github.com/SagerNet/gvisor@v0.0.0-20210707092255-7731c139d75c/pkg/sentry/mm/shm.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 mm
    16  
    17  import (
    18  	"github.com/SagerNet/gvisor/pkg/context"
    19  	"github.com/SagerNet/gvisor/pkg/errors/linuxerr"
    20  	"github.com/SagerNet/gvisor/pkg/hostarch"
    21  	"github.com/SagerNet/gvisor/pkg/sentry/kernel/shm"
    22  )
    23  
    24  // DetachShm unmaps a sysv shared memory segment.
    25  func (mm *MemoryManager) DetachShm(ctx context.Context, addr hostarch.Addr) error {
    26  	if addr != addr.RoundDown() {
    27  		// "... shmaddr is not aligned on a page boundary." - man shmdt(2)
    28  		return linuxerr.EINVAL
    29  	}
    30  
    31  	var detached *shm.Shm
    32  	mm.mappingMu.Lock()
    33  	defer mm.mappingMu.Unlock()
    34  
    35  	// Find and remove the first vma containing an address >= addr that maps a
    36  	// segment originally attached at addr.
    37  	vseg := mm.vmas.LowerBoundSegment(addr)
    38  	for vseg.Ok() {
    39  		vma := vseg.ValuePtr()
    40  		if shm, ok := vma.mappable.(*shm.Shm); ok && vseg.Start() >= addr && uint64(vseg.Start()-addr) == vma.off {
    41  			detached = shm
    42  			vseg = mm.unmapLocked(ctx, vseg.Range()).NextSegment()
    43  			break
    44  		} else {
    45  			vseg = vseg.NextSegment()
    46  		}
    47  	}
    48  
    49  	if detached == nil {
    50  		// There is no shared memory segment attached at addr.
    51  		return linuxerr.EINVAL
    52  	}
    53  
    54  	// Remove all vmas that could have been created by the same attach.
    55  	end := addr + hostarch.Addr(detached.EffectiveSize())
    56  	for vseg.Ok() && vseg.End() <= end {
    57  		vma := vseg.ValuePtr()
    58  		if vma.mappable == detached && uint64(vseg.Start()-addr) == vma.off {
    59  			vseg = mm.unmapLocked(ctx, vseg.Range()).NextSegment()
    60  		} else {
    61  			vseg = vseg.NextSegment()
    62  		}
    63  	}
    64  
    65  	return nil
    66  }