Filesystems shouldn't be saving references to Platform.

Platform objects are not savable, storing references to them in
filesystem datastructures would cause save to fail if someone actually
passed in a Platform.

Current implementations work because everywhere a Platform is
expected, we currently pass in a Kernel object which embeds Platform
and thus satisfies the interface.

Eliminate this indirection and save pointers to Kernel directly.

PiperOrigin-RevId: 225288336
Change-Id: Ica399ff43f425e15bc150a0d7102196c3d54a2ab

pkg/sentry/context/contexttest/contexttest.go

@@ -31,23 +31,30 @@ import (
 
 // Context returns a Context that may be used in tests. Uses ptrace as the
 // platform.Platform.
+//
+// Note that some filesystems may require a minimal kernel for testing, which
+// this test context does not provide. For such tests, see kernel/contexttest.
 func Context(tb testing.TB) context.Context {
 	p, err := ptrace.New()
 	if err != nil {
 		tb.Fatal(err)
 	}
 	// Test usage of context.Background is fine.
-	return &testContext{
-		Context:  context.Background(),
-		l:        limits.NewLimitSet(),
-		platform: p,
+	return &TestContext{
+		Context:     context.Background(),
+		l:           limits.NewLimitSet(),
+		platform:    p,
+		otherValues: make(map[interface{}]interface{}),
 	}
 }
 
-type testContext struct {
+// TestContext represents a context with minimal functionality suitable for
+// running tests.
+type TestContext struct {
 	context.Context
-	l        *limits.LimitSet
-	platform platform.Platform
+	l           *limits.LimitSet
+	platform    platform.Platform
+	otherValues map[interface{}]interface{}
 }
 
 // globalUniqueID tracks incremental unique identifiers for tests.
@@ -76,8 +83,14 @@ func (hostClock) Now() ktime.Time {
 	return ktime.FromNanoseconds(time.Now().UnixNano())
 }
 
+// RegisterValue registers additional values with this test context. Useful for
+// providing values from external packages that contexttest can't depend on.
+func (t *TestContext) RegisterValue(key, value interface{}) {
+	t.otherValues[key] = value
+}
+
 // Value implements context.Context.
-func (t *testContext) Value(key interface{}) interface{} {
+func (t *TestContext) Value(key interface{}) interface{} {
 	switch key {
 	case limits.CtxLimits:
 		return t.l
@@ -92,6 +105,9 @@ func (t *testContext) Value(key interface{}) interface{} {
 	case ktime.CtxRealtimeClock:
 		return hostClock{}
 	default:
+		if val, ok := t.otherValues[key]; ok {
+			return val
+		}
 		return t.Context.Value(key)
 	}
 }

pkg/sentry/fs/BUILD

@@ -94,9 +94,9 @@ go_test(
     deps = [
         ":fs",
         "//pkg/sentry/context",
-        "//pkg/sentry/context/contexttest",
         "//pkg/sentry/fs/ramfs/test",
         "//pkg/sentry/fs/tmpfs",
+        "//pkg/sentry/kernel/contexttest",
         "//pkg/sentry/usermem",
         "//pkg/syserror",
     ],

pkg/sentry/fs/ashmem/area.go

@@ -23,8 +23,8 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/tmpfs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
 	"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"
@@ -117,11 +117,11 @@ func (a *Area) ConfigureMMap(ctx context.Context, file *fs.File, opts *memmap.MM
 	opts.MaxPerms = opts.MaxPerms.Intersect(a.perms)
 
 	if a.tmpfsFile == nil {
-		p := platform.FromContext(ctx)
-		if p == nil {
+		k := kernel.KernelFromContext(ctx)
+		if k == nil {
 			return syserror.ENOMEM
 		}
-		tmpfsInodeOps := tmpfs.NewInMemoryFile(ctx, usage.Tmpfs, fs.UnstableAttr{}, p)
+		tmpfsInodeOps := tmpfs.NewInMemoryFile(ctx, usage.Tmpfs, fs.UnstableAttr{}, k)
 		// This is not backed by a real filesystem, so we pass in nil.
 		tmpfsInode := fs.NewInode(tmpfsInodeOps, fs.NewNonCachingMountSource(nil, fs.MountSourceFlags{}), fs.StableAttr{})
 		dirent := fs.NewDirent(tmpfsInode, namePrefix+"/"+a.name)

pkg/sentry/fs/copy_up_test.go

@@ -22,9 +22,9 @@ import (
 	"sync"
 	"testing"
 
