github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/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/MerlinKodo/gvisor/pkg/context"
    19  	"github.com/MerlinKodo/gvisor/pkg/errors/linuxerr"
    20  	"github.com/MerlinKodo/gvisor/pkg/hostarch"
    21  	"github.com/MerlinKodo/gvisor/pkg/sentry/kernel/shm"
    22  	"github.com/MerlinKodo/gvisor/pkg/sentry/memmap"
    23  )
    24  
    25  // DetachShm unmaps a sysv shared memory segment.
    26  func (mm *MemoryManager) DetachShm(ctx context.Context, addr hostarch.Addr) error {
    27  	if addr != addr.RoundDown() {
    28  		// "... shmaddr is not aligned on a page boundary." - man shmdt(2)
    29  		return linuxerr.EINVAL
    30  	}
    31  
    32  	var detached *shm.Shm
    33  	var vgap vmaGapIterator
    34  
    35  	var droppedIDs []memmap.MappingIdentity
    36  	// This must run after mm.mappingMu.Unlock().
    37  	defer func() {
    38  		for _, id := range droppedIDs {
    39  			id.DecRef(ctx)
    40  		}
    41  	}()
    42  
    43  	mm.mappingMu.Lock()
    44  	defer mm.mappingMu.Unlock()
    45  
    46  	// Find and remove the first vma containing an address >= addr that maps a
    47  	// segment originally attached at addr.
    48  	vseg := mm.vmas.LowerBoundSegment(addr)
    49  	for vseg.Ok() {
    50  		vma := vseg.ValuePtr()
    51  		if shm, ok := vma.mappable.(*shm.Shm); ok && vseg.Start() >= addr && uint64(vseg.Start()-addr) == vma.off {
    52  			detached = shm
    53  			vgap, droppedIDs = mm.unmapLocked(ctx, vseg.Range(), droppedIDs)
    54  			vseg = vgap.NextSegment()
    55  			break
    56  		} else {
    57  			vseg = vseg.NextSegment()
    58  		}
    59  	}
    60  
    61  	if detached == nil {
    62  		// There is no shared memory segment attached at addr.
    63  		return linuxerr.EINVAL
    64  	}
    65  
    66  	// Remove all vmas that could have been created by the same attach.
    67  	end := addr + hostarch.Addr(detached.EffectiveSize())
    68  	for vseg.Ok() && vseg.End() <= end {
    69  		vma := vseg.ValuePtr()
    70  		if vma.mappable == detached && uint64(vseg.Start()-addr) == vma.off {
    71  			vgap, droppedIDs = mm.unmapLocked(ctx, vseg.Range(), droppedIDs)
    72  			vseg = vgap.NextSegment()
    73  		} else {
    74  			vseg = vseg.NextSegment()
    75  		}
    76  	}
    77  
    78  	return nil
    79  }