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// Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
// Licensed under the MIT License:
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
#ifndef CAPNP_ARENA_H_
#define CAPNP_ARENA_H_
#if defined(__GNUC__) && !defined(CAPNP_HEADER_WARNINGS)
#pragma GCC system_header
#endif
#ifndef CAPNP_PRIVATE
#error "This header is only meant to be included by Cap'n Proto's own source code."
#endif
#include <kj/common.h>
#include <kj/mutex.h>
#include <kj/exception.h>
#include <kj/vector.h>
#include <kj/units.h>
#include "common.h"
#include "message.h"
#include "layout.h"
#include <unordered_map>
#if !CAPNP_LITE
#include "capability.h"
#endif // !CAPNP_LITE
namespace capnp {
#if !CAPNP_LITE
class ClientHook;
#endif // !CAPNP_LITE
namespace _ { // private
class SegmentReader;
class SegmentBuilder;
class Arena;
class BuilderArena;
class ReadLimiter;
class Segment;
typedef kj::Id<uint32_t, Segment> SegmentId;
class ReadLimiter {
// Used to keep track of how much data has been processed from a message, and cut off further
// processing if and when a particular limit is reached. This is primarily intended to guard
// against maliciously-crafted messages which contain cycles or overlapping structures. Cycles
// and overlapping are not permitted by the Cap'n Proto format because in many cases they could
// be used to craft a deceptively small message which could consume excessive server resources to
// process, perhaps even sending it into an infinite loop. Actually detecting overlaps would be
// time-consuming, so instead we just keep track of how many words worth of data structures the
// receiver has actually dereferenced and error out if this gets too high.
//
// This counting takes place as you call getters (for non-primitive values) on the message
// readers. If you call the same getter twice, the data it returns may be double-counted. This
// should not be a big deal in most cases -- just set the read limit high enough that it will
// only trigger in unreasonable cases.
//
// This class is "safe" to use from multiple threads for its intended use case. Threads may
// overwrite each others' changes to the counter, but this is OK because it only means that the
// limit is enforced a bit less strictly -- it will still kick in eventually.
public:
inline explicit ReadLimiter(); // No limit.
inline explicit ReadLimiter(WordCount64 limit); // Limit to the given number of words.
inline void reset(WordCount64 limit);
KJ_ALWAYS_INLINE(bool canRead(WordCount64 amount, Arena* arena));
void unread(WordCount64 amount);
// Adds back some words to the limit. Useful when the caller knows they are double-reading
// some data.
private:
volatile uint64_t limit;
// Current limit, decremented each time catRead() is called. Volatile because multiple threads
// could be trying to modify it at once. (This is not real thread-safety, but good enough for
// the purpose of this class. See class comment.)
KJ_DISALLOW_COPY(ReadLimiter);
};
#if !CAPNP_LITE
class BrokenCapFactory {
// Callback for constructing broken caps. We use this so that we can avoid arena.c++ having a
// link-time dependency on capability code that lives in libcapnp-rpc.
public:
virtual kj::Own<ClientHook> newBrokenCap(kj::StringPtr description) = 0;
virtual kj::Own<ClientHook> newNullCap() = 0;
};
#endif // !CAPNP_LITE
class SegmentReader {
public:
inline SegmentReader(Arena* arena, SegmentId id, const word* ptr, SegmentWordCount size,
ReadLimiter* readLimiter);
KJ_ALWAYS_INLINE(bool containsInterval(const void* from, const void* to));
KJ_ALWAYS_INLINE(bool amplifiedRead(WordCount virtualAmount));
// Indicates that the reader should pretend that `virtualAmount` additional data was read even
// though no actual pointer was traversed. This is used e.g. when reading a struct list pointer
// where the element sizes are zero -- the sender could set the list size arbitrarily high and
// cause the receiver to iterate over this list even though the message itself is small, so we
// need to defend against DoS attacks based on this.
inline Arena* getArena();
inline SegmentId getSegmentId();
inline const word* getStartPtr();
inline SegmentWordCount getOffsetTo(const word* ptr);
inline SegmentWordCount getSize();
inline kj::ArrayPtr<const word> getArray();
inline void unread(WordCount64 amount);
// Add back some words to the ReadLimiter.
