Merge release-20210301.0-37-gc5667022b (automated)

21 files changed, 735 insertions, 599 deletions

diff --git a/pkg/sentry/fsimpl/devpts/devpts.go b/pkg/sentry/fsimpl/devpts/devpts.go
index d8c237753..e75954105 100644
--- a/pkg/sentry/fsimpl/devpts/devpts.go
+++ b/pkg/sentry/fsimpl/devpts/devpts.go
@@ -137,6 +137,11 @@ func (fs *filesystem) Release(ctx context.Context) {
 	fs.Filesystem.Release(ctx)
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return ""
+}
+
 // rootInode is the root directory inode for the devpts mounts.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/fuse/fuse_state_autogen.go b/pkg/sentry/fsimpl/fuse/fuse_state_autogen.go
index f59e82755..0a75d80a5 100644
--- a/pkg/sentry/fsimpl/fuse/fuse_state_autogen.go
+++ b/pkg/sentry/fsimpl/fuse/fuse_state_autogen.go
@@ -200,6 +200,7 @@ func (f *filesystemOptions) StateTypeName() string {
 
 func (f *filesystemOptions) StateFields() []string {
 	return []string{
+		"mopts",
 		"userID",
 		"groupID",
 		"rootMode",
@@ -212,21 +213,23 @@ func (f *filesystemOptions) beforeSave() {}
 
 func (f *filesystemOptions) StateSave(stateSinkObject state.Sink) {
 	f.beforeSave()
-	stateSinkObject.Save(0, &f.userID)
-	stateSinkObject.Save(1, &f.groupID)
-	stateSinkObject.Save(2, &f.rootMode)
-	stateSinkObject.Save(3, &f.maxActiveRequests)
-	stateSinkObject.Save(4, &f.maxRead)
+	stateSinkObject.Save(0, &f.mopts)
+	stateSinkObject.Save(1, &f.userID)
+	stateSinkObject.Save(2, &f.groupID)
+	stateSinkObject.Save(3, &f.rootMode)
+	stateSinkObject.Save(4, &f.maxActiveRequests)
+	stateSinkObject.Save(5, &f.maxRead)
 }
 
 func (f *filesystemOptions) afterLoad() {}
 
 func (f *filesystemOptions) StateLoad(stateSourceObject state.Source) {
-	stateSourceObject.Load(0, &f.userID)
-	stateSourceObject.Load(1, &f.groupID)
-	stateSourceObject.Load(2, &f.rootMode)
-	stateSourceObject.Load(3, &f.maxActiveRequests)
-	stateSourceObject.Load(4, &f.maxRead)
+	stateSourceObject.Load(0, &f.mopts)
+	stateSourceObject.Load(1, &f.userID)
+	stateSourceObject.Load(2, &f.groupID)
+	stateSourceObject.Load(3, &f.rootMode)
+	stateSourceObject.Load(4, &f.maxActiveRequests)
+	stateSourceObject.Load(5, &f.maxRead)
 }
 
 func (fs *filesystem) StateTypeName() string {
diff --git a/pkg/sentry/fsimpl/fuse/fusefs.go b/pkg/sentry/fsimpl/fuse/fusefs.go
index 204d8d143..fb0ba2c6d 100644
--- a/pkg/sentry/fsimpl/fuse/fusefs.go
+++ b/pkg/sentry/fsimpl/fuse/fusefs.go
@@ -47,6 +47,9 @@ type FilesystemType struct{}
 
 // +stateify savable
 type filesystemOptions struct {
+	// mopts contains the raw, unparsed mount options passed to this filesystem.
+	mopts string
+
 	// userID specifies the numeric uid of the mount owner.
 	// This option should not be specified by the filesystem owner.
 	// It is set by libfuse (or, if libfuse is not used, must be set
@@ -108,7 +111,7 @@ func (fsType FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		return nil, nil, err
 	}
 
-	var fsopts filesystemOptions
+	fsopts := filesystemOptions{mopts: opts.Data}
 	mopts := vfs.GenericParseMountOptions(opts.Data)
 	deviceDescriptorStr, ok := mopts["fd"]
 	if !ok {
@@ -260,6 +263,11 @@ func (fs *filesystem) Release(ctx context.Context) {
 	fs.Filesystem.Release(ctx)
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return fs.opts.mopts
+}
+
 // inode implements kernfs.Inode.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/gofer/filesystem.go b/pkg/sentry/fsimpl/gofer/filesystem.go
index 8f95473b6..c34451269 100644
--- a/pkg/sentry/fsimpl/gofer/filesystem.go
+++ b/pkg/sentry/fsimpl/gofer/filesystem.go
@@ -15,7 +15,9 @@
 package gofer
 
 import (
+	"fmt"
 	"math"
+	"strings"
 	"sync"
 	"sync/atomic"
 
@@ -1608,3 +1610,58 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 	defer fs.renameMu.RUnlock()
 	return genericPrependPath(vfsroot, vd.Mount(), vd.Dentry().Impl().(*dentry), b)
 }
+
+type mopt struct {
+	key   string
+	value interface{}
+}
+
+func (m mopt) String() string {
+	if m.value == nil {
+		return fmt.Sprintf("%s", m.key)
+	}
+	return fmt.Sprintf("%s=%v", m.key, m.value)
+}
+
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	optsKV := []mopt{
+		{moptTransport, transportModeFD}, // Only valid value, currently.
+		{moptReadFD, fs.opts.fd},         // Currently, read and write FD are the same.
+		{moptWriteFD, fs.opts.fd},        // Currently, read and write FD are the same.
+		{moptAname, fs.opts.aname},
+		{moptDfltUID, fs.opts.dfltuid},
+		{moptDfltGID, fs.opts.dfltgid},
+		{moptMsize, fs.opts.msize},
+		{moptVersion, fs.opts.version},
+		{moptDentryCacheLimit, fs.opts.maxCachedDentries},
+	}
+
+	switch fs.opts.interop {
+	case InteropModeExclusive:
+		optsKV = append(optsKV, mopt{moptCache, cacheFSCache})
+	case InteropModeWritethrough:
+		optsKV = append(optsKV, mopt{moptCache, cacheFSCacheWritethrough})
+	case InteropModeShared:
+		if fs.opts.regularFilesUseSpecialFileFD {
+			optsKV = append(optsKV, mopt{moptCache, cacheNone})
+		} else {
+			optsKV = append(optsKV, mopt{moptCache, cacheRemoteRevalidating})
+		}
+	}
+	if fs.opts.forcePageCache {
+		optsKV = append(optsKV, mopt{moptForcePageCache, nil})
+	}
+	if fs.opts.limitHostFDTranslation {
+		optsKV = append(optsKV, mopt{moptLimitHostFDTranslation, nil})
+	}
+	if fs.opts.overlayfsStaleRead {
+		optsKV = append(optsKV, mopt{moptOverlayfsStaleRead, nil})
+	}
+
+	opts := make([]string, 0, len(optsKV))
+	for _, opt := range optsKV {
+		opts = append(opts, opt.String())
+	}
+	return strings.Join(opts, ",")
+}
diff --git a/pkg/sentry/fsimpl/gofer/gofer.go b/pkg/sentry/fsimpl/gofer/gofer.go
index 1508cbdf1..71569dc65 100644
--- a/pkg/sentry/fsimpl/gofer/gofer.go
+++ b/pkg/sentry/fsimpl/gofer/gofer.go
@@ -66,6 +66,34 @@ import (
 // Name is the default filesystem name.
 const Name = "9p"
 