-	"gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	_ "gvisor.googlesource.com/gvisor/pkg/sentry/fs/tmpfs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
 )
 

pkg/sentry/fs/dev/BUILD

@@ -25,6 +25,7 @@ go_library(
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/fs/ramfs",
         "//pkg/sentry/fs/tmpfs",
+        "//pkg/sentry/kernel",
         "//pkg/sentry/memmap",
         "//pkg/sentry/mm",
         "//pkg/sentry/platform",

pkg/sentry/fs/dev/dev.go

@@ -22,7 +22,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/binder"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/tmpfs"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
 )
 
@@ -86,7 +86,7 @@ func New(ctx context.Context, msrc *fs.MountSource, binderEnabled bool, ashmemEn
 		"random":  newCharacterDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc),
 		"urandom": newCharacterDevice(newRandomDevice(ctx, fs.RootOwner, 0444), msrc),
 
-		"shm": tmpfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0777), msrc, platform.FromContext(ctx)),
+		"shm": tmpfs.NewDir(ctx, nil, fs.RootOwner, fs.FilePermsFromMode(0777), msrc, kernel.KernelFromContext(ctx)),
 
 		// A devpts is typically mounted at /dev/pts to provide
 		// pseudoterminal support. Place an empty directory there for

pkg/sentry/fs/file_overlay_test.go

@@ -19,9 +19,9 @@ import (
 	"testing"
 
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	ramfstest "gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs/test"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/contexttest"
 )
 
 func TestReaddir(t *testing.T) {

pkg/sentry/fs/inode_overlay_test.go

@@ -18,9 +18,9 @@ import (
 	"testing"
 
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	ramfstest "gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs/test"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/syserror"
 )
 

pkg/sentry/fs/mounts_test.go

@@ -18,9 +18,9 @@ import (
 	"testing"
 
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	ramfstest "gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs/test"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/contexttest"
 )
 
 // Creates a new MountNamespace with filesystem:

pkg/sentry/fs/tmpfs/BUILD

@@ -20,10 +20,10 @@ go_library(
         "//pkg/sentry/fs",
         "//pkg/sentry/fs/fsutil",
         "//pkg/sentry/fs/ramfs",
+        "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/kernel/pipe",
         "//pkg/sentry/memmap",
-        "//pkg/sentry/platform",
         "//pkg/sentry/safemem",
         "//pkg/sentry/socket/unix/transport",
         "//pkg/sentry/usage",
@@ -39,9 +39,9 @@ go_test(
     embed = [":tmpfs"],
     deps = [
         "//pkg/sentry/context",
-        "//pkg/sentry/context/contexttest",
         "//pkg/sentry/fs",
-        "//pkg/sentry/platform",
+        "//pkg/sentry/kernel",
+        "//pkg/sentry/kernel/contexttest",
         "//pkg/sentry/usage",
         "//pkg/sentry/usermem",
     ],

pkg/sentry/fs/tmpfs/file_test.go

@@ -19,16 +19,16 @@ import (
 	"testing"
 
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/contexttest"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usage"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
 )
 
 func newFileInode(ctx context.Context) *fs.Inode {
 	m := fs.NewCachingMountSource(&Filesystem{}, fs.MountSourceFlags{})
-	iops := NewInMemoryFile(ctx, usage.Tmpfs, fs.WithCurrentTime(ctx, fs.UnstableAttr{}), platform.FromContext(ctx))
+	iops := NewInMemoryFile(ctx, usage.Tmpfs, fs.WithCurrentTime(ctx, fs.UnstableAttr{}), kernel.KernelFromContext(ctx))
 	return fs.NewInode(iops, m, fs.StableAttr{
 		DeviceID:  tmpfsDevice.DeviceID(),
 		InodeID:   tmpfsDevice.NextIno(),

pkg/sentry/fs/tmpfs/fs.go

@@ -21,8 +21,8 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/auth"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
 )
 
 const (
@@ -131,5 +131,5 @@ func (f *Filesystem) Mount(ctx context.Context, device string, flags fs.MountSou
 	msrc := fs.NewCachingMountSource(f, flags)
 
