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// Copyright 2021 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 mitigate provides libraries for the mitigate command. The
// mitigate command mitigates side channel attacks such as MDS. Mitigate
// shuts down CPUs via /sys/devices/system/cpu/cpu{N}/online. In addition,
// the mitigate also handles computing available CPU in kubernetes kube_config
// files.
package mitigate
import (
"fmt"
"io/ioutil"
"gvisor.dev/gvisor/pkg/log"
"gvisor.dev/gvisor/runsc/flag"
)
const (
cpuInfo = "/proc/cpuinfo"
allPossibleCPUs = "/sys/devices/system/cpu/possible"
)
// Mitigate handles high level mitigate operations provided to runsc.
type Mitigate struct {
dryRun bool // Run the command without changing the underlying system.
reverse bool // Reverse mitigate by turning on all CPU cores.
other mitigate // Struct holds extra mitigate logic.
path string // path to read for each operation (e.g. /proc/cpuinfo).
}
// Usage implments Usage for cmd.Mitigate.
func (m Mitigate) Usage() string {
usageString := `mitigate [flags]
Mitigate mitigates a system to the "MDS" vulnerability by implementing a manual shutdown of SMT. The command checks /proc/cpuinfo for cpus having the MDS vulnerability, and if found, shutdown all but one CPU per hyperthread pair via /sys/devices/system/cpu/cpu{N}/online. CPUs can be restored by writing "2" to each file in /sys/devices/system/cpu/cpu{N}/online or performing a system reboot.
The command can be reversed with --reverse, which reads the total CPUs from /sys/devices/system/cpu/possible and enables all with /sys/devices/system/cpu/cpu{N}/online.
`
return usageString + m.other.usage()
}
// SetFlags sets flags for the command Mitigate.
func (m Mitigate) SetFlags(f *flag.FlagSet) {
f.BoolVar(&m.dryRun, "dryrun", false, "run the command without changing system")
f.BoolVar(&m.reverse, "reverse", false, "reverse mitigate by enabling all CPUs")
m.other.setFlags(f)
m.path = cpuInfo
if m.reverse {
m.path = allPossibleCPUs
}
}
// Execute executes the Mitigate command.
func (m Mitigate) Execute() error {
data, err := ioutil.ReadFile(m.path)
if err != nil {
return fmt.Errorf("failed to read %s: %v", m.path, err)
}
if m.reverse {
err := m.doReverse(data)
if err != nil {
return fmt.Errorf("reverse operation failed: %v", err)
}
return nil
}
set, err := m.doMitigate(data)
if err != nil {
return fmt.Errorf("mitigate operation failed: %v", err)
}
return m.other.execute(set, m.dryRun)
}
func (m Mitigate) doMitigate(data []byte) (cpuSet, error) {
set, err := newCPUSet(data, m.other.vulnerable)
if err != nil {
return nil, err
}
log.Infof("Mitigate found the following CPUs...")
log.Infof("%s", set)
disableList := set.getShutdownList()
log.Infof("Disabling threads on thread pairs.")
for _, t := range disableList {
log.Infof("Disable thread: %s", t)
if m.dryRun {
continue
}
if err := t.disable(); err != nil {
return nil, fmt.Errorf("error disabling thread: %s err: %v", t, err)
}
}
log.Infof("Shutdown successful.")
return set, nil
}
func (m Mitigate) doReverse(data []byte) error {
set, err := newCPUSetFromPossible(data)
if err != nil {
return err
}
log.Infof("Reverse mitigate found the following CPUs...")
log.Infof("%s", set)
enableList := set.getRemainingList()
log.Infof("Enabling all CPUs...")
for _, t := range enableList {
log.Infof("Enabling thread: %s", t)
if m.dryRun {
continue
}
if err := t.enable(); err != nil {
return fmt.Errorf("error enabling thread: %s err: %v", t, err)
}
}
log.Infof("Enable successful.")
return nil
}
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