private:
Arena* arena;
SegmentId id;
kj::ArrayPtr<const word> ptr; // size guaranteed to fit in SEGMENT_WORD_COUNT_BITS bits
ReadLimiter* readLimiter;
KJ_DISALLOW_COPY(SegmentReader);
friend class SegmentBuilder;
};
class SegmentBuilder: public SegmentReader {
public:
inline SegmentBuilder(BuilderArena* arena, SegmentId id, word* ptr, SegmentWordCount size,
ReadLimiter* readLimiter, SegmentWordCount wordsUsed = ZERO * WORDS);
inline SegmentBuilder(BuilderArena* arena, SegmentId id, const word* ptr, SegmentWordCount size,
ReadLimiter* readLimiter);
inline SegmentBuilder(BuilderArena* arena, SegmentId id, decltype(nullptr),
ReadLimiter* readLimiter);
KJ_ALWAYS_INLINE(word* allocate(SegmentWordCount amount));
KJ_ALWAYS_INLINE(void checkWritable());
// Throw an exception if the segment is read-only (meaning it is a reference to external data).
KJ_ALWAYS_INLINE(word* getPtrUnchecked(SegmentWordCount offset));
// Get a writable pointer into the segment. Throws an exception if the segment is read-only (i.e.
// a reference to external immutable data).
inline BuilderArena* getArena();
inline kj::ArrayPtr<const word> currentlyAllocated();
inline void reset();
inline bool isWritable() { return !readOnly; }
inline void tryTruncate(word* from, word* to);
// If `from` points just past the current end of the segment, then move the end back to `to`.
// Otherwise, do nothing.
inline bool tryExtend(word* from, word* to);
// If `from` points just past the current end of the segment, and `to` is within the segment
// boundaries, then move the end up to `to` and return true. Otherwise, do nothing and return
// false.
private:
word* pos;
// Pointer to a pointer to the current end point of the segment, i.e. the location where the
// next object should be allocated.
bool readOnly;
void throwNotWritable();
KJ_DISALLOW_COPY(SegmentBuilder);
};
class Arena {
public:
virtual ~Arena() noexcept(false);
virtual SegmentReader* tryGetSegment(SegmentId id) = 0;
// Gets the segment with the given ID, or return nullptr if no such segment exists.
virtual void reportReadLimitReached() = 0;
// Called to report that the read limit has been reached. See ReadLimiter, below. This invokes
// the VALIDATE_INPUT() macro which may throw an exception; if it returns normally, the caller
// will need to continue with default values.
};
class ReaderArena final: public Arena {
public:
explicit ReaderArena(MessageReader* message);
~ReaderArena() noexcept(false);
KJ_DISALLOW_COPY(ReaderArena);
// implements Arena ------------------------------------------------
SegmentReader* tryGetSegment(SegmentId id) override;
void reportReadLimitReached() override;
private:
MessageReader* message;
ReadLimiter readLimiter;
// Optimize for single-segment messages so that small messages are handled quickly.
SegmentReader segment0;
typedef std::unordered_map<uint, kj::Own<SegmentReader>> SegmentMap;
kj::MutexGuarded<kj::Maybe<kj::Own<SegmentMap>>> moreSegments;
// We need to mutex-guard the segment map because we lazily initialize segments when they are
// first requested, but a Reader is allowed to be used concurrently in multiple threads. Luckily
// this only applies to large messages.
//
// TODO(perf): Thread-local thing instead? Some kind of lockless map? Or do sharing of data
// in a different way, where you have to construct a new MessageReader in each thread (but
// possibly backed by the same data)?
ReaderArena(MessageReader* message, kj::ArrayPtr<const word> firstSegment);
ReaderArena(MessageReader* message, const word* firstSegment, SegmentWordCount firstSegmentSize);
};
class BuilderArena final: public Arena {
// A BuilderArena that does not allow the injection of capabilities.
public:
explicit BuilderArena(MessageBuilder* message);
BuilderArena(MessageBuilder* message, kj::ArrayPtr<MessageBuilder::SegmentInit> segments);
~BuilderArena() noexcept(false);
KJ_DISALLOW_COPY(BuilderArena);
inline SegmentBuilder* getRootSegment() { return &segment0; }
kj::ArrayPtr<const kj::ArrayPtr<const word>> getSegmentsForOutput();
// Get an array of all the segments, suitable for writing out. This only returns the allocated
// portion of each segment, whereas tryGetSegment() returns something that includes
// not-yet-allocated space.
inline CapTableBuilder* getLocalCapTable() {
// Return a CapTableBuilder that merely implements local loopback. That is, you can set
// capabilities, then read the same capabilities back, but there is no intent ever to transmit
// these capabilities. A MessageBuilder that isn't imbued with some other CapTable uses this
// by default.
