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/*
* Copyright (C) 2018 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "src/tracing/core/packet_stream_validator.h"
#include <stddef.h>
#include <cinttypes>
#include "perfetto/base/logging.h"
#include "perfetto/ext/base/utils.h"
#include "perfetto/protozero/proto_utils.h"
#include "protos/perfetto/trace/trace_packet.pbzero.h"
namespace perfetto {
namespace {
using protozero::proto_utils::ProtoWireType;
const uint32_t kReservedFieldIds[] = {
protos::pbzero::TracePacket::kTrustedUidFieldNumber,
protos::pbzero::TracePacket::kTrustedPacketSequenceIdFieldNumber,
protos::pbzero::TracePacket::kTraceConfigFieldNumber,
protos::pbzero::TracePacket::kTraceStatsFieldNumber,
protos::pbzero::TracePacket::kCompressedPacketsFieldNumber,
protos::pbzero::TracePacket::kSynchronizationMarkerFieldNumber,
protos::pbzero::TracePacket::kTrustedPidFieldNumber,
};
// This translation unit is quite subtle and perf-sensitive. Remember to check
// BM_PacketStreamValidator in perfetto_benchmarks when making changes.
// Checks that a packet, spread over several slices, is well-formed and doesn't
// contain reserved top-level fields.
// The checking logic is based on a state-machine that skips the fields' payload
// and operates as follows:
// +-------------------------------+ <-------------------------+
// +----------> | Read field preamble (varint) | <----------------------+ |
// | +-------------------------------+ | |
// | | | | | |
// | <Varint> <Fixed 32/64> <Length-delimited field> | |
// | V | V | |
// | +------------------+ | +--------------+ | |
// | | Read field value | | | Read length | | |
// | | (another varint) | | | (varint) | | |
// | +------------------+ | +--------------+ | |
// | | V V | |
// +-----------+ +----------------+ +-----------------+ | |
// | Skip 4/8 Bytes | | Skip $len Bytes |-------+ |
// +----------------+ +-----------------+ |
// | |
// +------------------------------------------+
class ProtoFieldParserFSM {
public:
// This method effectively continuously parses varints (either for the field
// preamble or the payload or the submessage length) and tells the caller
// (the Validate() method) how many bytes to skip until the next field.
size_t Push(uint8_t octet) {
varint_ |= static_cast<uint64_t>(octet & 0x7F) << varint_shift_;
if (octet & 0x80) {
varint_shift_ += 7;
if (varint_shift_ >= 64) {
// Do not invoke UB on next call.
varint_shift_ = 0;
state_ = kInvalidVarInt;
}
return 0;
}
uint64_t varint = varint_;
varint_ = 0;
varint_shift_ = 0;
switch (state_) {
case kFieldPreamble: {
uint64_t field_type = varint & 7; // 7 = 0..0111
auto field_id = static_cast<uint32_t>(varint >> 3);
// Check if the field id is reserved, go into an error state if it is.
for (size_t i = 0; i < base::ArraySize(kReservedFieldIds); ++i) {
if (field_id == kReservedFieldIds[i]) {
state_ = kWroteReservedField;
return 0;
}
}
// The field type is legit, now check it's well formed and within
// boundaries.
if (field_type == static_cast<uint64_t>(ProtoWireType::kVarInt)) {
state_ = kVarIntValue;
} else if (field_type ==
static_cast<uint64_t>(ProtoWireType::kFixed32)) {
return 4;
} else if (field_type ==
static_cast<uint64_t>(ProtoWireType::kFixed64)) {
return 8;
} else if (field_type ==
static_cast<uint64_t>(ProtoWireType::kLengthDelimited)) {
state_ = kLenDelimitedLen;
} else {
state_ = kUnknownFieldType;
}
return 0;
}
case kVarIntValue: {
// Consume the int field payload and go back to the next field.
state_ = kFieldPreamble;
return 0;
}
case kLenDelimitedLen: {
if (varint > protozero::proto_utils::kMaxMessageLength) {
state_ = kMessageTooBig;
return 0;
}
state_ = kFieldPreamble;
return static_cast<size_t>(varint);
}
case kWroteReservedField:
case kUnknownFieldType:
case kMessageTooBig:
case kInvalidVarInt:
// Persistent error states.
return 0;
} // switch(state_)
return 0; // To keep GCC happy.
}
// Queried at the end of the all payload. A message is well-formed only
// if the FSM is back to the state where it should parse the next field and
// hasn't started parsing any preamble.
bool valid() const { return state_ == kFieldPreamble && varint_shift_ == 0; }
int state() const { return static_cast<int>(state_); }
private:
enum State {
kFieldPreamble = 0, // Parsing the varint for the field preamble.
kVarIntValue, // Parsing the varint value for the field payload.
kLenDelimitedLen, // Parsing the length of the length-delimited field.
// Error states:
kWroteReservedField, // Tried to set a reserved field id.
kUnknownFieldType, // Encountered an invalid field type.
kMessageTooBig, // Size of the length delimited message was too big.
kInvalidVarInt, // VarInt larger than 64 bits.
};
State state_ = kFieldPreamble;
uint64_t varint_ = 0;
uint32_t varint_shift_ = 0;
};
} // namespace
// static
bool PacketStreamValidator::Validate(const Slices& slices) {
ProtoFieldParserFSM parser;
size_t skip_bytes = 0;
for (const Slice& slice : slices) {
for (size_t i = 0; i < slice.size;) {
const size_t skip_bytes_cur_slice = std::min(skip_bytes, slice.size - i);
if (skip_bytes_cur_slice > 0) {
i += skip_bytes_cur_slice;
skip_bytes -= skip_bytes_cur_slice;
} else {
uint8_t octet = *(reinterpret_cast<const uint8_t*>(slice.start) + i);
skip_bytes = parser.Push(octet);
i++;
}
}
}
if (skip_bytes == 0 && parser.valid())
return true;
PERFETTO_DLOG("Packet validation error (state %d, skip = %zu)",
parser.state(), skip_bytes);
return false;
}
} // namespace perfetto
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