common.h

//===-- common.h ------------------------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// This file contains code that is common between the crash handler and the
// GuardedPoolAllocator.

#ifndef GWP_ASAN_COMMON_H_
#define GWP_ASAN_COMMON_H_

#include "gwp_asan/definitions.h"
#include "gwp_asan/options.h"

#include <stddef.h>
#include <stdint.h>

namespace gwp_asan {
enum class Error {
  UNKNOWN,
  USE_AFTER_FREE,
  DOUBLE_FREE,
  INVALID_FREE,
  BUFFER_OVERFLOW,
  BUFFER_UNDERFLOW
};

const char *ErrorToString(const Error &E);

static constexpr uint64_t kInvalidThreadID = UINT64_MAX;
// Get the current thread ID, or kInvalidThreadID if failure. Note: This
// implementation is platform-specific.
uint64_t getThreadID();

// This struct contains all the metadata recorded about a single allocation made
// by GWP-ASan. If `AllocationMetadata.Addr` is zero, the metadata is non-valid.
struct AllocationMetadata {
  // The number of bytes used to store a compressed stack frame. On 64-bit
  // platforms, assuming a compression ratio of 50%, this should allow us to
  // store ~64 frames per trace.
  static constexpr size_t kStackFrameStorageBytes = 256;

  // Maximum number of stack frames to collect on allocation/deallocation. The
  // actual number of collected frames may be less than this as the stack
  // frames are compressed into a fixed memory range.
  static constexpr size_t kMaxTraceLengthToCollect = 128;

  // Records the given allocation metadata into this struct.
  void RecordAllocation(uintptr_t Addr, size_t Size);
  // Record that this allocation is now deallocated.
  void RecordDeallocation();

  struct CallSiteInfo {
    // Record the current backtrace to this callsite.
    void RecordBacktrace(options::Backtrace_t Backtrace);

    // The compressed backtrace to the allocation/deallocation.
    uint8_t CompressedTrace[kStackFrameStorageBytes];
    // The thread ID for this trace, or kInvalidThreadID if not available.
    uint64_t ThreadID = kInvalidThreadID;
    // The size of the compressed trace (in bytes). Zero indicates that no
    // trace was collected.
    size_t TraceSize = 0;
  };

  // The address of this allocation. If zero, the rest of this struct isn't
  // valid, as the allocation has never occurred.
  uintptr_t Addr = 0;
  // Represents the actual size of the allocation.
  size_t Size = 0;

  CallSiteInfo AllocationTrace;
  CallSiteInfo DeallocationTrace;

  // Whether this allocation has been deallocated yet.
  bool IsDeallocated = false;
};

// This holds the state that's shared between the GWP-ASan allocator and the
// crash handler. This, in conjunction with the Metadata array, forms the entire
// set of information required for understanding a GWP-ASan crash.
struct AllocatorState {
  // Returns whether the provided pointer is a current sampled allocation that
  // is owned by this pool.
  GWP_ASAN_ALWAYS_INLINE bool pointerIsMine(const void *Ptr) const {
    uintptr_t P = reinterpret_cast<uintptr_t>(Ptr);
    return P < GuardedPagePoolEnd && GuardedPagePool <= P;
  }

  // Returns the address of the N-th guarded slot.
  uintptr_t slotToAddr(size_t N) const;

  // Returns the largest allocation that is supported by this pool.
  size_t maximumAllocationSize() const;

  // Gets the nearest slot to the provided address.
  size_t getNearestSlot(uintptr_t Ptr) const;

  // Returns whether the provided pointer is a guard page or not. The pointer
  // must be within memory owned by this pool, else the result is undefined.
  bool isGuardPage(uintptr_t Ptr) const;

  // The number of guarded slots that this pool holds.
  size_t MaxSimultaneousAllocations = 0;

  // Pointer to the pool of guarded slots. Note that this points to the start of
  // the pool (which is a guard page), not a pointer to the first guarded page.
  uintptr_t GuardedPagePool = 0;
  uintptr_t GuardedPagePoolEnd = 0;

  // Cached page size for this system in bytes.
  size_t PageSize = 0;

  // The type and address of an internally-detected failure. For INVALID_FREE
  // and DOUBLE_FREE, these errors are detected in GWP-ASan, which will set
  // these values and terminate the process.
  Error FailureType = Error::UNKNOWN;
  uintptr_t FailureAddress = 0;
};

} // namespace gwp_asan
#endif // GWP_ASAN_COMMON_H_