//
// TODO(cleanup): It's sort of a hack that this exists. In theory, perhaps, unimbued
// MessageBuilders should throw exceptions on any attempt to access capability fields, like
// unimbued MessageReaders do. However, lots of code exists which uses MallocMessageBuilder
// as a temporary holder for data to be copied in and out (without being serialized), and it
// is expected that such data can include capabilities, which is admittedly reasonable.
// Therefore, all MessageBuilders must have a cap table by default. Arguably we should
// deprecate this usage and instead define a new helper type for this exact purpose.
return &localCapTable;
}
SegmentBuilder* getSegment(SegmentId id);
// Get the segment with the given id. Crashes or throws an exception if no such segment exists.
struct AllocateResult {
SegmentBuilder* segment;
word* words;
};
AllocateResult allocate(SegmentWordCount amount);
// Find a segment with at least the given amount of space available and allocate the space.
// Note that allocating directly from a particular segment is much faster, but allocating from
// the arena is guaranteed to succeed. Therefore callers should try to allocate from a specific
// segment first if there is one, then fall back to the arena.
SegmentBuilder* addExternalSegment(kj::ArrayPtr<const word> content);
// Add a new segment to the arena which points to some existing memory region. The segment is
// assumed to be completley full; the arena will never allocate from it. In fact, the segment
// is considered read-only. Any attempt to get a Builder pointing into this segment will throw
// an exception. Readers are allowed, however.
//
// This can be used to inject some external data into a message without a copy, e.g. embedding a
// large mmap'd file into a message as `Data` without forcing that data to actually be read in
// from disk (until the message itself is written out). `Orphanage` provides the public API for
// this feature.
// implements Arena ------------------------------------------------
SegmentReader* tryGetSegment(SegmentId id) override;
void reportReadLimitReached() override;
private:
MessageBuilder* message;
ReadLimiter dummyLimiter;
class LocalCapTable: public CapTableBuilder {
#if !CAPNP_LITE
public:
kj::Maybe<kj::Own<ClientHook>> extractCap(uint index) override;
uint injectCap(kj::Own<ClientHook>&& cap) override;
void dropCap(uint index) override;
private:
kj::Vector<kj::Maybe<kj::Own<ClientHook>>> capTable;
#endif // ! CAPNP_LITE
};
LocalCapTable localCapTable;
SegmentBuilder segment0;
kj::ArrayPtr<const word> segment0ForOutput;
struct MultiSegmentState {
kj::Vector<kj::Own<SegmentBuilder>> builders;
kj::Vector<kj::ArrayPtr<const word>> forOutput;
};
kj::Maybe<kj::Own<MultiSegmentState>> moreSegments;
SegmentBuilder* segmentWithSpace = nullptr;
// When allocating, look for space in this segment first before resorting to allocating a new
// segment. This is not necessarily the last segment because addExternalSegment() may add a
// segment that is already-full, in which case we don't update this pointer.
template <typename T> // Can be `word` or `const word`.
SegmentBuilder* addSegmentInternal(kj::ArrayPtr<T> content);
};
// =======================================================================================
inline ReadLimiter::ReadLimiter()
: limit(kj::maxValue) {}
inline ReadLimiter::ReadLimiter(WordCount64 limit): limit(unbound(limit / WORDS)) {}
inline void ReadLimiter::reset(WordCount64 limit) { this->limit = unbound(limit / WORDS); }
inline bool ReadLimiter::canRead(WordCount64 amount, Arena* arena) {
// Be careful not to store an underflowed value into `limit`, even if multiple threads are
// decrementing it.
