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// Copyright 2018 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package linux
import (
"syscall"
"gvisor.googlesource.com/gvisor/pkg/abi/linux"
"gvisor.googlesource.com/gvisor/pkg/bpf"
"gvisor.googlesource.com/gvisor/pkg/sentry/arch"
"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
)
// userSockFprog is equivalent to Linux's struct sock_fprog on amd64.
type userSockFprog struct {
// Len is the length of the filter in BPF instructions.
Len uint16
_ [6]byte // padding for alignment
// Filter is a user pointer to the struct sock_filter array that makes up
// the filter program. Filter is a uint64 rather than a usermem.Addr
// because usermem.Addr is actually uintptr, which is not a fixed-size
// type, and encoding/binary.Read objects to this.
Filter uint64
}
// seccomp applies a seccomp policy to the current task.
func seccomp(t *kernel.Task, mode, flags uint64, addr usermem.Addr) error {
// We only support SECCOMP_SET_MODE_FILTER at the moment.
if mode != linux.SECCOMP_SET_MODE_FILTER {
// Unsupported mode.
return syscall.EINVAL
}
tsync := flags&linux.SECCOMP_FILTER_FLAG_TSYNC != 0
// The only flag we support now is SECCOMP_FILTER_FLAG_TSYNC.
if flags&^linux.SECCOMP_FILTER_FLAG_TSYNC != 0 {
// Unsupported flag.
return syscall.EINVAL
}
var fprog userSockFprog
if _, err := t.CopyIn(addr, &fprog); err != nil {
return err
}
filter := make([]linux.BPFInstruction, int(fprog.Len))
if _, err := t.CopyIn(usermem.Addr(fprog.Filter), &filter); err != nil {
return err
}
compiledFilter, err := bpf.Compile(filter)
if err != nil {
t.Debugf("Invalid seccomp-bpf filter: %v", err)
return syscall.EINVAL
}
err = t.AppendSyscallFilter(compiledFilter)
if err == nil && tsync {
// Now we must copy this seccomp program to all other threads.
err = t.SyncSyscallFiltersToThreadGroup()
}
return err
}
// Seccomp implements linux syscall seccomp(2).
func Seccomp(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
return 0, nil, seccomp(t, args[0].Uint64(), args[1].Uint64(), args[2].Pointer())
}
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