146 lines
4.1 KiB
Go
146 lines
4.1 KiB
Go
// Copyright 2018 Google Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package kernel
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import (
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"fmt"
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"gvisor.googlesource.com/gvisor/pkg/binary"
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"gvisor.googlesource.com/gvisor/pkg/sentry/platform"
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"gvisor.googlesource.com/gvisor/pkg/sentry/safemem"
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"gvisor.googlesource.com/gvisor/pkg/sentry/usermem"
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)
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// vdsoParams are the parameters exposed to the VDSO.
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//
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// They are exposed to the VDSO via a parameter page managed by VDSOParamPage,
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// which also includes a sequence counter.
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type vdsoParams struct {
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monotonicReady uint64
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monotonicBaseCycles int64
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monotonicBaseRef int64
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monotonicFrequency uint64
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realtimeReady uint64
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realtimeBaseCycles int64
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realtimeBaseRef int64
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realtimeFrequency uint64
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}
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// VDSOParamPage manages a VDSO parameter page.
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//
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// Its memory layout looks like:
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//
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// type page struct {
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// // seq is a sequence counter that protects the fields below.
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// seq uint64
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// vdsoParams
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// }
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//
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// Everything in the struct is 8 bytes for easy alignment.
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//
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// It must be kept in sync with params in vdso/vdso_time.cc.
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type VDSOParamPage struct {
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// The parameter page is fr, allocated from platform.Memory().
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platform platform.Platform
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fr platform.FileRange
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// seq is the current sequence count written to the page.
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//
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// A write is in progress if bit 1 of the counter is set.
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//
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// Timekeeper's updater goroutine may call Write before equality is
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// checked in state_test_util tests, causing this field to change across
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// save / restore.
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seq uint64
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}
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// NewVDSOParamPage returns a VDSOParamPage.
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//
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// Preconditions:
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//
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// * fr is a single page allocated from platform.Memory(). VDSOParamPage does
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// not take ownership of fr; it must remain allocated for the lifetime of the
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// VDSOParamPage.
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//
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// * VDSOParamPage must be the only writer to fr.
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//
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// * platform.Memory().MapInternal(fr) must return a single safemem.Block.
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func NewVDSOParamPage(platform platform.Platform, fr platform.FileRange) *VDSOParamPage {
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return &VDSOParamPage{platform: platform, fr: fr}
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}
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// access returns a mapping of the param page.
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func (v *VDSOParamPage) access() (safemem.Block, error) {
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bs, err := v.platform.Memory().MapInternal(v.fr, usermem.ReadWrite)
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if err != nil {
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return safemem.Block{}, err
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}
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if bs.NumBlocks() != 1 {
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panic(fmt.Sprintf("Multiple blocks (%d) in VDSO param BlockSeq", bs.NumBlocks()))
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}
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return bs.Head(), nil
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}
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// incrementSeq increments the sequence counter in the param page.
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func (v *VDSOParamPage) incrementSeq(paramPage safemem.Block) error {
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next := v.seq + 1
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old, err := safemem.SwapUint64(paramPage, next)
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if err != nil {
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return err
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}
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if old != v.seq {
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return fmt.Errorf("unexpected VDSOParamPage seq value: got %d expected %d. Application may hang or get incorrect time from the VDSO.", old, v.seq)
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}
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v.seq = next
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return nil
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}
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// Write updates the VDSO parameters.
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//
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// Write starts a write block, calls f to get the new parameters, writes
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// out the new parameters, then ends the write block.
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func (v *VDSOParamPage) Write(f func() vdsoParams) error {
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paramPage, err := v.access()
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if err != nil {
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return err
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}
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// Write begin.
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next := v.seq + 1
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if next%2 != 1 {
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panic("Out-of-order sequence count")
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}
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err = v.incrementSeq(paramPage)
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if err != nil {
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return err
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}
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// Get the new params.
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p := f()
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buf := binary.Marshal(nil, usermem.ByteOrder, p)
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// Skip the sequence counter.
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if _, err := safemem.Copy(paramPage.DropFirst(8), safemem.BlockFromSafeSlice(buf)); err != nil {
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panic(fmt.Sprintf("Unable to get set VDSO parameters: %v", err))
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}
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// Write end.
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return v.incrementSeq(paramPage)
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}
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