| // 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__ |