+// Mount option names for goferfs.
+const (
+	moptTransport              = "trans"
+	moptReadFD                 = "rfdno"
+	moptWriteFD                = "wfdno"
+	moptAname                  = "aname"
+	moptDfltUID                = "dfltuid"
+	moptDfltGID                = "dfltgid"
+	moptMsize                  = "msize"
+	moptVersion                = "version"
+	moptDentryCacheLimit       = "dentry_cache_limit"
+	moptCache                  = "cache"
+	moptForcePageCache         = "force_page_cache"
+	moptLimitHostFDTranslation = "limit_host_fd_translation"
+	moptOverlayfsStaleRead     = "overlayfs_stale_read"
+)
+
+// Valid values for the "cache" mount option.
+const (
+	cacheNone                = "none"
+	cacheFSCache             = "fscache"
+	cacheFSCacheWritethrough = "fscache_writethrough"
+	cacheRemoteRevalidating  = "remote_revalidating"
+)
+
+// Valid values for "trans" mount option.
+const transportModeFD = "fd"
+
 // FilesystemType implements vfs.FilesystemType.
 //
 // +stateify savable
@@ -301,39 +329,39 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 
 	// Get the attach name.
 	fsopts.aname = "/"
-	if aname, ok := mopts["aname"]; ok {
-		delete(mopts, "aname")
+	if aname, ok := mopts[moptAname]; ok {
+		delete(mopts, moptAname)
 		fsopts.aname = aname
 	}
 
 	// Parse the cache policy. For historical reasons, this defaults to the
 	// least generally-applicable option, InteropModeExclusive.
 	fsopts.interop = InteropModeExclusive
-	if cache, ok := mopts["cache"]; ok {
-		delete(mopts, "cache")
+	if cache, ok := mopts[moptCache]; ok {
+		delete(mopts, moptCache)
 		switch cache {
-		case "fscache":
+		case cacheFSCache:
 			fsopts.interop = InteropModeExclusive
-		case "fscache_writethrough":
+		case cacheFSCacheWritethrough:
 			fsopts.interop = InteropModeWritethrough
-		case "none":
+		case cacheNone:
 			fsopts.regularFilesUseSpecialFileFD = true
 			fallthrough
-		case "remote_revalidating":
+		case cacheRemoteRevalidating:
 			fsopts.interop = InteropModeShared
 		default:
-			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid cache policy: cache=%s", cache)
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid cache policy: %s=%s", moptCache, cache)
 			return nil, nil, syserror.EINVAL
 		}
 	}
 
 	// Parse the default UID and GID.
 	fsopts.dfltuid = _V9FS_DEFUID
-	if dfltuidstr, ok := mopts["dfltuid"]; ok {
-		delete(mopts, "dfltuid")
+	if dfltuidstr, ok := mopts[moptDfltUID]; ok {
+		delete(mopts, moptDfltUID)
 		dfltuid, err := strconv.ParseUint(dfltuidstr, 10, 32)
 		if err != nil {
-			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid default UID: dfltuid=%s", dfltuidstr)
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid default UID: %s=%s", moptDfltUID, dfltuidstr)
 			return nil, nil, syserror.EINVAL
 		}
 		// In Linux, dfltuid is interpreted as a UID and is converted to a KUID
@@ -342,11 +370,11 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		fsopts.dfltuid = auth.KUID(dfltuid)
 	}
 	fsopts.dfltgid = _V9FS_DEFGID
-	if dfltgidstr, ok := mopts["dfltgid"]; ok {
-		delete(mopts, "dfltgid")
+	if dfltgidstr, ok := mopts[moptDfltGID]; ok {
+		delete(mopts, moptDfltGID)
 		dfltgid, err := strconv.ParseUint(dfltgidstr, 10, 32)
 		if err != nil {
-			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid default UID: dfltgid=%s", dfltgidstr)
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid default UID: %s=%s", moptDfltGID, dfltgidstr)
 			return nil, nil, syserror.EINVAL
 		}
 		fsopts.dfltgid = auth.KGID(dfltgid)
@@ -354,11 +382,11 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 
 	// Parse the 9P message size.
 	fsopts.msize = 1024 * 1024 // 1M, tested to give good enough performance up to 64M
-	if msizestr, ok := mopts["msize"]; ok {
-		delete(mopts, "msize")
+	if msizestr, ok := mopts[moptMsize]; ok {
+		delete(mopts, moptMsize)
 		msize, err := strconv.ParseUint(msizestr, 10, 32)
 		if err != nil {
-			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid message size: msize=%s", msizestr)
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid message size: %s=%s", moptMsize, msizestr)
 			return nil, nil, syserror.EINVAL
 		}
 		fsopts.msize = uint32(msize)
@@ -366,34 +394,34 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 
 	// Parse the 9P protocol version.
 	fsopts.version = p9.HighestVersionString()
-	if version, ok := mopts["version"]; ok {
-		delete(mopts, "version")
+	if version, ok := mopts[moptVersion]; ok {
+		delete(mopts, moptVersion)
 		fsopts.version = version
 	}
 
 	// Parse the dentry cache limit.
 	fsopts.maxCachedDentries = 1000
-	if str, ok := mopts["dentry_cache_limit"]; ok {
-		delete(mopts, "dentry_cache_limit")
+	if str, ok := mopts[moptDentryCacheLimit]; ok {
+		delete(mopts, moptDentryCacheLimit)
 		maxCachedDentries, err := strconv.ParseUint(str, 10, 64)
 		if err != nil {
-			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid dentry cache limit: dentry_cache_limit=%s", str)
+			ctx.Warningf("gofer.FilesystemType.GetFilesystem: invalid dentry cache limit: %s=%s", moptDentryCacheLimit, str)
 			return nil, nil, syserror.EINVAL
 		}
 		fsopts.maxCachedDentries = maxCachedDentries
 	}
 
 	// Handle simple flags.
-	if _, ok := mopts["force_page_cache"]; ok {
-		delete(mopts, "force_page_cache")
+	if _, ok := mopts[moptForcePageCache]; ok {
+		delete(mopts, moptForcePageCache)
 		fsopts.forcePageCache = true
 	}
-	if _, ok := mopts["limit_host_fd_translation"]; ok {
-		delete(mopts, "limit_host_fd_translation")
+	if _, ok := mopts[moptLimitHostFDTranslation]; ok {
+		delete(mopts, moptLimitHostFDTranslation)
 		fsopts.limitHostFDTranslation = true
 	}
-	if _, ok := mopts["overlayfs_stale_read"]; ok {
-		delete(mopts, "overlayfs_stale_read")
+	if _, ok := mopts[moptOverlayfsStaleRead]; ok {
+		delete(mopts, moptOverlayfsStaleRead)
 		fsopts.overlayfsStaleRead = true
 	}
 	// fsopts.regularFilesUseSpecialFileFD can only be enabled by specifying
@@ -469,34 +497,34 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 
 func getFDFromMountOptionsMap(ctx context.Context, mopts map[string]string) (int, error) {
 	// Check that the transport is "fd".
-	trans, ok := mopts["trans"]
-	if !ok || trans != "fd" {
-		ctx.Warningf("gofer.getFDFromMountOptionsMap: transport must be specified as 'trans=fd'")
+	trans, ok := mopts[moptTransport]
+	if !ok || trans != transportModeFD {
+		ctx.Warningf("gofer.getFDFromMountOptionsMap: transport must be specified as '%s=%s'", moptTransport, transportModeFD)
 		return -1, syserror.EINVAL
 	}
-	delete(mopts, "trans")
+	delete(mopts, moptTransport)
 
