1 files changed, 197 insertions, 0 deletions
diff --git a/pkg/sentry/fs/fsutil/host_mappable.go b/pkg/sentry/fs/fsutil/host_mappable.go
new file mode 100644
index 000000000..ad0518b8f
--- /dev/null
+++ b/pkg/sentry/fs/fsutil/host_mappable.go
@@ -0,0 +1,197 @@
+// Copyright 2019 The gVisor Authors.
+//
+// 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 fsutil
+
+import (
+	"math"
+	"sync"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/memmap"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+)
+
+// HostMappable implements memmap.Mappable and platform.File over a
+// CachedFileObject.
+//
+// Lock order (compare the lock order model in mm/mm.go):
+//   truncateMu ("fs locks")
+//     mu ("memmap.Mappable locks not taken by Translate")
+//       ("platform.File locks")
+//   	     backingFile ("CachedFileObject locks")
+//
+// +stateify savable
+type HostMappable struct {
+	hostFileMapper *HostFileMapper
+
+	backingFile CachedFileObject
+
+	mu sync.Mutex `state:"nosave"`
+
+	// mappings tracks mappings of the cached file object into
+	// memmap.MappingSpaces so it can invalidated upon save. Protected by mu.
+	mappings memmap.MappingSet
+
+	// truncateMu protects writes and truncations. See Truncate() for details.
+	truncateMu sync.RWMutex `state:"nosave"`
+}
+
+// NewHostMappable creates a new mappable that maps directly to host FD.
+func NewHostMappable(backingFile CachedFileObject) *HostMappable {
+	return &HostMappable{
+		hostFileMapper: NewHostFileMapper(),
+		backingFile:    backingFile,
+	}
+}
+
+// AddMapping implements memmap.Mappable.AddMapping.
+func (h *HostMappable) AddMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) error {
+	// Hot path. Avoid defers.
+	h.mu.Lock()
+	mapped := h.mappings.AddMapping(ms, ar, offset, writable)
+	for _, r := range mapped {
+		h.hostFileMapper.IncRefOn(r)
+	}
+	h.mu.Unlock()
+	return nil
+}
+
+// RemoveMapping implements memmap.Mappable.RemoveMapping.
+func (h *HostMappable) RemoveMapping(ctx context.Context, ms memmap.MappingSpace, ar usermem.AddrRange, offset uint64, writable bool) {
+	// Hot path. Avoid defers.
+	h.mu.Lock()
+	unmapped := h.mappings.RemoveMapping(ms, ar, offset, writable)
+	for _, r := range unmapped {
+		h.hostFileMapper.DecRefOn(r)
+	}
+	h.mu.Unlock()
+}
+
+// CopyMapping implements memmap.Mappable.CopyMapping.
+func (h *HostMappable) CopyMapping(ctx context.Context, ms memmap.MappingSpace, srcAR, dstAR usermem.AddrRange, offset uint64, writable bool) error {
+	return h.AddMapping(ctx, ms, dstAR, offset, writable)
+}
+
+// Translate implements memmap.Mappable.Translate.
+func (h *HostMappable) Translate(ctx context.Context, required, optional memmap.MappableRange, at usermem.AccessType) ([]memmap.Translation, error) {
+	return []memmap.Translation{
+		{
+			Source: optional,
+			File:   h,
+			Offset: optional.Start,
+			Perms:  usermem.AnyAccess,
+		},
+	}, nil
+}
+
+// InvalidateUnsavable implements memmap.Mappable.InvalidateUnsavable.
+func (h *HostMappable) InvalidateUnsavable(ctx context.Context) error {
+	h.mu.Lock()
+	h.mappings.InvalidateAll(memmap.InvalidateOpts{})
+	h.mu.Unlock()
+	return nil
+}
+
+// MapInternal implements platform.File.MapInternal.
+func (h *HostMappable) MapInternal(fr platform.FileRange, at usermem.AccessType) (safemem.BlockSeq, error) {
+	return h.hostFileMapper.MapInternal(fr, h.backingFile.FD(), at.Write)
+}
+
+// FD implements platform.File.FD.
+func (h *HostMappable) FD() int {
+	return h.backingFile.FD()
+}
+
+// IncRef implements platform.File.IncRef.
+func (h *HostMappable) IncRef(fr platform.FileRange) {
+	mr := memmap.MappableRange{Start: fr.Start, End: fr.End}
+	h.hostFileMapper.IncRefOn(mr)
+}
+
+// DecRef implements platform.File.DecRef.
+func (h *HostMappable) DecRef(fr platform.FileRange) {
+	mr := memmap.MappableRange{Start: fr.Start, End: fr.End}
+	h.hostFileMapper.DecRefOn(mr)
+}
+
+// Truncate truncates the file, invalidating any mapping that may have been
+// removed after the size change.
+//
+// Truncation and writes are synchronized to prevent races where writes make the
+// file grow between truncation and invalidation below:
+//   T1: Calls SetMaskedAttributes and stalls
+//   T2: Appends to file causing it to grow
+//   T2: Writes to mapped pages and COW happens
+//   T1: Continues and wronly invalidates the page mapped in step above.
+func (h *HostMappable) Truncate(ctx context.Context, newSize int64) error {
+	h.truncateMu.Lock()
+	defer h.truncateMu.Unlock()
+
+	mask := fs.AttrMask{Size: true}
+	attr := fs.UnstableAttr{Size: newSize}
+	if err := h.backingFile.SetMaskedAttributes(ctx, mask, attr); err != nil {
+		return err
+	}
+
+	// Invalidate COW mappings that may exist beyond the new size in case the file
+	// is being shrunk. Other mappings don't need to be invalidated because
+	// translate will just return identical mappings after invalidation anyway,
+	// and SIGBUS will be raised and handled when the mappings are touched.
+	//
+	// Compare Linux's mm/truncate.c:truncate_setsize() =>
+	// truncate_pagecache() =>
+	// mm/memory.c:unmap_mapping_range(evencows=1).
+	h.mu.Lock()
+	defer h.mu.Unlock()
+	mr := memmap.MappableRange{
+		Start: fs.OffsetPageEnd(newSize),
+		End:   fs.OffsetPageEnd(math.MaxInt64),
+	}
+	h.mappings.Invalidate(mr, memmap.InvalidateOpts{InvalidatePrivate: true})
+
+	return nil
+}
+
+// Allocate reserves space in the backing file.
+func (h *HostMappable) Allocate(ctx context.Context, offset int64, length int64) error {
+	h.truncateMu.RLock()
+	err := h.backingFile.Allocate(ctx, offset, length)
+	h.truncateMu.RUnlock()
+	return err
+}
+
+// Write writes to the file backing this mappable.
+func (h *HostMappable) Write(ctx context.Context, src usermem.IOSequence, offset int64) (int64, error) {
+	h.truncateMu.RLock()
+	n, err := src.CopyInTo(ctx, &writer{ctx: ctx, hostMappable: h, off: offset})
+	h.truncateMu.RUnlock()
+	return n, err
+}
+
+type writer struct {
+	ctx          context.Context
+	hostMappable *HostMappable
+	off          int64
+}
+
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
+func (w *writer) WriteFromBlocks(src safemem.BlockSeq) (uint64, error) {
+	n, err := w.hostMappable.backingFile.WriteFromBlocksAt(w.ctx, src, uint64(w.off))
+	w.off += int64(n)
+	return n, err
+}