// Copyright (c) 2015 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_
#define BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_
#include <stdint.h>
#include <atomic>
#include <memory>
#include "base/atomicops.h"
#include "base/base_export.h"
#include "base/files/file_path.h"
#include "base/gtest_prod_util.h"
#include "base/macros.h"
#include "base/strings/string_piece.h"
namespace base {
class HistogramBase;
class MemoryMappedFile;
class SharedMemory;
// Simple allocator for pieces of a memory block that may be persistent
// to some storage or shared across multiple processes. This class resides
// under base/metrics because it was written for that purpose. It is,
// however, fully general-purpose and can be freely moved to base/memory
// if other uses are found.
//
// This class provides for thread-secure (i.e. safe against other threads
// or processes that may be compromised and thus have malicious intent)
// allocation of memory within a designated block and also a mechanism by
// which other threads can learn of these allocations.
//
// There is (currently) no way to release an allocated block of data because
// doing so would risk invalidating pointers held by other processes and
// greatly complicate the allocation algorithm.
//
// Construction of this object can accept new, clean (i.e. zeroed) memory
// or previously initialized memory. In the first case, construction must
// be allowed to complete before letting other allocators attach to the same
// segment. In other words, don't share the segment until at least one
// allocator has been attached to it.
//
// Note that memory not in active use is not accessed so it is possible to
// use virtual memory, including memory-mapped files, as backing storage with
// the OS "pinning" new (zeroed) physical RAM pages only as they are needed.
class BASE_EXPORT PersistentMemoryAllocator {
public:
typedef uint32_t Reference;
// Iterator for going through all iterable memory records in an allocator.
// Like the allocator itself, iterators are lock-free and thread-secure.
// That means that multiple threads can share an iterator and the same
// reference will not be returned twice.
//
// Iteration, in general, is tolerant of corrupted memory. It will return
// what it can and stop only when corruption forces it to. Bad corruption
// could cause the same object to be returned many times but it will
// eventually quit.
class BASE_EXPORT Iterator {
public:
// Constructs an iterator on a given |allocator|, starting at the beginning.
// The allocator must live beyond the lifetime of the iterator. This class
// has read-only access to the allocator (hence "const") but the returned
// references can be used on a read/write version, too.
explicit Iterator(const PersistentMemoryAllocator* allocator);
// As above but resuming from the |starting_after| reference. The first call
// to GetNext() will return the next object found after that reference. The
// reference must be to an "iterable" object; references to non-iterable
// objects (those that never had MakeIterable() called for them) will cause
// a run-time error.
Iterator(const PersistentMemoryAllocator* allocator,
Reference starting_after);
// Gets the next iterable, storing that type in |type_return|. The actual
// return value is a reference to the allocation inside the allocator or
// zero if there are no more. GetNext() may still be called again at a
// later time to retrieve any new allocations that have been added.
Reference GetNext(uint32_t* type_return);
// Similar to above but gets the next iterable of a specific |type_match|.
// This should not be mixed with calls to GetNext() because any allocations
// skipped here due to a type mis-match will never be returned by later
// calls to GetNext() meaning it's possible to completely miss entries.
Reference GetNextOfType(uint32_t type_match);
// Converts references to objects. This is a convenience method so that
// users of the iterator don't need to also have their own pointer to the
// allocator over which the iterator runs in order to retrieve objects.
// Because the iterator is not read/write, only "const" objects can be
// fetched. Non-const objects can be fetched using the reference on a
// non-const (external) pointer to the same allocator (or use const_cast
// to remove the qualifier).
template <typename T>
const T* GetAsObject(Reference ref, uint32_t type_id) const {
return allocator_->GetAsObject<T>(ref, type_id);
}
private:
// Weak-pointer to memory allocator being iterated over.
const PersistentMemoryAllocator* allocator_;
// The last record that was returned.
std::atomic<Reference> last_record_;
// The number of records found; used for detecting loops.
std::atomic<uint32_t> record_count_;
DISALLOW_COPY_AND_ASSIGN(Iterator);
};
// Returned information about the internal state of the heap.
struct MemoryInfo {
size_t total;
size_t free;
};
enum : Reference {
kReferenceNull = 0 // A common "null" reference value.