 	// Check that read and write FDs are provided and identical.
-	rfdstr, ok := mopts["rfdno"]
+	rfdstr, ok := mopts[moptReadFD]
 	if !ok {
-		ctx.Warningf("gofer.getFDFromMountOptionsMap: read FD must be specified as 'rfdno=<file descriptor>'")
+		ctx.Warningf("gofer.getFDFromMountOptionsMap: read FD must be specified as '%s=<file descriptor>'", moptReadFD)
 		return -1, syserror.EINVAL
 	}
-	delete(mopts, "rfdno")
+	delete(mopts, moptReadFD)
 	rfd, err := strconv.Atoi(rfdstr)
 	if err != nil {
-		ctx.Warningf("gofer.getFDFromMountOptionsMap: invalid read FD: rfdno=%s", rfdstr)
+		ctx.Warningf("gofer.getFDFromMountOptionsMap: invalid read FD: %s=%s", moptReadFD, rfdstr)
 		return -1, syserror.EINVAL
 	}
-	wfdstr, ok := mopts["wfdno"]
+	wfdstr, ok := mopts[moptWriteFD]
 	if !ok {
-		ctx.Warningf("gofer.getFDFromMountOptionsMap: write FD must be specified as 'wfdno=<file descriptor>'")
+		ctx.Warningf("gofer.getFDFromMountOptionsMap: write FD must be specified as '%s=<file descriptor>'", moptWriteFD)
 		return -1, syserror.EINVAL
 	}
-	delete(mopts, "wfdno")
+	delete(mopts, moptWriteFD)
 	wfd, err := strconv.Atoi(wfdstr)
 	if err != nil {
-		ctx.Warningf("gofer.getFDFromMountOptionsMap: invalid write FD: wfdno=%s", wfdstr)
+		ctx.Warningf("gofer.getFDFromMountOptionsMap: invalid write FD: %s=%s", moptWriteFD, wfdstr)
 		return -1, syserror.EINVAL
 	}
 	if rfd != wfd {
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index ad5de80dc..b9cce4181 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -260,6 +260,11 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 	return vfs.PrependPathSyntheticError{}
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return ""
+}
+
 // CheckPermissions implements kernfs.Inode.CheckPermissions.
 func (i *inode) CheckPermissions(ctx context.Context, creds *auth.Credentials, ats vfs.AccessTypes) error {
 	var s unix.Stat_t
diff --git a/pkg/sentry/fsimpl/overlay/filesystem.go b/pkg/sentry/fsimpl/overlay/filesystem.go
index 917709d75..84e37f793 100644
--- a/pkg/sentry/fsimpl/overlay/filesystem.go
+++ b/pkg/sentry/fsimpl/overlay/filesystem.go
@@ -1764,3 +1764,15 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 	defer fs.renameMu.RUnlock()
 	return genericPrependPath(vfsroot, vd.Mount(), vd.Dentry().Impl().(*dentry), b)
 }
+
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	// Return the mount options from the topmost layer.
+	var vd vfs.VirtualDentry
+	if fs.opts.UpperRoot.Ok() {
+		vd = fs.opts.UpperRoot
+	} else {
+		vd = fs.opts.LowerRoots[0]
+	}
+	return vd.Mount().Filesystem().Impl().MountOptions()
+}
diff --git a/pkg/sentry/fsimpl/pipefs/pipefs.go b/pkg/sentry/fsimpl/pipefs/pipefs.go
index 429733c10..3f05e444e 100644
--- a/pkg/sentry/fsimpl/pipefs/pipefs.go
+++ b/pkg/sentry/fsimpl/pipefs/pipefs.go
@@ -80,6 +80,11 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 	return vfs.PrependPathSyntheticError{}
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return ""
+}
+
 // inode implements kernfs.Inode.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/proc/filesystem.go b/pkg/sentry/fsimpl/proc/filesystem.go
index 8716d0a3c..254a8b062 100644
--- a/pkg/sentry/fsimpl/proc/filesystem.go
+++ b/pkg/sentry/fsimpl/proc/filesystem.go
@@ -104,6 +104,11 @@ func (fs *filesystem) Release(ctx context.Context) {
 	fs.Filesystem.Release(ctx)
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return fmt.Sprintf("dentry_cache_limit=%d", fs.MaxCachedDentries)
+}
+
 // dynamicInode is an overfitted interface for common Inodes with
 // dynamicByteSource types used in procfs.
 //
diff --git a/pkg/sentry/fsimpl/sockfs/sockfs.go b/pkg/sentry/fsimpl/sockfs/sockfs.go
index fda1fa942..735756280 100644
--- a/pkg/sentry/fsimpl/sockfs/sockfs.go
+++ b/pkg/sentry/fsimpl/sockfs/sockfs.go
@@ -85,6 +85,11 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 	return vfs.PrependPathSyntheticError{}
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return ""
+}
+
 // inode implements kernfs.Inode.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/sys/sys.go b/pkg/sentry/fsimpl/sys/sys.go
index dbd9ebdda..1d9280dae 100644
--- a/pkg/sentry/fsimpl/sys/sys.go
+++ b/pkg/sentry/fsimpl/sys/sys.go
@@ -143,6 +143,11 @@ func (fs *filesystem) Release(ctx context.Context) {
 	fs.Filesystem.Release(ctx)
 }
 
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return fmt.Sprintf("dentry_cache_limit=%d", fs.MaxCachedDentries)
+}
+
 // dir implements kernfs.Inode.
 //
 // +stateify savable
diff --git a/pkg/sentry/fsimpl/tmpfs/filesystem.go b/pkg/sentry/fsimpl/tmpfs/filesystem.go
index 4f675c21e..5fdca1d46 100644
--- a/pkg/sentry/fsimpl/tmpfs/filesystem.go
+++ b/pkg/sentry/fsimpl/tmpfs/filesystem.go
@@ -898,3 +898,8 @@ func (fs *filesystem) PrependPath(ctx context.Context, vfsroot, vd vfs.VirtualDe
 		d = d.parent
 	}
 }
+
+// MountOptions implements vfs.FilesystemImpl.MountOptions.
+func (fs *filesystem) MountOptions() string {
+	return fs.mopts
+}
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs.go b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
index a01e413e0..8df81f589 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs.go
@@ -70,6 +70,10 @@ type filesystem struct {
 	// devMinor is the filesystem's minor device number. devMinor is immutable.
 	devMinor uint32
 
+	// mopts contains the tmpfs-specific mount options passed to this
+	// filesystem. Immutable.
+	mopts string
+
 	// mu serializes changes to the Dentry tree.
 	mu sync.RWMutex `state:"nosave"`
 
@@ -184,6 +188,7 @@ func (fstype FilesystemType) GetFilesystem(ctx context.Context, vfsObj *vfs.Virt
 		mfp:      mfp,
 		clock:    clock,
 		devMinor: devMinor,
+		mopts:    opts.Data,
 	}
 	fs.vfsfs.Init(vfsObj, newFSType, &fs)
 
diff --git a/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go b/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
index 21c53afaf..bd0b0bf97 100644
--- a/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
+++ b/pkg/sentry/fsimpl/tmpfs/tmpfs_state_autogen.go
@@ -352,6 +352,7 @@ func (fs *filesystem) StateFields() []string {
 		"mfp",
 		"clock",
 		"devMinor",
+		"mopts",
 		"nextInoMinusOne",
 		"root",
 	}
@@ -365,8 +366,9 @@ func (fs *filesystem) StateSave(stateSinkObject state.Sink) {
 	stateSinkObject.Save(1, &fs.mfp)
 	stateSinkObject.Save(2, &fs.clock)
 	stateSinkObject.Save(3, &fs.devMinor)
-	stateSinkObject.Save(4, &fs.nextInoMinusOne)
-	stateSinkObject.Save(5, &fs.root)
+	stateSinkObject.Save(4, &fs.mopts)
+	stateSinkObject.Save(5, &fs.nextInoMinusOne)
+	stateSinkObject.Save(6, &fs.root)
 }
 
 func (fs *filesystem) afterLoad() {}
@@ -376,8 +378,9 @@ func (fs *filesystem) StateLoad(stateSourceObject state.Source) {
 	stateSourceObject.Load(1, &fs.mfp)
 	stateSourceObject.Load(2, &fs.clock)
 	stateSourceObject.Load(3, &fs.devMinor)
-	stateSourceObject.Load(4, &fs.nextInoMinusOne)
-	stateSourceObject.Load(5, &fs.root)
+	stateSourceObject.Load(4, &fs.mopts)
+	stateSourceObject.Load(5, &fs.nextInoMinusOne)
+	stateSourceObject.Load(6, &fs.root)
 }
 
 func (f *FilesystemOpts) StateTypeName() string {
diff --git a/pkg/sentry/vfs/anonfs.go b/pkg/sentry/vfs/anonfs.go
index 7ad0eaf86..3caf417ca 100644
--- a/pkg/sentry/vfs/anonfs.go
+++ b/pkg/sentry/vfs/anonfs.go
@@ -291,6 +291,11 @@ func (fs *anonFilesystem) PrependPath(ctx context.Context, vfsroot, vd VirtualDe
 	return PrependPathSyntheticError{}
 }
 
