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// Copyright 2018 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 kernel
import (
"fmt"
"gvisor.dev/gvisor/pkg/safemem"
"gvisor.dev/gvisor/pkg/sentry/memmap"
"gvisor.dev/gvisor/pkg/sentry/pgalloc"
"gvisor.dev/gvisor/pkg/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.
//
// +marshal
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.
//
// +stateify savable
type VDSOParamPage struct {
// The parameter page is fr, allocated from mfp.MemoryFile().
mfp pgalloc.MemoryFileProvider
fr memmap.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
// copyScratchBuffer is a temporary buffer used to marshal the params before
// copying it to the real parameter page. The parameter page is typically
// updated at a moderate frequency of ~O(seconds) throughout the lifetime of
// the sentry, so reusing this buffer is a good tradeoff between memory
// usage and the cost of allocation.
copyScratchBuffer []byte
}
// NewVDSOParamPage returns a VDSOParamPage.
//
// Preconditions:
// * fr is a single page allocated from mfp.MemoryFile(). 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.
// * mfp.MemoryFile().MapInternal(fr) must return a single safemem.Block.
func NewVDSOParamPage(mfp pgalloc.MemoryFileProvider, fr memmap.FileRange) *VDSOParamPage {
return &VDSOParamPage{
mfp: mfp,
fr: fr,
copyScratchBuffer: make([]byte, (*vdsoParams)(nil).SizeBytes()),
}
}
// access returns a mapping of the param page.
func (v *VDSOParamPage) access() (safemem.Block, error) {
bs, err := v.mfp.MemoryFile().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 := v.copyScratchBuffer[:p.SizeBytes()]
p.MarshalUnsafe(buf)
// 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)
}
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