};
enum : uint32_t {
kTypeIdAny = 0 // Match any type-id inside GetAsObject().
};
// This is the standard file extension (suitable for being passed to the
// AddExtension() method of base::FilePath) for dumps of persistent memory.
static const base::FilePath::CharType kFileExtension[];
// The allocator operates on any arbitrary block of memory. Creation and
// persisting or sharing of that block with another process is the
// responsibility of the caller. The allocator needs to know only the
// block's |base| address, the total |size| of the block, and any internal
// |page| size (zero if not paged) across which allocations should not span.
// The |id| is an arbitrary value the caller can use to identify a
// particular memory segment. It will only be loaded during the initial
// creation of the segment and can be checked by the caller for consistency.
// The |name|, if provided, is used to distinguish histograms for this
// allocator. Only the primary owner of the segment should define this value;
// other processes can learn it from the shared state. If the underlying
// memory is |readonly| then no changes will be made to it. The resulting
// object should be stored as a "const" pointer.
//
// PersistentMemoryAllocator does NOT take ownership of the memory block.
// The caller must manage it and ensure it stays available throughout the
// lifetime of this object.
//
// Memory segments for sharing must have had an allocator attached to them
// before actually being shared. If the memory segment was just created, it
// should be zeroed before being passed here. If it was an existing segment,
// the values here will be compared to copies stored in the shared segment
// as a guard against corruption.
//
// Make sure that the memory segment is acceptable (see IsMemoryAcceptable()
// method below) before construction if the definition of the segment can
// vary in any way at run-time. Invalid memory segments will cause a crash.
PersistentMemoryAllocator(void* base, size_t size, size_t page_size,
uint64_t id, base::StringPiece name,
bool readonly);
virtual ~PersistentMemoryAllocator();
// Check if memory segment is acceptable for creation of an Allocator. This
// doesn't do any analysis of the data and so doesn't guarantee that the
// contents are valid, just that the paramaters won't cause the program to
// abort. The IsCorrupt() method will report detection of data problems
// found during construction and general operation.
static bool IsMemoryAcceptable(const void* data, size_t size,
size_t page_size, bool readonly);
// Get the internal identifier for this persistent memory segment.
uint64_t Id() const;
// Get the internal name of this allocator (possibly an empty string).
const char* Name() const;
// Is this segment open only for read?
bool IsReadonly() { return readonly_; }
// Create internal histograms for tracking memory use and allocation sizes
// for allocator of |name| (which can simply be the result of Name()). This
// is done seperately from construction for situations such as when the
// histograms will be backed by memory provided by this very allocator.
//
// IMPORTANT: Callers must update tools/metrics/histograms/histograms.xml
// with the following histograms:
// UMA.PersistentAllocator.name.Allocs
// UMA.PersistentAllocator.name.UsedPct
void CreateTrackingHistograms(base::StringPiece name);
// Direct access to underlying memory segment. If the segment is shared
// across threads or processes, reading data through these values does
// not guarantee consistency. Use with care. Do not write.
const void* data() const { return const_cast<const char*>(mem_base_); }
size_t length() const { return mem_size_; }
size_t size() const { return mem_size_; }
size_t used() const;
// Get an object referenced by a |ref|. For safety reasons, the |type_id|
// code and size-of(|T|) are compared to ensure the reference is valid
// and cannot return an object outside of the memory segment. A |type_id| of
// kTypeIdAny (zero) will match any though the size is still checked. NULL is
// returned if any problem is detected, such as corrupted storage or incorrect
// parameters. Callers MUST check that the returned value is not-null EVERY
// TIME before accessing it or risk crashing! Once dereferenced, the pointer
// is safe to reuse forever.
//
// NOTE: Though this method will guarantee that an object of the specified
// type can be accessed without going outside the bounds of the memory
// segment, it makes no guarantees of the validity of the data within the
// object itself. If it is expected that the contents of the segment could
// be compromised with malicious intent, the object must be hardened as well.