+// MountOptions implements FilesystemImpl.MountOptions.
+func (fs *anonFilesystem) MountOptions() string {
+	return ""
+}
+
 // IncRef implements DentryImpl.IncRef.
 func (d *anonDentry) IncRef() {
 	// no-op
diff --git a/pkg/sentry/vfs/filesystem.go b/pkg/sentry/vfs/filesystem.go
index 2c4b81e78..059939010 100644
--- a/pkg/sentry/vfs/filesystem.go
+++ b/pkg/sentry/vfs/filesystem.go
@@ -502,6 +502,15 @@ type FilesystemImpl interface {
 	//
 	// Preconditions: vd.Mount().Filesystem().Impl() == this FilesystemImpl.
 	PrependPath(ctx context.Context, vfsroot, vd VirtualDentry, b *fspath.Builder) error
+
+	// MountOptions returns mount options for the current filesystem. This
+	// should only return options specific to the filesystem (i.e. don't return
+	// "ro", "rw", etc). Options should be returned as a comma-separated string,
+	// similar to the input to the 5th argument to mount.
+	//
+	// If the implementation has no filesystem-specific options, it should
+	// return the empty string.
+	MountOptions() string
 }
 
 // PrependPathAtVFSRootError is returned by implementations of
diff --git a/pkg/sentry/vfs/mount.go b/pkg/sentry/vfs/mount.go
index bac9eb905..922f9e697 100644
--- a/pkg/sentry/vfs/mount.go
+++ b/pkg/sentry/vfs/mount.go
@@ -959,13 +959,17 @@ func manglePath(p string) string {
 // superBlockOpts returns the super block options string for the the mount at
 // the given path.
 func superBlockOpts(mountPath string, mnt *Mount) string {
-	// gVisor doesn't (yet) have a concept of super block options, so we
-	// use the ro/rw bit from the mount flag.
+	// Compose super block options by combining global mount flags with
+	// FS-specific mount options.
 	opts := "rw"
 	if mnt.ReadOnly() {
 		opts = "ro"
 	}
 
+	if mopts := mnt.fs.Impl().MountOptions(); mopts != "" {
+		opts += "," + mopts
+	}
+
 	// NOTE(b/147673608): If the mount is a cgroup, we also need to include
 	// the cgroup name in the options. For now we just read that from the
 	// path.
diff --git a/runsc/cmd/mitigate.go b/runsc/cmd/mitigate.go
index 822af1917..fddf0e0dd 100644
--- a/runsc/cmd/mitigate.go
+++ b/runsc/cmd/mitigate.go
@@ -16,6 +16,8 @@ package cmd
 
 import (
 	"context"
+	"fmt"
+	"io/ioutil"
 
 	"github.com/google/subcommands"
 	"gvisor.dev/gvisor/pkg/log"
@@ -23,9 +25,23 @@ import (
 	"gvisor.dev/gvisor/runsc/mitigate"
 )
 
+const (
+	// cpuInfo is the path used to parse CPU info.
+	cpuInfo = "/proc/cpuinfo"
+	// allPossibleCPUs is the path used to enable CPUs.
+	allPossibleCPUs = "/sys/devices/system/cpu/possible"
+)
+
 // Mitigate implements subcommands.Command for the "mitigate" command.
 type Mitigate struct {
-	mitigate mitigate.Mitigate
+	// Run the command without changing the underlying system.
+	dryRun bool
+	// Reverse mitigate by turning on all CPU cores.
+	reverse bool
+	// Path to file to read to create CPUSet.
+	path string
+	// Callback to check if a given thread is vulnerable.
+	vulnerable func(other mitigate.Thread) bool
 }
 
 // Name implements subcommands.command.name.
@@ -38,14 +54,19 @@ func (*Mitigate) Synopsis() string {
 	return "mitigate mitigates the underlying system against side channel attacks"
 }
 
-// Usage implements subcommands.Command.Usage.
-func (m *Mitigate) Usage() string {
-	return m.mitigate.Usage()
+// Usage implments Usage for cmd.Mitigate.
+func (m Mitigate) Usage() string {
+	return `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.`
 }
 
-// SetFlags implements subcommands.Command.SetFlags.
+// SetFlags sets flags for the command Mitigate.
 func (m *Mitigate) SetFlags(f *flag.FlagSet) {
-	m.mitigate.SetFlags(f)
+	f.BoolVar(&m.dryRun, "dryrun", false, "run the command without changing system")
+	f.BoolVar(&m.reverse, "reverse", false, "reverse mitigate by enabling all CPUs")
 }
 
 // Execute implements subcommands.Command.Execute.
@@ -55,10 +76,97 @@ func (m *Mitigate) Execute(_ context.Context, f *flag.FlagSet, args ...interface
 		return subcommands.ExitUsageError
 	}
 
-	if err := m.mitigate.Execute(); err != nil {
+	m.path = cpuInfo
+	if m.reverse {
+		m.path = allPossibleCPUs
+	}
+
+	m.vulnerable = func(other mitigate.Thread) bool {
+		return other.IsVulnerable()
+	}
+
+	if _, err := m.doExecute(); err != nil {
 		log.Warningf("Execute failed: %v", err)
 		return subcommands.ExitFailure
 	}
 
