1 files changed, 147 insertions, 0 deletions
diff --git a/pkg/sentry/mm/special_mappable.go b/pkg/sentry/mm/special_mappable.go
new file mode 100644
index 000000000..9d3614034
--- /dev/null
+++ b/pkg/sentry/mm/special_mappable.go
@@ -0,0 +1,147 @@
+// Copyright 2018 Google Inc.
+//
+// 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 mm
+
+import (
+	"gvisor.googlesource.com/gvisor/pkg/refs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usage"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+	"gvisor.googlesource.com/gvisor/pkg/syserror"
+)
+
+// SpecialMappable implements memmap.MappingIdentity and memmap.Mappable with
+// semantics similar to Linux's mm/mmap.c:_install_special_mapping(), except
+// that SpecialMappable takes ownership of the memory that it represents
+// (_install_special_mapping() does not.)
+type SpecialMappable struct {
+	refs.AtomicRefCount
+
+	p    platform.Platform
+	fr   platform.FileRange
+	name string
+}
+
+// NewSpecialMappable returns a SpecialMappable that owns fr, which represents
+// offsets in p.Memory() that contain the SpecialMappable's data. The
+// SpecialMappable will use the given name in /proc/[pid]/maps.
+//
+// Preconditions: fr.Length() != 0.
+func NewSpecialMappable(name string, p platform.Platform, fr platform.FileRange) *SpecialMappable {
+	return &SpecialMappable{p: p, fr: fr, name: name}
+}
+
+// DecRef implements refs.RefCounter.DecRef.
+func (m *SpecialMappable) DecRef() {
+	m.AtomicRefCount.DecRefWithDestructor(func() {
+		m.p.Memory().DecRef(m.fr)
+	})
+}
+
+// MappedName implements memmap.MappingIdentity.MappedName.
+func (m *SpecialMappable) MappedName(ctx context.Context) string {
+	return m.name
+}
+
+// DeviceID implements memmap.MappingIdentity.DeviceID.
+func (m *SpecialMappable) DeviceID() uint64 {
+	return 0
+}
+
+// InodeID implements memmap.MappingIdentity.InodeID.
+func (m *SpecialMappable) InodeID() uint64 {
+	return 0
+}
+
+// Msync implements memmap.MappingIdentity.Msync.
+func (m *SpecialMappable) Msync(ctx context.Context, mr memmap.MappableRange) error {
+	// Linux: vm_file is NULL, causing msync to skip it entirely.
+	return nil
+}
+
+// AddMapping implements memmap.Mappable.AddMapping.
+func (m *SpecialMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64) error {
+	return nil
+}
+
+// RemoveMapping implements memmap.Mappable.RemoveMapping.
+func (m *SpecialMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64) {
+}
+
+// CopyMapping implements memmap.Mappable.CopyMapping.
+func (m *SpecialMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64) error {
+	return nil
+}
+
+// Translate implements memmap.Mappable.Translate.
+func (m *SpecialMappable) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
+	var err error
+	if required.End > m.fr.Length() {
+		err = &memmap.BusError{syserror.EFAULT}
+	}
+	if source := optional.Intersect(memmap.MappableRange{0, m.fr.Length()}); source.Length() != 0 {
+		return []memmap.Translation{
+			{
+				Source: source,
+				File:   m.p.Memory(),
+				Offset: m.fr.Start + source.Start,
+			},
+		}, err
+	}
+	return nil, err
+}
+
+// InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
+func (m *SpecialMappable) InvalidateUnsavable(ctx context.Context) error {
+	// Since data is stored in platform.Platform.Memory(), the contents of
+	// which are preserved across save/restore, we don't need to do anything.
+	return nil
+}
+
+// Platform returns the Platform whose Memory stores the SpecialMappable's
+// contents.
+func (m *SpecialMappable) Platform() platform.Platform {
+	return m.p
+}
+
+// FileRange returns the offsets into Platform().Memory() that store the
+// SpecialMappable's contents.
+func (m *SpecialMappable) FileRange() platform.FileRange {
+	return m.fr
+}
+
+// Length returns the length of the SpecialMappable.
+func (m *SpecialMappable) Length() uint64 {
+	return m.fr.Length()
+}
+
+// NewSharedAnonMappable returns a SpecialMappable that implements the
+// semantics of mmap(MAP_SHARED|MAP_ANONYMOUS) and mappings of /dev/zero.
+//
+// TODO: The use of SpecialMappable is a lazy code reuse hack. Linux
+// uses an ephemeral file created by mm/shmem.c:shmem_zero_setup(); we should
+// do the same to get non-zero device and inode IDs.
+func NewSharedAnonMappable(length uint64, p platform.Platform) (*SpecialMappable, error) {
+	if length == 0 || length != uint64(usermem.Addr(length).RoundDown()) {
+		return nil, syserror.EINVAL
+	}
+	fr, err := p.Memory().Allocate(length, usage.Anonymous)
+	if err != nil {
+		return nil, err
+	}
+	return NewSpecialMappable("/dev/zero (deleted)", p, fr), nil
+}