Pass information about map writableness to filesystems.

This is necessary to implement file seals for memfds.

PiperOrigin-RevId: 225239394
Change-Id: Ib3f1ab31385afc4b24e96cd81a05ef1bebbcbb70

6 files changed, 15 insertions, 11 deletions

diff --git a/pkg/sentry/mm/aio_context.go b/pkg/sentry/mm/aio_context.go
index 87942af0e..5e86d3b49 100644
--- a/pkg/sentry/mm/aio_context.go
+++ b/pkg/sentry/mm/aio_context.go
@@ -244,7 +244,7 @@ func (m *aioMappable) Msync(ctx context.Context, mr memmap.MappableRange) error
 }
 
 // AddMapping implements memmap.Mappable.AddMapping.
-func (m *aioMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64) error {
+func (m *aioMappable) AddMapping(_ context.Context, _ memmap.MappingSpace, ar usermem.AddrRange, offset uint64, _ bool) error {
 	// Don't allow mappings to be expanded (in Linux, fs/aio.c:aio_ring_mmap()
 	// sets VM_DONTEXPAND).
 	if offset != 0 || uint64(ar.Length()) != aioRingBufferSize {
@@ -254,11 +254,11 @@ func (m *aioMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar
 }
 
 // RemoveMapping implements memmap.Mappable.RemoveMapping.
-func (m *aioMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64) {
+func (m *aioMappable) RemoveMapping(context.Context, memmap.MappingSpace, usermem.AddrRange, uint64, bool) {
 }
 
 // CopyMapping implements memmap.Mappable.CopyMapping.
-func (m *aioMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64) error {
+func (m *aioMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, _ bool) error {
 	// Don't allow mappings to be expanded (in Linux, fs/aio.c:aio_ring_mmap()
 	// sets VM_DONTEXPAND).
 	if offset != 0 || uint64(dstAR.Length()) != aioRingBufferSize {
diff --git a/pkg/sentry/mm/lifecycle.go b/pkg/sentry/mm/lifecycle.go
index b248b76e7..1613ce11d 100644
--- a/pkg/sentry/mm/lifecycle.go
+++ b/pkg/sentry/mm/lifecycle.go
@@ -81,7 +81,7 @@ func (mm *MemoryManager) Fork(ctx context.Context) (*MemoryManager, error) {
 		vmaAR := srcvseg.Range()
 		// Inform the Mappable, if any, of the new mapping.
 		if vma.mappable != nil {
-			if err := vma.mappable.AddMapping(ctx, mm2, vmaAR, vma.off); err != nil {
+			if err := vma.mappable.AddMapping(ctx, mm2, vmaAR, vma.off, vma.isMappableAsWritable()); err != nil {
 				mm2.removeVMAsLocked(ctx, mm2.applicationAddrRange())
 				return nil, err
 			}
diff --git a/pkg/sentry/mm/mm.go b/pkg/sentry/mm/mm.go
index aab697f9e..b1e39e898 100644
--- a/pkg/sentry/mm/mm.go
+++ b/pkg/sentry/mm/mm.go
@@ -349,6 +349,10 @@ func (v *vma) loadRealPerms(b int) {
 	}
 }
 
+func (v *vma) isMappableAsWritable() bool {
+	return !v.private && v.maxPerms.Write
+}
+
 // pma represents a platform mapping area.
 //
 // +stateify savable
diff --git a/pkg/sentry/mm/special_mappable.go b/pkg/sentry/mm/special_mappable.go
index e511472f4..64d0dd3f6 100644
--- a/pkg/sentry/mm/special_mappable.go
+++ b/pkg/sentry/mm/special_mappable.go
@@ -76,16 +76,16 @@ func (m *SpecialMappable) Msync(ctx context.Context, mr memmap.MappableRange) er
 }
 
 // AddMapping implements memmap.Mappable.AddMapping.
-func (m *SpecialMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64) error {
+func (*SpecialMappable) AddMapping(context.Context, memmap.MappingSpace, usermem.AddrRange, uint64, bool) error {
 	return nil
 }
 
 // RemoveMapping implements memmap.Mappable.RemoveMapping.
-func (m *SpecialMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64) {
+func (*SpecialMappable) RemoveMapping(context.Context, memmap.MappingSpace, usermem.AddrRange, uint64, bool) {
 }
 
 // CopyMapping implements memmap.Mappable.CopyMapping.
-func (m *SpecialMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64) error {
+func (*SpecialMappable) CopyMapping(context.Context, memmap.MappingSpace, usermem.AddrRange, usermem.AddrRange, uint64, bool) error {
 	return nil
 }
 
diff --git a/pkg/sentry/mm/syscalls.go b/pkg/sentry/mm/syscalls.go
index 1a46c2105..daaae4da1 100644
--- a/pkg/sentry/mm/syscalls.go
+++ b/pkg/sentry/mm/syscalls.go
@@ -443,7 +443,7 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi
 			return 0, syserror.EINVAL
 		}
 		// Inform the Mappable, if any, of the new mapping.
-		if err := vma.mappable.CopyMapping(ctx, mm, oldAR, newAR, vseg.mappableOffsetAt(oldAR.Start)); err != nil {
+		if err := vma.mappable.CopyMapping(ctx, mm, oldAR, newAR, vseg.mappableOffsetAt(oldAR.Start), vma.isMappableAsWritable()); err != nil {
 			return 0, err
 		}
 	}
@@ -498,7 +498,7 @@ func (mm *MemoryManager) MRemap(ctx context.Context, oldAddr usermem.Addr, oldSi
 	// Now that pmas have been moved to newAR, we can notify vma.mappable that
 	// oldAR is no longer mapped.
 	if vma.mappable != nil {
-		vma.mappable.RemoveMapping(ctx, mm, oldAR, vma.off)
+		vma.mappable.RemoveMapping(ctx, mm, oldAR, vma.off, vma.isMappableAsWritable())
 	}
 
 	return newAR.Start, nil
diff --git a/pkg/sentry/mm/vma.go b/pkg/sentry/mm/vma.go
index dafdbd0e4..5c2c802f6 100644
--- a/pkg/sentry/mm/vma.go
+++ b/pkg/sentry/mm/vma.go
@@ -65,7 +65,7 @@ func (mm *MemoryManager) createVMALocked(ctx context.Context, opts memmap.MMapOp
 
 	// Inform the Mappable, if any, of the new mapping.
 	if opts.Mappable != nil {
-		if err := opts.Mappable.AddMapping(ctx, mm, ar, opts.Offset); err != nil {
+		if err := opts.Mappable.AddMapping(ctx, mm, ar, opts.Offset, !opts.Private && opts.MaxPerms.Write); err != nil {
 			return vmaIterator{}, usermem.AddrRange{}, err
 		}
 	}
@@ -332,7 +332,7 @@ func (mm *MemoryManager) removeVMAsLocked(ctx context.Context, ar usermem.AddrRa
 		vmaAR := vseg.Range()
 		vma := vseg.ValuePtr()
 		if vma.mappable != nil {
-			vma.mappable.RemoveMapping(ctx, mm, vmaAR, vma.off)
+			vma.mappable.RemoveMapping(ctx, mm, vmaAR, vma.off, vma.isMappableAsWritable())
 		}
 		if vma.id != nil {
 			vma.id.DecRef()