 	return subcommands.ExitSuccess
 }
+
+// Execute executes the Mitigate command.
+func (m *Mitigate) doExecute() (mitigate.CPUSet, error) {
+	if m.dryRun {
+		log.Infof("Running with DryRun. No cpu settings will be changed.")
+	}
+	if m.reverse {
+		data, err := ioutil.ReadFile(m.path)
+		if err != nil {
+			return nil, fmt.Errorf("failed to read %s: %v", m.path, err)
+		}
+
+		set, err := m.doReverse(data)
+		if err != nil {
+			return nil, fmt.Errorf("reverse operation failed: %v", err)
+		}
+		return set, nil
+	}
+
+	data, err := ioutil.ReadFile(m.path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read %s: %v", m.path, err)
+	}
+	set, err := m.doMitigate(data)
+	if err != nil {
+		return nil, fmt.Errorf("mitigate operation failed: %v", err)
+	}
+	return set, nil
+}
+
+func (m *Mitigate) doMitigate(data []byte) (mitigate.CPUSet, error) {
+	set, err := mitigate.NewCPUSet(data, m.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) (mitigate.CPUSet, error) {
+	set, err := mitigate.NewCPUSetFromPossible(data)
+	if err != nil {
+		return nil, 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 nil, fmt.Errorf("error enabling thread: %s err: %v", t, err)
+		}
+	}
+	log.Infof("Enable successful.")
+	return set, nil
+}
diff --git a/runsc/mitigate/cpu.go b/runsc/mitigate/cpu.go
deleted file mode 100644
index 4b2aa351f..000000000
--- a/runsc/mitigate/cpu.go
+++ /dev/null
@@ -1,423 +0,0 @@
-// 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
-
-import (
-	"fmt"
-	"io/ioutil"
-	"regexp"
-	"strconv"
-	"strings"
-)
-
-const (
-	// mds is the only bug we care about.
-	mds = "mds"
-
-	// Constants for parsing /proc/cpuinfo.
-	processorKey  = "processor"
-	vendorIDKey   = "vendor_id"
-	cpuFamilyKey  = "cpu family"
-	modelKey      = "model"
-	physicalIDKey = "physical id"
-	coreIDKey     = "core id"
-	bugsKey       = "bugs"
-
-	// Path to shutdown a CPU.
-	cpuOnlineTemplate = "/sys/devices/system/cpu/cpu%d/online"
-)
-
-// cpuSet contains a map of all CPUs on the system, mapped
-// by Physical ID and CoreIDs. threads with the same
-// Core and Physical ID are Hyperthread pairs.
-type cpuSet map[cpuID]*threadGroup
-
-// newCPUSet creates a CPUSet from data read from /proc/cpuinfo.
-func newCPUSet(data []byte, vulnerable func(thread) bool) (cpuSet, error) {
-	processors, err := getThreads(string(data))
-	if err != nil {
-		return nil, err
-	}
-
-	set := make(cpuSet)
-	for _, p := range processors {
-		// Each ID is of the form physicalID:coreID. Hyperthread pairs
-		// have identical physical and core IDs. We need to match
-		// Hyperthread pairs so that we can shutdown all but one per
-		// pair.
-		core, ok := set[p.id]
-		if !ok {
-			core = &threadGroup{}
-			set[p.id] = core
-		}
-		core.isVulnerable = core.isVulnerable || vulnerable(p)
-		core.threads = append(core.threads, p)
-	}
-	return set, nil
-}
-
-// newCPUSetFromPossible makes a cpuSet data read from
-// /sys/devices/system/cpu/possible. This is used in enable operations
-// where the caller simply wants to enable all CPUS.
-func newCPUSetFromPossible(data []byte) (cpuSet, error) {
-	threads, err := getThreadsFromPossible(data)
-	if err != nil {
-		return nil, err
-	}
-
-	// We don't care if a CPU is vulnerable or not, we just
-	// want to return a list of all CPUs on the host.
-	set := cpuSet{
-		threads[0].id: &threadGroup{
-			threads:      threads,
-			isVulnerable: false,
-		},
-	}
-	return set, nil
-}
-
-// String implements the String method for CPUSet.
-func (c cpuSet) String() string {
-	ret := ""
-	for _, tg := range c {
-		ret += fmt.Sprintf("%s\n", tg)
-	}
-	return ret
-}
-
-// getRemainingList returns the list of threads that will remain active
-// after mitigation.
-func (c cpuSet) getRemainingList() []thread {
-	threads := make([]thread, 0, len(c))
-	for _, core := range c {
-		// If we're vulnerable, take only one thread from the pair.
-		if core.isVulnerable {
-			threads = append(threads, core.threads[0])
-			continue
-		}
-		// Otherwise don't shutdown anything.
-		threads = append(threads, core.threads...)
-	}
-	return threads
-}
-
-// getShutdownList returns the list of threads that will be shutdown on
-// mitigation.
-func (c cpuSet) getShutdownList() []thread {
-	threads := make([]thread, 0)
-	for _, core := range c {
-		// Only if we're vulnerable do shutdown anything. In this case,
-		// shutdown all but the first entry.
-		if core.isVulnerable && len(core.threads) > 1 {
-			threads = append(threads, core.threads[1:]...)
-		}
-	}
-	return threads
-}
-
-// threadGroup represents Hyperthread pairs on the same physical/core ID.
-type threadGroup struct {
-	threads      []thread
-	isVulnerable bool
-}
-
-// String implements the String method for threadGroup.
-func (c threadGroup) String() string {
-	ret := fmt.Sprintf("ThreadGroup:\nIsVulnerable: %t\n", c.isVulnerable)
-	for _, processor := range c.threads {
-		ret += fmt.Sprintf("%s\n", processor)
-	}
-	return ret
-}
-
-// getThreads returns threads structs from reading /proc/cpuinfo.
-func getThreads(data string) ([]thread, error) {
-	// Each processor entry should start with the
-	// processor key. Find the beginings of each.
-	r := buildRegex(processorKey, `\d+`)
-	indices := r.FindAllStringIndex(data, -1)
-	if len(indices) < 1 {
-		return nil, fmt.Errorf("no cpus found for: %q", data)
-	}
-
-	// Add the ending index for last entry.
-	indices = append(indices, []int{len(data), -1})
-
-	// Valid cpus are now defined by strings in between
-	// indexes (e.g. data[index[i], index[i+1]]).
-	// There should be len(indicies) - 1 CPUs
-	// since the last index is the end of the string.
-	cpus := make([]thread, 0, len(indices))
-	// Find each string that represents a CPU. These begin "processor".
-	for i := 1; i < len(indices); i++ {
-		start := indices[i-1][0]
-		end := indices[i][0]
-		// Parse the CPU entry, which should be between start/end.
-		c, err := newThread(data[start:end])
-		if err != nil {
-			return nil, err
-		}
-		cpus = append(cpus, c)
-	}
-	return cpus, nil
-}
-
-// getThreadsFromPossible makes threads from data read from /sys/devices/system/cpu/possible.
-func getThreadsFromPossible(data []byte) ([]thread, error) {
-	possibleRegex := regexp.MustCompile(`(?m)^(\d+)(-(\d+))?$`)
-	matches := possibleRegex.FindStringSubmatch(string(data))
-	if len(matches) != 4 {
-		return nil, fmt.Errorf("mismatch regex from %s: %q", allPossibleCPUs, string(data))
-	}
-
-	// If matches[3] is empty, we only have one cpu entry.
-	if matches[3] == "" {
-		matches[3] = matches[1]
-	}
-
