1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
|
// 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 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.
//
// +stateify savable
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)
}
|
