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// 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_SANDBOX_BPF_H_
#define SANDBOX_LINUX_SECCOMP_BPF_SANDBOX_BPF_H_
#include <stdint.h>
#include "base/files/scoped_file.h"
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "sandbox/linux/bpf_dsl/codegen.h"
#include "sandbox/sandbox_export.h"
namespace sandbox {
struct arch_seccomp_data;
namespace bpf_dsl {
class Policy;
}
// This class can be used to apply a syscall sandboxing policy expressed in a
// bpf_dsl::Policy object to the current process.
// Syscall sandboxing policies get inherited by subprocesses and, once applied,
// can never be removed for the lifetime of the process.
class SANDBOX_EXPORT SandboxBPF {
public:
enum class SeccompLevel {
SINGLE_THREADED,
MULTI_THREADED,
};
// Ownership of |policy| is transfered here to the sandbox object.
// nullptr is allowed for unit tests.
explicit SandboxBPF(bpf_dsl::Policy* policy);
// NOTE: Setting a policy and starting the sandbox is a one-way operation.
// The kernel does not provide any option for unloading a loaded sandbox. The
// sandbox remains engaged even when the object is destructed.
~SandboxBPF();
// Detect if the kernel supports the specified seccomp level.
// See StartSandbox() for a description of these.
static bool SupportsSeccompSandbox(SeccompLevel level);
// This is the main public entry point. It sets up the resources needed by
// the sandbox, and enters Seccomp mode.
// The calling process must provide a |level| to tell the sandbox which type
// of kernel support it should engage.
// SINGLE_THREADED will only sandbox the calling thread. Since it would be a
// security risk, the sandbox will also check that the current process is
// single threaded and crash if it isn't the case.
// MULTI_THREADED requires more recent kernel support and allows to sandbox
// all the threads of the current process. Be mindful of potential races,
// with other threads using disallowed system calls either before or after
// the sandbox is engaged.
//
// It is possible to stack multiple sandboxes by creating separate "Sandbox"
// objects and calling "StartSandbox()" on each of them. Please note, that
// this requires special care, though, as newly stacked sandboxes can never
// relax restrictions imposed by earlier sandboxes. Furthermore, installing
// a new policy requires making system calls, that might already be
// disallowed.
// Finally, stacking does add more kernel overhead than having a single
// combined policy. So, it should only be used if there are no alternatives.
bool StartSandbox(SeccompLevel level) WARN_UNUSED_RESULT;
// The sandbox needs to be able to access files in "/proc/self/". If
// this directory is not accessible when "StartSandbox()" gets called, the
// caller must provide an already opened file descriptor by calling
// "SetProcFd()".
// The sandbox becomes the new owner of this file descriptor and will
// close it when "StartSandbox()" executes or when the sandbox object
// disappears.
void SetProcFd(base::ScopedFD proc_fd);
// Checks whether a particular system call number is valid on the current
// architecture.
static bool IsValidSyscallNumber(int sysnum);
// UnsafeTraps require some syscalls to always be allowed.
// This helper function returns true for these calls.
static bool IsRequiredForUnsafeTrap(int sysno);
// From within an UnsafeTrap() it is often useful to be able to execute
// the system call that triggered the trap. The ForwardSyscall() method
// makes this easy. It is more efficient than calling glibc's syscall()
// function, as it avoid the extra round-trip to the signal handler. And
// it automatically does the correct thing to report kernel-style error
// conditions, rather than setting errno. See the comments for TrapFnc for
// details. In other words, the return value from ForwardSyscall() is
// directly suitable as a return value for a trap handler.
static intptr_t ForwardSyscall(const struct arch_seccomp_data& args);
// Assembles a BPF filter program from the current policy. After calling this
// function, you must not call any other sandboxing function.
// Typically, AssembleFilter() is only used by unit tests and by sandbox
// internals. It should not be used by production code.
// For performance reasons, we normally only run the assembled BPF program
// through the verifier, iff the program was built in debug mode.
// But by setting "force_verification", the caller can request that the
// verifier is run unconditionally. This is useful for unittests.
scoped_ptr<CodeGen::Program> AssembleFilter(bool force_verification);
private:
// Assembles and installs a filter based on the policy that has previously
// been configured with SetSandboxPolicy().
void InstallFilter(bool must_sync_threads);
base::ScopedFD proc_fd_;
bool sandbox_has_started_;
scoped_ptr<bpf_dsl::Policy> policy_;
DISALLOW_COPY_AND_ASSIGN(SandboxBPF);
};
} // namespace sandbox
#endif // SANDBOX_LINUX_SECCOMP_BPF_SANDBOX_BPF_H_
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