Update from chromium 62675d9fb31fb8cedc40f68e78e8445a74f362e7

sandbox/linux/seccomp-bpf/trap.h

+// Copyright (c) 2012 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 SANDBOX_LINUX_SECCOMP_BPF_TRAP_H__
+#define SANDBOX_LINUX_SECCOMP_BPF_TRAP_H__
+
+#include <signal.h>
+#include <stdint.h>
+
+#include <map>
+
+#include "base/macros.h"
+#include "sandbox/linux/bpf_dsl/trap_registry.h"
+#include "sandbox/sandbox_export.h"
+
+namespace sandbox {
+
+// The Trap class allows a BPF filter program to branch out to user space by
+// raising a SIGSYS signal.
+// N.B.: This class does not perform any synchronization operations. If
+//   modifications are made to any of the traps, it is the caller's
+//   responsibility to ensure that this happens in a thread-safe fashion.
+//   Preferably, that means that no other threads should be running at that
+//   time. For the purposes of our sandbox, this assertion should always be
+//   true. Threads are incompatible with the seccomp sandbox anyway.
+class SANDBOX_EXPORT Trap : public bpf_dsl::TrapRegistry {
+ public:
+  virtual uint16_t Add(TrapFnc fnc, const void* aux, bool safe) override;
+
+  virtual bool EnableUnsafeTraps() override;
+
+  // Registry returns the trap registry used by Trap's SIGSYS handler,
+  // creating it if necessary.
+  static bpf_dsl::TrapRegistry* Registry();
+
+  // Registers a new trap handler and sets up the appropriate SIGSYS handler
+  // as needed.
+  // N.B.: This makes a permanent state change. Traps cannot be unregistered,
+  //   as that would break existing BPF filters that are still active.
+  // TODO(mdempsky): Deprecated; remove.
+  static uint16_t MakeTrap(TrapFnc fnc, const void* aux, bool safe);
+
+  // Enables support for unsafe traps in the SIGSYS signal handler. This is a
+  // one-way fuse. It works in conjunction with the BPF compiler emitting code
+  // that unconditionally allows system calls, if they have a magic return
+  // address (i.e. SandboxSyscall(-1)).
+  // Once unsafe traps are enabled, the sandbox is essentially compromised.
+  // But this is still a very useful feature for debugging purposes. Use with
+  // care. This feature is availably only if enabled by the user (see above).
+  // Returns "true", if unsafe traps were turned on.
+  // TODO(mdempsky): Deprecated; remove.
+  static bool EnableUnsafeTrapsInSigSysHandler();
+
+ private:
+  struct TrapKey {
+    TrapKey() : fnc(NULL), aux(NULL), safe(false) {}
+    TrapKey(TrapFnc f, const void* a, bool s) : fnc(f), aux(a), safe(s) {}
+    TrapFnc fnc;
+    const void* aux;
+    bool safe;
+    bool operator<(const TrapKey&) const;
+  };
+  typedef std::map<TrapKey, uint16_t> TrapIds;
+
+  // Our constructor is private. A shared global instance is created
+  // automatically as needed.
+  Trap();
+
+  // The destructor is unimplemented. Don't ever attempt to destruct this
+  // object. It'll break subsequent system calls that trigger a SIGSYS.
+  ~Trap();
+
+  static void SigSysAction(int nr, siginfo_t* info, void* void_context);
+
+  // Make sure that SigSys is not inlined in order to get slightly better crash
+  // dumps.
+  void SigSys(int nr, siginfo_t* info, void* void_context)
+      __attribute__((noinline));
+  bool SandboxDebuggingAllowedByUser() const;
+
+  // We have a global singleton that handles all of our SIGSYS traps. This
+  // variable must never be deallocated after it has been set up initially, as
+  // there is no way to reset in-kernel BPF filters that generate SIGSYS
+  // events.
+  static Trap* global_trap_;
+
+  TrapIds trap_ids_;            // Maps from TrapKeys to numeric ids
+  TrapKey* trap_array_;         // Array of TrapKeys indexed by ids
+  size_t trap_array_size_;      // Currently used size of array
+  size_t trap_array_capacity_;  // Currently allocated capacity of array
+  bool has_unsafe_traps_;       // Whether unsafe traps have been enabled
+
+  // Copying and assigning is unimplemented. It doesn't make sense for a
+  // singleton.
+  DISALLOW_COPY_AND_ASSIGN(Trap);
+};
+
+}  // namespace sandbox
+
+#endif  // SANDBOX_LINUX_SECCOMP_BPF_TRAP_H__