success, or absl::nullopt
  // on failure. The mapped address is guaranteed to have an alignment of at
  // least |kMapMinimumAlignment|.
  absl::optional<span<uint8_t>> MapAt(uint64_t offset,
                                      size_t size,
                                      SharedMemoryMapper* mapper) const;

  // Unmaps the provided shared memory mapping, which must have previously been
  // created by calling |MapAt()| above.
  static void Unmap(span<uint8_t> mapping, SharedMemoryMapper* mapper);

  const UnguessableToken& GetGUID() const { return guid_; }

  size_t GetSize() const { return size_; }

  Mode GetMode() const { return mode_; }

 private:
  FRIEND_TEST_ALL_PREFIXES(PlatformSharedMemoryRegionTest,
                           CreateReadOnlyRegionDeathTest);
  FRIEND_TEST_ALL_PREFIXES(PlatformSharedMemoryRegionTest,
                           CheckPlatformHandlePermissionsCorrespondToMode);
  static PlatformSharedMemoryRegion Create(Mode mode,
                                           size_t size
#if BUILDFLAG(IS_LINUX) || BUILDFLAG(IS_CHROMEOS)
                                           ,
                                           bool executable = false
#endif
  );

  static bool CheckPlatformHandlePermissionsCorrespondToMode(
      PlatformSharedMemoryHandle handle,
      Mode mode,
      size_t size);

  PlatformSharedMemoryRegion(ScopedPlatformSharedMemoryHandle handle,
                             Mode mode,
                             size_t size,
                             const UnguessableToken& guid);

  ScopedPlatformSharedMemoryHandle handle_;
  Mode mode_ = Mode::kReadOnly;
  size_t size_ = 0;
  UnguessableToken guid_;
};

}  // namespace subtle
}  // namespace base

#endif  // BASE_MEMORY_PLATFORM_SHARED_MEMORY_REGION_H_