 	// Construct the tmpfs root.
-	return NewDir(ctx, nil, owner, perms, msrc, platform.FromContext(ctx)), nil
+	return NewDir(ctx, nil, owner, perms, msrc, kernel.KernelFromContext(ctx)), nil
 }

pkg/sentry/fs/tmpfs/inode_file.go

@@ -21,8 +21,8 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
 	"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/usage"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
@@ -52,8 +52,8 @@ type fileInodeOperations struct {
 	fsutil.InodeNotSymlink          `state:"nosave"`
 	fsutil.NoopWriteOut             `state:"nosave"`
 
-	// platform is used to allocate memory that stores the file's contents.
-	platform platform.Platform
+	// kernel is used to allocate platform memory that stores the file's contents.
+	kernel *kernel.Kernel
 
 	// memUsage is the default memory usage that will be reported by this file.
 	memUsage usage.MemoryKind
@@ -84,12 +84,12 @@ type fileInodeOperations struct {
 }
 
 // NewInMemoryFile returns a new file backed by p.Memory().
-func NewInMemoryFile(ctx context.Context, usage usage.MemoryKind, uattr fs.UnstableAttr, p platform.Platform) fs.InodeOperations {
+func NewInMemoryFile(ctx context.Context, usage usage.MemoryKind, uattr fs.UnstableAttr, k *kernel.Kernel) fs.InodeOperations {
 	return &fileInodeOperations{
 		attr: fsutil.InMemoryAttributes{
 			Unstable: uattr,
 		},
-		platform: p,
+		kernel:   k,
 		memUsage: usage,
 	}
 }
@@ -98,7 +98,7 @@ func NewInMemoryFile(ctx context.Context, usage usage.MemoryKind, uattr fs.Unsta
 func (f *fileInodeOperations) Release(context.Context) {
 	f.dataMu.Lock()
 	defer f.dataMu.Unlock()
-	f.data.DropAll(f.platform.Memory())
+	f.data.DropAll(f.kernel.Platform.Memory())
 }
 
 // Mappable implements fs.InodeOperations.Mappable.
@@ -212,7 +212,7 @@ func (f *fileInodeOperations) Truncate(ctx context.Context, inode *fs.Inode, siz
 	// and can remove them.
 	f.dataMu.Lock()
 	defer f.dataMu.Unlock()
-	f.data.Truncate(uint64(size), f.platform.Memory())
+	f.data.Truncate(uint64(size), f.kernel.Platform.Memory())
 
 	return nil
 }
@@ -310,7 +310,7 @@ func (rw *fileReadWriter) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
 		return 0, nil
 	}
 
-	mem := rw.f.platform.Memory()
+	mem := rw.f.kernel.Platform.Memory()
 	var done uint64
 	seg, gap := rw.f.data.Find(uint64(rw.offset))
 	for rw.offset < end {
@@ -376,7 +376,7 @@ func (rw *fileReadWriter) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error)
 		}
 	}()
 
-	mem := rw.f.platform.Memory()
+	mem := rw.f.kernel.Platform.Memory()
 	// Page-aligned mr for when we need to allocate memory. RoundUp can't
 	// overflow since end is an int64.
 	pgstartaddr := usermem.Addr(rw.offset).RoundDown()
@@ -465,7 +465,7 @@ func (f *fileInodeOperations) Translate(ctx context.Context, required, optional
 		optional.End = pgend
 	}
 