-	begin, err := strconv.ParseInt(matches[1], 10, 64)
-	if err != nil {
-		return nil, fmt.Errorf("failed to parse begin: %v", err)
-	}
-	end, err := strconv.ParseInt(matches[3], 10, 64)
-	if err != nil {
-		return nil, fmt.Errorf("failed to parse end: %v", err)
-	}
-	if begin > end || begin < 0 || end < 0 {
-		return nil, fmt.Errorf("invalid cpu bounds from possible: begin: %d end: %d", begin, end)
-	}
-
-	ret := make([]thread, 0, end-begin)
-	for i := begin; i <= end; i++ {
-		ret = append(ret, thread{
-			processorNumber: i,
-			id: cpuID{
-				physicalID: 0, // we don't care about id for enable ops.
-				coreID:     0,
-			},
-		})
-	}
-
-	return ret, nil
-}
-
-// cpuID for each thread is defined by the physical and
-// core IDs. If equal, two threads are Hyperthread pairs.
-type cpuID struct {
-	physicalID int64
-	coreID     int64
-}
-
-// type cpu represents pertinent info about a cpu.
-type thread struct {
-	processorNumber int64               // the processor number of this CPU.
-	vendorID        string              // the vendorID of CPU (e.g. AuthenticAMD).
-	cpuFamily       int64               // CPU family number (e.g. 6 for CascadeLake/Skylake).
-	model           int64               // CPU model number (e.g. 85 for CascadeLake/Skylake).
-	id              cpuID               // id for this thread
-	bugs            map[string]struct{} // map of vulnerabilities parsed from the 'bugs' field.
-}
-
-// newThread parses a CPU from a single cpu entry from /proc/cpuinfo.
-func newThread(data string) (thread, error) {
-	empty := thread{}
-	processor, err := parseProcessor(data)
-	if err != nil {
-		return empty, err
-	}
-
-	vendorID, err := parseVendorID(data)
-	if err != nil {
-		return empty, err
-	}
-
-	cpuFamily, err := parseCPUFamily(data)
-	if err != nil {
-		return empty, err
-	}
-
-	model, err := parseModel(data)
-	if err != nil {
-		return empty, err
-	}
-
-	physicalID, err := parsePhysicalID(data)
-	if err != nil {
-		return empty, err
-	}
-
-	coreID, err := parseCoreID(data)
-	if err != nil {
-		return empty, err
-	}
-
-	bugs, err := parseBugs(data)
-	if err != nil {
-		return empty, err
-	}
-
-	return thread{
-		processorNumber: processor,
-		vendorID:        vendorID,
-		cpuFamily:       cpuFamily,
-		model:           model,
-		id: cpuID{
-			physicalID: physicalID,
-			coreID:     coreID,
-		},
-		bugs: bugs,
-	}, nil
-}
-
-// String implements the String method for thread.
-func (t thread) String() string {
-	template := `CPU: %d
-CPU ID: %+v
-Vendor: %s
-Family/Model: %d/%d
-Bugs: %s
-`
-	bugs := make([]string, 0)
-	for bug := range t.bugs {
-		bugs = append(bugs, bug)
-	}
-
-	return fmt.Sprintf(template, t.processorNumber, t.id, t.vendorID, t.cpuFamily, t.model, strings.Join(bugs, ","))
-}
-
-// enable turns on the CPU by writing 1 to /sys/devices/cpu/cpu{N}/online.
-func (t thread) enable() error {
-	cpuPath := fmt.Sprintf(cpuOnlineTemplate, t.processorNumber)
-	return ioutil.WriteFile(cpuPath, []byte{'1'}, 0644)
-}
-
-// disable turns off the CPU by writing 0 to /sys/devices/cpu/cpu{N}/online.
-func (t thread) disable() error {
-	cpuPath := fmt.Sprintf(cpuOnlineTemplate, t.processorNumber)
-	return ioutil.WriteFile(cpuPath, []byte{'0'}, 0644)
-}
-
-// isVulnerable checks if a CPU is vulnerable to mds.
-func (t thread) isVulnerable() bool {
-	_, ok := t.bugs[mds]
-	return ok
-}
-
-// isActive checks if a CPU is active from /sys/devices/system/cpu/cpu{N}/online
-// If the file does not exist (ioutil returns in error), we assume the CPU is on.
-func (t thread) isActive() bool {
-	cpuPath := fmt.Sprintf(cpuOnlineTemplate, t.processorNumber)
-	data, err := ioutil.ReadFile(cpuPath)
-	if err != nil {
-		return true
-	}
-	return len(data) > 0 && data[0] != '0'
-}
-
-// similarTo checks family/model/bugs fields for equality of two
-// processors.
-func (t thread) similarTo(other thread) bool {
-	if t.vendorID != other.vendorID {
-		return false
-	}
-
-	if other.cpuFamily != t.cpuFamily {
-		return false
-	}
-
-	if other.model != t.model {
-		return false
-	}
-
-	if len(other.bugs) != len(t.bugs) {
-		return false
-	}
-
-	for bug := range t.bugs {
-		if _, ok := other.bugs[bug]; !ok {
-			return false
-		}
-	}
-	return true
-}
-
-// parseProcessor grabs the processor field from /proc/cpuinfo output.
-func parseProcessor(data string) (int64, error) {
-	return parseIntegerResult(data, processorKey)
-}
-
-// parseVendorID grabs the vendor_id field from /proc/cpuinfo output.
-func parseVendorID(data string) (string, error) {
-	return parseRegex(data, vendorIDKey, `[\w\d]+`)
-}
-
-// parseCPUFamily grabs the cpu family field from /proc/cpuinfo output.
-func parseCPUFamily(data string) (int64, error) {
-	return parseIntegerResult(data, cpuFamilyKey)
-}
-
-// parseModel grabs the model field from /proc/cpuinfo output.
-func parseModel(data string) (int64, error) {
-	return parseIntegerResult(data, modelKey)
-}
-
-// parsePhysicalID parses the physical id field.
-func parsePhysicalID(data string) (int64, error) {
-	return parseIntegerResult(data, physicalIDKey)
-}
-
-// parseCoreID parses the core id field.
-func parseCoreID(data string) (int64, error) {
-	return parseIntegerResult(data, coreIDKey)
-}
-
-// parseBugs grabs the bugs field from /proc/cpuinfo output.
-func parseBugs(data string) (map[string]struct{}, error) {
-	result, err := parseRegex(data, bugsKey, `[\d\w\s]*`)
-	if err != nil {
-		return nil, err
-	}
-	bugs := strings.Split(result, " ")
-	ret := make(map[string]struct{}, len(bugs))
-	for _, bug := range bugs {
-		ret[bug] = struct{}{}
-	}
-	return ret, nil
-}
-
-// parseIntegerResult parses fields expecting an integer.
-func parseIntegerResult(data, key string) (int64, error) {
-	result, err := parseRegex(data, key, `\d+`)
-	if err != nil {
-		return 0, err
-	}
-	return strconv.ParseInt(result, 0, 64)
-}
-
-// buildRegex builds a regex for parsing each CPU field.
-func buildRegex(key, match string) *regexp.Regexp {
-	reg := fmt.Sprintf(`(?m)^%s\s*:\s*(.*)$`, key)
-	return regexp.MustCompile(reg)
-}
-
-// parseRegex parses data with key inserted into a standard regex template.
-func parseRegex(data, key, match string) (string, error) {
-	r := buildRegex(key, match)
-	matches := r.FindStringSubmatch(data)
-	if len(matches) < 2 {
-		return "", fmt.Errorf("failed to match key %q: %q", key, data)
-	}
-	return matches[1], nil
-}
diff --git a/runsc/mitigate/mitigate.go b/runsc/mitigate/mitigate.go
index 91de623e3..24f67414c 100644
--- a/runsc/mitigate/mitigate.go
+++ b/runsc/mitigate/mitigate.go
@@ -14,121 +14,440 @@
 