uint64_t current = limit;
if (KJ_UNLIKELY(unbound(amount / WORDS) > current)) {
arena->reportReadLimitReached();
return false;
} else {
limit = current - unbound(amount / WORDS);
return true;
}
}
// -------------------------------------------------------------------
inline SegmentReader::SegmentReader(Arena* arena, SegmentId id, const word* ptr,
SegmentWordCount size, ReadLimiter* readLimiter)
: arena(arena), id(id), ptr(kj::arrayPtr(ptr, unbound(size / WORDS))),
readLimiter(readLimiter) {}
inline bool SegmentReader::containsInterval(const void* from, const void* to) {
return from >= this->ptr.begin() && to <= this->ptr.end() && from <= to &&
readLimiter->canRead(
intervalLength(reinterpret_cast<const byte*>(from),
reinterpret_cast<const byte*>(to),
MAX_SEGMENT_WORDS * BYTES_PER_WORD)
/ BYTES_PER_WORD,
arena);
}
inline bool SegmentReader::amplifiedRead(WordCount virtualAmount) {
return readLimiter->canRead(virtualAmount, arena);
}
inline Arena* SegmentReader::getArena() { return arena; }
inline SegmentId SegmentReader::getSegmentId() { return id; }
inline const word* SegmentReader::getStartPtr() { return ptr.begin(); }
inline SegmentWordCount SegmentReader::getOffsetTo(const word* ptr) {
KJ_IREQUIRE(this->ptr.begin() <= ptr && ptr <= this->ptr.end());
return intervalLength(this->ptr.begin(), ptr, MAX_SEGMENT_WORDS);
}
inline SegmentWordCount SegmentReader::getSize() {
return assumeBits<SEGMENT_WORD_COUNT_BITS>(ptr.size()) * WORDS;
}
inline kj::ArrayPtr<const word> SegmentReader::getArray() { return ptr; }
inline void SegmentReader::unread(WordCount64 amount) { readLimiter->unread(amount); }
// -------------------------------------------------------------------
inline SegmentBuilder::SegmentBuilder(
BuilderArena* arena, SegmentId id, word* ptr, SegmentWordCount size,
ReadLimiter* readLimiter, SegmentWordCount wordsUsed)
: SegmentReader(arena, id, ptr, size, readLimiter),
pos(ptr + wordsUsed), readOnly(false) {}
inline SegmentBuilder::SegmentBuilder(
BuilderArena* arena, SegmentId id, const word* ptr, SegmentWordCount size,
ReadLimiter* readLimiter)
: SegmentReader(arena, id, ptr, size, readLimiter),
// const_cast is safe here because the member won't ever be dereferenced because it appears
// to point to the end of the segment anyway.
pos(const_cast<word*>(ptr + size)), readOnly(true) {}
inline SegmentBuilder::SegmentBuilder(BuilderArena* arena, SegmentId id, decltype(nullptr),
ReadLimiter* readLimiter)
: SegmentReader(arena, id, nullptr, ZERO * WORDS, readLimiter),
pos(nullptr), readOnly(false) {}
inline word* SegmentBuilder::allocate(SegmentWordCount amount) {
if (intervalLength(pos, ptr.end(), MAX_SEGMENT_WORDS) < amount) {
// Not enough space in the segment for this allocation.
return nullptr;
} else {
// Success.
word* result = pos;
pos = pos + amount;
return result;
}
}
inline void SegmentBuilder::checkWritable() {
if (KJ_UNLIKELY(readOnly)) throwNotWritable();
}
inline word* SegmentBuilder::getPtrUnchecked(SegmentWordCount offset) {
return const_cast<word*>(ptr.begin() + offset);
}
inline BuilderArena* SegmentBuilder::getArena() {
// Down-cast safe because SegmentBuilder's constructor always initializes its SegmentReader base
// class with an Arena pointer that actually points to a BuilderArena.
return static_cast<BuilderArena*>(arena);
}
inline kj::ArrayPtr<const word> SegmentBuilder::currentlyAllocated() {
return kj::arrayPtr(ptr.begin(), pos - ptr.begin());
}
inline void SegmentBuilder::reset() {
word* start = getPtrUnchecked(ZERO * WORDS);
memset(start, 0, (pos - start) * sizeof(word));
pos = start;
}
inline void SegmentBuilder::tryTruncate(word* from, word* to) {
if (pos == from) pos = to;
}
inline bool SegmentBuilder::tryExtend(word* from, word* to) {
// Careful about overflow.
if (pos == from && to <= ptr.end() && to >= from) {
pos = to;
return true;
} else {
return false;
}
}
} // namespace _ (private)
} // namespace capnp
#endif // CAPNP_ARENA_H_