//
// Though the persistent data may be "volatile" if it is shared with
// other processes, such is not necessarily the case. The internal
// "volatile" designation is discarded so as to not propagate the viral
// nature of that keyword to the caller. It can add it back, if necessary,
// based on knowledge of how the allocator is being used.
template <typename T>
T* GetAsObject(Reference ref, uint32_t type_id) {
static_assert(!std::is_polymorphic<T>::value, "no polymorphic objects");
return const_cast<T*>(
reinterpret_cast<volatile T*>(GetBlockData(ref, type_id, sizeof(T))));
}
template <typename T>
const T* GetAsObject(Reference ref, uint32_t type_id) const {
static_assert(!std::is_polymorphic<T>::value, "no polymorphic objects");
return const_cast<const T*>(
reinterpret_cast<const volatile T*>(GetBlockData(
ref, type_id, sizeof(T))));
}
// Get the number of bytes allocated to a block. This is useful when storing
// arrays in order to validate the ending boundary. The returned value will
// include any padding added to achieve the required alignment and so could
// be larger than given in the original Allocate() request.
size_t GetAllocSize(Reference ref) const;
// Access the internal "type" of an object. This generally isn't necessary
// but can be used to "clear" the type and so effectively mark it as deleted
// even though the memory stays valid and allocated. Changing the type is
// an atomic compare/exchange and so requires knowing the existing value.
// It will return false if the existing type is not what is expected.
uint32_t GetType(Reference ref) const;
bool ChangeType(Reference ref, uint32_t to_type_id, uint32_t from_type_id);
// Reserve space in the memory segment of the desired |size| and |type_id|.
// A return value of zero indicates the allocation failed, otherwise the
// returned reference can be used by any process to get a real pointer via
// the GetAsObject() call.
Reference Allocate(size_t size, uint32_t type_id);
// Allocated objects can be added to an internal list that can then be
// iterated over by other processes. If an allocated object can be found
// another way, such as by having its reference within a different object
// that will be made iterable, then this call is not necessary. This always
// succeeds unless corruption is detected; check IsCorrupted() to find out.
// Once an object is made iterable, its position in iteration can never
// change; new iterable objects will always be added after it in the series.
void MakeIterable(Reference ref);
// Get the information about the amount of free space in the allocator. The
// amount of free space should be treated as approximate due to extras from
// alignment and metadata. Concurrent allocations from other threads will
// also make the true amount less than what is reported.
void GetMemoryInfo(MemoryInfo* meminfo) const;
// If there is some indication that the memory has become corrupted,
// calling this will attempt to prevent further damage by indicating to
// all processes that something is not as expected.
void SetCorrupt() const;
// This can be called to determine if corruption has been detected in the
// segment, possibly my a malicious actor. Once detected, future allocations
// will fail and iteration may not locate all objects.
bool IsCorrupt() const;
// Flag set if an allocation has failed because the memory segment was full.
bool IsFull() const;
// Update those "tracking" histograms which do not get updates during regular
// operation, such as how much memory is currently used. This should be
// called before such information is to be displayed or uploaded.
void UpdateTrackingHistograms();
protected:
volatile char* const mem_base_; // Memory base. (char so sizeof guaranteed 1)
const uint32_t mem_size_; // Size of entire memory segment.
const uint32_t mem_page_; // Page size allocations shouldn't cross.
private:
struct SharedMetadata;
struct BlockHeader;
static const uint32_t kAllocAlignment;
static const Reference kReferenceQueue;
// The shared metadata is always located at the top of the memory segment.
// These convenience functions eliminate constant casting of the base
// pointer within the code.
const SharedMetadata* shared_meta() const {
return reinterpret_cast<const SharedMetadata*>(
const_cast<const char*>(mem_base_));
}
SharedMetadata* shared_meta() {
return reinterpret_cast<SharedMetadata*>(const_cast<char*>(mem_base_));
}
// Actual method for doing the allocation.