 // 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.
+// shuts down CPUs via /sys/devices/system/cpu/cpu{N}/online.
 package mitigate
 
 import (
 	"fmt"
 	"io/ioutil"
-
-	"gvisor.dev/gvisor/pkg/log"
-	"gvisor.dev/gvisor/runsc/flag"
+	"os"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
 )
 
 const (
-	cpuInfo         = "/proc/cpuinfo"
-	allPossibleCPUs = "/sys/devices/system/cpu/possible"
+	// mds is the only bug we care about.
+	mds = "mds"
+
+	// Constants for parsing /proc/cpuinfo.
+	processorKey  = "processor"
+	vendorIDKey   = "vendor_id"
+	cpuFamilyKey  = "cpu family"
+	modelKey      = "model"
+	physicalIDKey = "physical id"
+	coreIDKey     = "core id"
+	bugsKey       = "bugs"
+
+	// Path to shutdown a CPU.
+	cpuOnlineTemplate = "/sys/devices/system/cpu/cpu%d/online"
 )
 
-// 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).
+// CPUSet contains a map of all CPUs on the system, mapped
+// by Physical ID and CoreIDs. threads with the same
+// Core and Physical ID are Hyperthread pairs.
+type CPUSet map[threadID]*ThreadGroup
+
+// NewCPUSet creates a CPUSet from data read from /proc/cpuinfo.
+func NewCPUSet(data []byte, vulnerable func(Thread) bool) (CPUSet, error) {
+	processors, err := getThreads(string(data))
+	if err != nil {
+		return nil, err
+	}
+
+	set := make(CPUSet)
+	for _, p := range processors {
+		// Each ID is of the form physicalID:coreID. Hyperthread pairs
+		// have identical physical and core IDs. We need to match
+		// Hyperthread pairs so that we can shutdown all but one per
+		// pair.
+		core, ok := set[p.id]
+		if !ok {
+			core = &ThreadGroup{}
+			set[p.id] = core
+		}
+		core.isVulnerable = core.isVulnerable || vulnerable(p)
+		core.threads = append(core.threads, p)
+	}
+
+	// We need to make sure we shutdown the lowest number processor per
+	// thread group.
+	for _, tg := range set {
+		sort.Slice(tg.threads, func(i, j int) bool {
+			return tg.threads[i].processorNumber < tg.threads[j].processorNumber
+		})
+	}
+	return set, nil
 }
 
-// Usage implments Usage for cmd.Mitigate.
-func (m Mitigate) Usage() string {
-	usageString := `mitigate [flags]
+// NewCPUSetFromPossible makes a cpuSet data read from
+// /sys/devices/system/cpu/possible. This is used in enable operations
+// where the caller simply wants to enable all CPUS.
+func NewCPUSetFromPossible(data []byte) (CPUSet, error) {
+	threads, err := GetThreadsFromPossible(data)
+	if err != nil {
+		return nil, err
+	}
+
+	// We don't care if a CPU is vulnerable or not, we just
+	// want to return a list of all CPUs on the host.
+	set := CPUSet{
+		threads[0].id: &ThreadGroup{
+			threads:      threads,
+			isVulnerable: false,
+		},
+	}
+	return set, nil
+}
 
-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.
+// String implements the String method for CPUSet.
+func (c CPUSet) String() string {
+	ret := ""
+	for _, tg := range c {
+		ret += fmt.Sprintf("%s\n", tg)
+	}
+	return ret
+}
 
-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()
+// GetRemainingList returns the list of threads that will remain active
+// after mitigation.
+func (c CPUSet) GetRemainingList() []Thread {
+	threads := make([]Thread, 0, len(c))
+	for _, core := range c {
+		// If we're vulnerable, take only one thread from the pair.
+		if core.isVulnerable {
+			threads = append(threads, core.threads[0])
+			continue
+		}
+		// Otherwise don't shutdown anything.
+		threads = append(threads, core.threads...)
+	}
+	return threads
 }
 
-// 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
+// GetShutdownList returns the list of threads that will be shutdown on
+// mitigation.
+func (c CPUSet) GetShutdownList() []Thread {
+	threads := make([]Thread, 0)
+	for _, core := range c {
+		// Only if we're vulnerable do shutdown anything. In this case,
+		// shutdown all but the first entry.
+		if core.isVulnerable && len(core.threads) > 1 {
+			threads = append(threads, core.threads[1:]...)
+		}
 	}
+	return threads
 }
 
-// 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)
+// ThreadGroup represents Hyperthread pairs on the same physical/core ID.
+type ThreadGroup struct {
+	threads      []Thread
+	isVulnerable bool
+}
+
+// String implements the String method for threadGroup.
+func (c ThreadGroup) String() string {
+	ret := fmt.Sprintf("ThreadGroup:\nIsVulnerable: %t\n", c.isVulnerable)
+	for _, processor := range c.threads {
+		ret += fmt.Sprintf("%s\n", processor)
 	}
+	return ret
+}
 
-	if m.reverse {
-		err := m.doReverse(data)
+// getThreads returns threads structs from reading /proc/cpuinfo.
+func getThreads(data string) ([]Thread, error) {
+	// Each processor entry should start with the
+	// processor key. Find the beginings of each.
+	r := buildRegex(processorKey, `\d+`)
+	indices := r.FindAllStringIndex(data, -1)
+	if len(indices) < 1 {
+		return nil, fmt.Errorf("no cpus found for: %q", data)
+	}
+
+	// Add the ending index for last entry.
+	indices = append(indices, []int{len(data), -1})
+
+	// Valid cpus are now defined by strings in between
+	// indexes (e.g. data[index[i], index[i+1]]).
+	// There should be len(indicies) - 1 CPUs
+	// since the last index is the end of the string.
+	cpus := make([]Thread, 0, len(indices))
+	// Find each string that represents a CPU. These begin "processor".
+	for i := 1; i < len(indices); i++ {
+		start := indices[i-1][0]
+		end := indices[i][0]
+		// Parse the CPU entry, which should be between start/end.
+		c, err := newThread(data[start:end])
 		if err != nil {
-			return fmt.Errorf("reverse operation failed: %v", err)
+			return nil, err
 		}
-		return nil
+		cpus = append(cpus, c)
+	}
+	return cpus, nil
+}
+
+// GetThreadsFromPossible makes threads from data read from /sys/devices/system/cpu/possible.
+func GetThreadsFromPossible(data []byte) ([]Thread, error) {
+	possibleRegex := regexp.MustCompile(`(?m)^(\d+)(-(\d+))?$`)
+	matches := possibleRegex.FindStringSubmatch(string(data))
+	if len(matches) != 4 {
+		return nil, fmt.Errorf("mismatch regex from possible: %q", string(data))
+	}
+
+	// If matches[3] is empty, we only have one cpu entry.
+	if matches[3] == "" {
+		matches[3] = matches[1]
 	}
 
-	set, err := m.doMitigate(data)
+	begin, err := strconv.ParseInt(matches[1], 10, 64)
 	if err != nil {
-		return fmt.Errorf("mitigate operation failed: %v", err)
+		return nil, fmt.Errorf("failed to parse begin: %v", err)
 	}
-	return m.other.execute(set, m.dryRun)
+	end, err := strconv.ParseInt(matches[3], 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse end: %v", err)
+	}
+	if begin > end || begin < 0 || end < 0 {
+		return nil, fmt.Errorf("invalid cpu bounds from possible: begin: %d end: %d", begin, end)
+	}
+
+	ret := make([]Thread, 0, end-begin)
+	for i := begin; i <= end; i++ {
+		ret = append(ret, Thread{
+			processorNumber: i,
+			id: threadID{
+				physicalID: 0, // we don't care about id for enable ops.
+				coreID:     0,
+			},
+		})
+	}
+
+	return ret, nil
+}
+
+// threadID for each thread is defined by the physical and
+// core IDs. If equal, two threads are Hyperthread pairs.
+type threadID struct {
+	physicalID int64
+	coreID     int64
 }
 
-func (m Mitigate) doMitigate(data []byte) (cpuSet, error) {
-	set, err := newCPUSet(data, m.other.vulnerable)
+// Thread represents pertinent info about a single hyperthread in a pair.
+type Thread struct {
+	processorNumber int64               // the processor number of this CPU.
+	vendorID        string              // the vendorID of CPU (e.g. AuthenticAMD).
+	cpuFamily       int64               // CPU family number (e.g. 6 for CascadeLake/Skylake).
+	model           int64               // CPU model number (e.g. 85 for CascadeLake/Skylake).
+	id              threadID            // id for this thread
+	bugs            map[string]struct{} // map of vulnerabilities parsed from the 'bugs' field.
+}
+
+// newThread parses a CPU from a single cpu entry from /proc/cpuinfo.
+func newThread(data string) (Thread, error) {
+	empty := Thread{}
+	processor, err := parseProcessor(data)
 	if err != nil {
-		return nil, err
+		return empty, err
 	}
 
-	log.Infof("Mitigate found the following CPUs...")
-	log.Infof("%s", set)
+	vendorID, err := parseVendorID(data)
+	if err != nil {
+		return empty, err
+	}
 