-	mem := f.platform.Memory()
+	mem := f.kernel.Platform.Memory()
 	cerr := f.data.Fill(ctx, required, optional, mem, f.memUsage, func(_ context.Context, dsts safemem.BlockSeq, _ uint64) (uint64, error) {
 		// Newly-allocated pages are zeroed, so we don't need to do anything.
 		return dsts.NumBytes(), nil

pkg/sentry/fs/tmpfs/tmpfs.go

@@ -20,8 +20,8 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/ramfs"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel/pipe"
-	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/socket/unix/transport"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usage"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
@@ -54,13 +54,13 @@ func rename(ctx context.Context, oldParent *fs.Inode, oldName string, newParent
 type Dir struct {
 	ramfs.Dir
 
-	// platform is used to allocate storage for tmpfs Files.
-	platform platform.Platform
+	// kernel is used to allocate platform memory as storage for tmpfs Files.
+	kernel *kernel.Kernel
 }
 
 // NewDir returns a new directory.
-func NewDir(ctx context.Context, contents map[string]*fs.Inode, owner fs.FileOwner, perms fs.FilePermissions, msrc *fs.MountSource, platform platform.Platform) *fs.Inode {
-	d := &Dir{platform: platform}
+func NewDir(ctx context.Context, contents map[string]*fs.Inode, owner fs.FileOwner, perms fs.FilePermissions, msrc *fs.MountSource, kernel *kernel.Kernel) *fs.Inode {
+	d := &Dir{kernel: kernel}
 	d.InitDir(ctx, contents, owner, perms)
 
 	// Manually set the CreateOps.
@@ -84,7 +84,7 @@ func (d *Dir) afterLoad() {
 func (d *Dir) newCreateOps() *ramfs.CreateOps {
 	return &ramfs.CreateOps{
 		NewDir: func(ctx context.Context, dir *fs.Inode, perms fs.FilePermissions) (*fs.Inode, error) {
-			return NewDir(ctx, nil, fs.FileOwnerFromContext(ctx), perms, dir.MountSource, d.platform), nil
+			return NewDir(ctx, nil, fs.FileOwnerFromContext(ctx), perms, dir.MountSource, d.kernel), nil
 		},
 		NewFile: func(ctx context.Context, dir *fs.Inode, perms fs.FilePermissions) (*fs.Inode, error) {
 			uattr := fs.WithCurrentTime(ctx, fs.UnstableAttr{
@@ -93,7 +93,7 @@ func (d *Dir) newCreateOps() *ramfs.CreateOps {
 				// Always start unlinked.
 				Links: 0,
 			})
-			iops := NewInMemoryFile(ctx, usage.Tmpfs, uattr, d.platform)
+			iops := NewInMemoryFile(ctx, usage.Tmpfs, uattr, d.kernel)
 			return fs.NewInode(iops, dir.MountSource, fs.StableAttr{
 				DeviceID:  tmpfsDevice.DeviceID(),
 				InodeID:   tmpfsDevice.NextIno(),

pkg/sentry/kernel/contexttest/BUILD

@@ -0,0 +1,17 @@
+package(licenses = ["notice"])  # Apache 2.0
+
+load("//tools/go_stateify:defs.bzl", "go_library")
+
+go_library(
+    name = "contexttest",
+    testonly = 1,
+    srcs = ["contexttest.go"],
+    importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/kernel/contexttest",
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/sentry/context",
+        "//pkg/sentry/context/contexttest",
+        "//pkg/sentry/kernel",
+        "//pkg/sentry/platform",
+    ],
+)

pkg/sentry/kernel/contexttest/contexttest.go

@@ -0,0 +1,38 @@
+// Copyright 2018 Google LLC
+//
+// 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 contexttest provides a test context.Context which includes
+// a dummy kernel pointing to a valid platform.
+package contexttest
+
+import (
+	"testing"
+
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/context/contexttest"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+)
+
+// Context returns a Context that may be used in tests. Uses ptrace as the
+// platform.Platform, and provides a stub kernel that only serves to point to
+// the platform.
+func Context(tb testing.TB) context.Context {
+	ctx := contexttest.Context(tb)
+	k := &kernel.Kernel{
+		Platform: platform.FromContext(ctx),
+	}
+	ctx.(*contexttest.TestContext).RegisterValue(kernel.CtxKernel, k)
+	return ctx
+}