Reference AllocateImpl(size_t size, uint32_t type_id);
// Get the block header associated with a specific reference.
const volatile BlockHeader* GetBlock(Reference ref, uint32_t type_id,
uint32_t size, bool queue_ok,
bool free_ok) const;
volatile BlockHeader* GetBlock(Reference ref, uint32_t type_id, uint32_t size,
bool queue_ok, bool free_ok) {
return const_cast<volatile BlockHeader*>(
const_cast<const PersistentMemoryAllocator*>(this)->GetBlock(
ref, type_id, size, queue_ok, free_ok));
}
// Get the actual data within a block associated with a specific reference.
const volatile void* GetBlockData(Reference ref, uint32_t type_id,
uint32_t size) const;
volatile void* GetBlockData(Reference ref, uint32_t type_id,
uint32_t size) {
return const_cast<volatile void*>(
const_cast<const PersistentMemoryAllocator*>(this)->GetBlockData(
ref, type_id, size));
}
const bool readonly_; // Indicates access to read-only memory.
std::atomic<bool> corrupt_; // Local version of "corrupted" flag.
HistogramBase* allocs_histogram_; // Histogram recording allocs.
HistogramBase* used_histogram_; // Histogram recording used space.
friend class PersistentMemoryAllocatorTest;
FRIEND_TEST_ALL_PREFIXES(PersistentMemoryAllocatorTest, AllocateAndIterate);
DISALLOW_COPY_AND_ASSIGN(PersistentMemoryAllocator);
};
// This allocator uses a local memory block it allocates from the general
// heap. It is generally used when some kind of "death rattle" handler will
// save the contents to persistent storage during process shutdown. It is
// also useful for testing.
class BASE_EXPORT LocalPersistentMemoryAllocator
: public PersistentMemoryAllocator {
public:
LocalPersistentMemoryAllocator(size_t size, uint64_t id,
base::StringPiece name);
~LocalPersistentMemoryAllocator() override;
private:
// Allocates a block of local memory of the specified |size|, ensuring that
// the memory will not be physically allocated until accessed and will read
// as zero when that happens.
static void* AllocateLocalMemory(size_t size);
// Deallocates a block of local |memory| of the specified |size|.
static void DeallocateLocalMemory(void* memory, size_t size);
DISALLOW_COPY_AND_ASSIGN(LocalPersistentMemoryAllocator);
};
// This allocator takes a shared-memory object and performs allocation from
// it. The memory must be previously mapped via Map() or MapAt(). The allocator
// takes ownership of the memory object.
class BASE_EXPORT SharedPersistentMemoryAllocator
: public PersistentMemoryAllocator {
public:
SharedPersistentMemoryAllocator(std::unique_ptr<SharedMemory> memory,
uint64_t id,
base::StringPiece name,
bool read_only);
~SharedPersistentMemoryAllocator() override;
SharedMemory* shared_memory() { return shared_memory_.get(); }
// Ensure that the memory isn't so invalid that it won't crash when passing it
// to the allocator. This doesn't guarantee the data is valid, just that it
// won't cause the program to abort. The existing IsCorrupt() call will handle
// the rest.
static bool IsSharedMemoryAcceptable(const SharedMemory& memory);
private:
std::unique_ptr<SharedMemory> shared_memory_;
DISALLOW_COPY_AND_ASSIGN(SharedPersistentMemoryAllocator);
};
#if !defined(OS_NACL) // NACL doesn't support any kind of file access in build.
// This allocator takes a memory-mapped file object and performs allocation
// from it. The allocator takes ownership of the file object.
class BASE_EXPORT FilePersistentMemoryAllocator
: public PersistentMemoryAllocator {
public:
// A |max_size| of zero will use the length of the file as the maximum
// size. The |file| object must have been already created with sufficient
// permissions (read, read/write, or read/write/extend).
FilePersistentMemoryAllocator(std::unique_ptr<MemoryMappedFile> file,
size_t max_size,
uint64_t id,
base::StringPiece name,
bool read_only);
~FilePersistentMemoryAllocator() override;
// Ensure that the file isn't so invalid that it won't crash when passing it
// to the allocator. This doesn't guarantee the file is valid, just that it
// won't cause the program to abort. The existing IsCorrupt() call will handle
// the rest.
static bool IsFileAcceptable(const MemoryMappedFile& file, bool read_only);
private:
std::unique_ptr<MemoryMappedFile> mapped_file_;
DISALLOW_COPY_AND_ASSIGN(FilePersistentMemoryAllocator);
};
#endif // !defined(OS_NACL)
} // namespace base
#endif // BASE_METRICS_PERSISTENT_MEMORY_ALLOCATOR_H_