gvisor.dev/gvisor@v0.0.0-20240520182842-f9d4d51c7e0f/pkg/sentry/syscalls/linux/sys_random.go (about)

     1  // Copyright 2018 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package linux
    16  
    17  import (
    18  	"math"
    19  
    20  	"gvisor.dev/gvisor/pkg/errors/linuxerr"
    21  	"gvisor.dev/gvisor/pkg/hostarch"
    22  	"gvisor.dev/gvisor/pkg/rand"
    23  	"gvisor.dev/gvisor/pkg/safemem"
    24  	"gvisor.dev/gvisor/pkg/sentry/arch"
    25  	"gvisor.dev/gvisor/pkg/sentry/kernel"
    26  	"gvisor.dev/gvisor/pkg/usermem"
    27  )
    28  
    29  const (
    30  	_GRND_NONBLOCK = 0x1
    31  	_GRND_RANDOM   = 0x2
    32  )
    33  
    34  // GetRandom implements the linux syscall getrandom(2).
    35  //
    36  // In a multi-tenant/shared environment, the only valid implementation is to
    37  // fetch data from the urandom pool, otherwise starvation attacks become
    38  // possible. The urandom pool is also expected to have plenty of entropy, thus
    39  // the GRND_RANDOM flag is ignored. The GRND_NONBLOCK flag does not apply, as
    40  // the pool will already be initialized.
    41  func GetRandom(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
    42  	addr := args[0].Pointer()
    43  	length := args[1].SizeT()
    44  	flags := args[2].Int()
    45  
    46  	// Flags are checked for validity but otherwise ignored. See above.
    47  	if flags & ^(_GRND_NONBLOCK|_GRND_RANDOM) != 0 {
    48  		return 0, nil, linuxerr.EINVAL
    49  	}
    50  
    51  	if length > math.MaxInt32 {
    52  		length = math.MaxInt32
    53  	}
    54  	ar, ok := addr.ToRange(uint64(length))
    55  	if !ok {
    56  		return 0, nil, linuxerr.EFAULT
    57  	}
    58  
    59  	n, err := t.MemoryManager().CopyOutFrom(t, hostarch.AddrRangeSeqOf(ar), safemem.FromIOReader{rand.Reader}, usermem.IOOpts{
    60  		AddressSpaceActive: true,
    61  	})
    62  	if n > 0 {
    63  		return uintptr(n), nil, nil
    64  	}
    65  	return 0, nil, err
    66  }