-	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)
-		}
+	cpuFamily, err := parseCPUFamily(data)
+	if err != nil {
+		return empty, err
 	}
-	log.Infof("Shutdown successful.")
-	return set, nil
+
+	model, err := parseModel(data)
+	if err != nil {
+		return empty, err
+	}
+
+	physicalID, err := parsePhysicalID(data)
+	if err != nil {
+		return empty, err
+	}
+
+	coreID, err := parseCoreID(data)
+	if err != nil {
+		return empty, err
+	}
+
+	bugs, err := parseBugs(data)
+	if err != nil {
+		return empty, err
+	}
+
+	return Thread{
+		processorNumber: processor,
+		vendorID:        vendorID,
+		cpuFamily:       cpuFamily,
+		model:           model,
+		id: threadID{
+			physicalID: physicalID,
+			coreID:     coreID,
+		},
+		bugs: bugs,
+	}, nil
+}
+
+// String implements the String method for thread.
+func (t Thread) String() string {
+	template := `CPU: %d
+CPU ID: %+v
+Vendor: %s
+Family/Model: %d/%d
+Bugs: %s
+`
+	bugs := make([]string, 0)
+	for bug := range t.bugs {
+		bugs = append(bugs, bug)
+	}
+
+	return fmt.Sprintf(template, t.processorNumber, t.id, t.vendorID, t.cpuFamily, t.model, strings.Join(bugs, ","))
+}
+
+// Enable turns on the CPU by writing 1 to /sys/devices/cpu/cpu{N}/online.
+func (t Thread) Enable() error {
+	// Linux ensures that "cpu0" is always online.
+	if t.processorNumber == 0 {
+		return nil
+	}
+	cpuPath := fmt.Sprintf(cpuOnlineTemplate, t.processorNumber)
+	f, err := os.OpenFile(cpuPath, os.O_WRONLY|os.O_CREATE, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to open file %s: %v", cpuPath, err)
+	}
+	if _, err = f.Write([]byte{'1'}); err != nil {
+		return fmt.Errorf("failed to write '1' to %s: %v", cpuPath, err)
+	}
+	return nil
+}
+
+// Disable turns off the CPU by writing 0 to /sys/devices/cpu/cpu{N}/online.
+func (t Thread) Disable() error {
+	// The core labeled "cpu0" can never be taken offline via this method.
+	// Linux will return EPERM if the user even creates a file at the /sys
+	// path above.
+	if t.processorNumber == 0 {
+		return fmt.Errorf("invalid shutdown operation: cpu0 cannot be disabled")
+	}
+	cpuPath := fmt.Sprintf(cpuOnlineTemplate, t.processorNumber)
+	return ioutil.WriteFile(cpuPath, []byte{'0'}, 0644)
 }
 
-func (m Mitigate) doReverse(data []byte) error {
-	set, err := newCPUSetFromPossible(data)
+// IsVulnerable checks if a CPU is vulnerable to mds.
+func (t Thread) IsVulnerable() bool {
+	_, ok := t.bugs[mds]
+	return ok
+}
+
+// isActive checks if a CPU is active from /sys/devices/system/cpu/cpu{N}/online
+// If the file does not exist (ioutil returns in error), we assume the CPU is on.
+func (t Thread) isActive() bool {
+	cpuPath := fmt.Sprintf(cpuOnlineTemplate, t.processorNumber)
+	data, err := ioutil.ReadFile(cpuPath)
 	if err != nil {
-		return err
+		return true
 	}
+	return len(data) > 0 && data[0] != '0'
+}
 
-	log.Infof("Reverse mitigate found the following CPUs...")
-	log.Infof("%s", set)
+// SimilarTo checks family/model/bugs fields for equality of two
+// processors.
+func (t Thread) SimilarTo(other Thread) bool {
+	if t.vendorID != other.vendorID {
+		return false
+	}
 
-	enableList := set.getRemainingList()
+	if other.cpuFamily != t.cpuFamily {
+		return false
+	}
 
-	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)
+	if other.model != t.model {
+		return false
+	}
+
+	if len(other.bugs) != len(t.bugs) {
+		return false
+	}
+
+	for bug := range t.bugs {
+		if _, ok := other.bugs[bug]; !ok {
+			return false
 		}
 	}
-	log.Infof("Enable successful.")
-	return nil
+	return true
+}
+
+// parseProcessor grabs the processor field from /proc/cpuinfo output.
+func parseProcessor(data string) (int64, error) {
+	return parseIntegerResult(data, processorKey)
+}
+
+// parseVendorID grabs the vendor_id field from /proc/cpuinfo output.
+func parseVendorID(data string) (string, error) {
+	return parseRegex(data, vendorIDKey, `[\w\d]+`)
+}
+
+// parseCPUFamily grabs the cpu family field from /proc/cpuinfo output.
+func parseCPUFamily(data string) (int64, error) {
+	return parseIntegerResult(data, cpuFamilyKey)
+}
+
+// parseModel grabs the model field from /proc/cpuinfo output.
+func parseModel(data string) (int64, error) {
+	return parseIntegerResult(data, modelKey)
+}
+
+// parsePhysicalID parses the physical id field.
+func parsePhysicalID(data string) (int64, error) {
+	return parseIntegerResult(data, physicalIDKey)
+}
+
+// parseCoreID parses the core id field.
+func parseCoreID(data string) (int64, error) {
+	return parseIntegerResult(data, coreIDKey)
+}
+
+// parseBugs grabs the bugs field from /proc/cpuinfo output.
+func parseBugs(data string) (map[string]struct{}, error) {
+	result, err := parseRegex(data, bugsKey, `[\d\w\s]*`)
+	if err != nil {
+		return nil, err
+	}
+	bugs := strings.Split(result, " ")
+	ret := make(map[string]struct{}, len(bugs))
+	for _, bug := range bugs {
+		ret[bug] = struct{}{}
+	}
+	return ret, nil
+}
+
+// parseIntegerResult parses fields expecting an integer.
+func parseIntegerResult(data, key string) (int64, error) {
+	result, err := parseRegex(data, key, `\d+`)
+	if err != nil {
+		return 0, err
+	}
+	return strconv.ParseInt(result, 0, 64)
+}
+
+// buildRegex builds a regex for parsing each CPU field.
+func buildRegex(key, match string) *regexp.Regexp {
+	reg := fmt.Sprintf(`(?m)^%s\s*:\s*(.*)$`, key)
+	return regexp.MustCompile(reg)
+}
+
+// parseRegex parses data with key inserted into a standard regex template.
+func parseRegex(data, key, match string) (string, error) {
+	r := buildRegex(key, match)
+	matches := r.FindStringSubmatch(data)
+	if len(matches) < 2 {
+		return "", fmt.Errorf("failed to match key %q: %q", key, data)
+	}
+	return matches[1], nil
 }
diff --git a/runsc/mitigate/mitigate_conf.go b/runsc/mitigate/mitigate_conf.go
deleted file mode 100644
index ee326324b..000000000
--- a/runsc/mitigate/mitigate_conf.go
+++ /dev/null
@@ -1,37 +0,0 @@
-// 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
-
-import (
-	"gvisor.dev/gvisor/runsc/flag"
-)
-
-type mitigate struct {
-}
-
-// usage returns the usage string portion for the mitigate.
-func (m mitigate) usage() string { return "" }
-
-// setFlags sets additional flags for the Mitigate command.
-func (m mitigate) setFlags(f *flag.FlagSet) {}
-
-// execute performs additional parts of Execute for Mitigate.
-func (m mitigate) execute(set cpuSet, dryrun bool) error {
-	return nil
-}
-
-func (m mitigate) vulnerable(other thread) bool {
-	return other.isVulnerable()
-}