sandbox/linux/seccomp-bpf/trap.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef SANDBOX_LINUX_SECCOMP_BPF_TRAP_H__
   6 #define SANDBOX_LINUX_SECCOMP_BPF_TRAP_H__
   7
   8 #include <stdint.h>
   9
  10 #include <map>
  11
  12 #include "base/macros.h"
  13 #include "sandbox/linux/bpf_dsl/trap_registry.h"
  14 #include "sandbox/linux/system_headers/linux_signal.h"
  15 #include "sandbox/sandbox_export.h"
  16
  17 namespace sandbox {
  18
  19 // The Trap class allows a BPF filter program to branch out to user space by
  20 // raising a SIGSYS signal.
  21 // N.B.: This class does not perform any synchronization operations. If
  22 //   modifications are made to any of the traps, it is the caller's
  23 //   responsibility to ensure that this happens in a thread-safe fashion.
  24 //   Preferably, that means that no other threads should be running at that
  25 //   time. For the purposes of our sandbox, this assertion should always be
  26 //   true. Threads are incompatible with the seccomp sandbox anyway.
  27 class SANDBOX_EXPORT Trap : public bpf_dsl::TrapRegistry {
  28  public:
  29   uint16_t Add(TrapFnc fnc, const void* aux, bool safe) override;
  30
  31   bool EnableUnsafeTraps() override;
  32
  33   // Registry returns the trap registry used by Trap's SIGSYS handler,
  34   // creating it if necessary.
  35   static bpf_dsl::TrapRegistry* Registry();
  36
  37   // SandboxDebuggingAllowedByUser returns whether the
  38   // "CHROME_SANDBOX_DEBUGGING" environment variable is set.
  39   static bool SandboxDebuggingAllowedByUser();
  40
  41  private:
  42   struct TrapKey {
  43     TrapKey() : fnc(NULL), aux(NULL), safe(false) {}
  44     TrapKey(TrapFnc f, const void* a, bool s) : fnc(f), aux(a), safe(s) {}
  45     TrapFnc fnc;
  46     const void* aux;
  47     bool safe;
  48     bool operator<(const TrapKey&) const;
  49   };
  50   typedef std::map<TrapKey, uint16_t> TrapIds;
  51
  52   // Our constructor is private. A shared global instance is created
  53   // automatically as needed.
  54   Trap();
  55
  56   // The destructor is unimplemented as destroying this object would
  57   // break subsequent system calls that trigger a SIGSYS.
  58   ~Trap() = delete;
  59
  60   static void SigSysAction(int nr, LinuxSigInfo* info, void* void_context);
  61
  62   // Make sure that SigSys is not inlined in order to get slightly better crash
  63   // dumps.
  64   void SigSys(int nr, LinuxSigInfo* info, ucontext_t* ctx)
  65       __attribute__((noinline));
  66   // We have a global singleton that handles all of our SIGSYS traps. This
  67   // variable must never be deallocated after it has been set up initially, as
  68   // there is no way to reset in-kernel BPF filters that generate SIGSYS
  69   // events.
  70   static Trap* global_trap_;
  71
  72   TrapIds trap_ids_;            // Maps from TrapKeys to numeric ids
  73   TrapKey* trap_array_;         // Array of TrapKeys indexed by ids
  74   size_t trap_array_size_;      // Currently used size of array
  75   size_t trap_array_capacity_;  // Currently allocated capacity of array
  76   bool has_unsafe_traps_;       // Whether unsafe traps have been enabled
  77
  78   // Copying and assigning is unimplemented. It doesn't make sense for a
  79   // singleton.
  80   DISALLOW_COPY_AND_ASSIGN(Trap);
  81 };
  82
  83 }  // namespace sandbox
  84
  85 #endif  // SANDBOX_LINUX_SECCOMP_BPF_TRAP_H__