1 files changed, 145 insertions, 0 deletions
diff --git a/pkg/sentry/kernel/vdso.go b/pkg/sentry/kernel/vdso.go
new file mode 100644
index 000000000..0bacbea49
--- /dev/null
+++ b/pkg/sentry/kernel/vdso.go
@@ -0,0 +1,145 @@
+// 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 kernel
+
+import (
+	"fmt"
+
+	"gvisor.googlesource.com/gvisor/pkg/binary"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
+)
+
+// vdsoParams are the parameters exposed to the VDSO.
+//
+// They are exposed to the VDSO via a parameter page managed by VDSOParamPage,
+// which also includes a sequence counter.
+type vdsoParams struct {
+	monotonicReady      uint64
+	monotonicBaseCycles int64
+	monotonicBaseRef    int64
+	monotonicFrequency  uint64
+
+	realtimeReady      uint64
+	realtimeBaseCycles int64
+	realtimeBaseRef    int64
+	realtimeFrequency  uint64
+}
+
+// VDSOParamPage manages a VDSO parameter page.
+//
+// Its memory layout looks like:
+//
+// type page struct {
+//	// seq is a sequence counter that protects the fields below.
+//	seq uint64
+//	vdsoParams
+// }
+//
+// Everything in the struct is 8 bytes for easy alignment.
+//
+// It must be kept in sync with params in vdso/vdso_time.cc.
+type VDSOParamPage struct {
+	// The parameter page is fr, allocated from platform.Memory().
+	platform platform.Platform
+	fr       platform.FileRange
+
+	// seq is the current sequence count written to the page.
+	//
+	// A write is in progress if bit 1 of the counter is set.
+	//
+	// Timekeeper's updater goroutine may call Write before equality is
+	// checked in state_test_util tests, causing this field to change across
+	// save / restore.
+	seq uint64
+}
+
+// NewVDSOParamPage returns a VDSOParamPage.
+//
+// Preconditions:
+//
+// * fr is a single page allocated from platform.Memory(). VDSOParamPage does
+//   not take ownership of fr; it must remain allocated for the lifetime of the
+//   VDSOParamPage.
+//
+// * VDSOParamPage must be the only writer to fr.
+//
+// * platform.Memory().MapInternal(fr) must return a single safemem.Block.
+func NewVDSOParamPage(platform platform.Platform, fr platform.FileRange) *VDSOParamPage {
+	return &VDSOParamPage{platform: platform, fr: fr}
+}
+
+// access returns a mapping of the param page.
+func (v *VDSOParamPage) access() (safemem.Block, error) {
+	bs, err := v.platform.Memory().MapInternal(v.fr, usermem.ReadWrite)
+	if err != nil {
+		return safemem.Block{}, err
+	}
+	if bs.NumBlocks() != 1 {
+		panic(fmt.Sprintf("Multiple blocks (%d) in VDSO param BlockSeq", bs.NumBlocks()))
+	}
+	return bs.Head(), nil
+}
+
+// incrementSeq increments the sequence counter in the param page.
+func (v *VDSOParamPage) incrementSeq(paramPage safemem.Block) error {
+	next := v.seq + 1
+	old, err := safemem.SwapUint64(paramPage, next)
+	if err != nil {
+		return err
+	}
+
+	if old != v.seq {
+		return fmt.Errorf("unexpected VDSOParamPage seq value: got %d expected %d. Application may hang or get incorrect time from the VDSO.", old, v.seq)
+	}
+
+	v.seq = next
+	return nil
+}
+
+// Write updates the VDSO parameters.
+//
+// Write starts a write block, calls f to get the new parameters, writes
+// out the new parameters, then ends the write block.
+func (v *VDSOParamPage) Write(f func() vdsoParams) error {
+	paramPage, err := v.access()
+	if err != nil {
+		return err
+	}
+
+	// Write begin.
+	next := v.seq + 1
+	if next%2 != 1 {
+		panic("Out-of-order sequence count")
+	}
+
+	err = v.incrementSeq(paramPage)
+	if err != nil {
+		return err
+	}
+
+	// Get the new params.
+	p := f()
+	buf := binary.Marshal(nil, usermem.ByteOrder, p)
+
+	// Skip the sequence counter.
+	if _, err := safemem.Copy(paramPage.DropFirst(8), safemem.BlockFromSafeSlice(buf)); err != nil {
+		panic(fmt.Sprintf("Unable to get set VDSO parameters: %v", err))
+	}
+
+	// Write end.
+	return v.incrementSeq(paramPage)
+}