3 files changed, 260 insertions, 41 deletions
diff --git a/pkg/sentry/kernel/shm/BUILD b/pkg/sentry/kernel/shm/BUILD
deleted file mode 100644
index b7e4b480d..000000000
--- a/pkg/sentry/kernel/shm/BUILD
+++ /dev/null
@@ -1,41 +0,0 @@
-load("//tools:defs.bzl", "go_library")
-load("//tools/go_generics:defs.bzl", "go_template_instance")
-
-package(licenses = ["notice"])
-
-go_template_instance(
-    name = "shm_refs",
-    out = "shm_refs.go",
-    package = "shm",
-    prefix = "Shm",
-    template = "//pkg/refs_vfs2:refs_template",
-    types = {
-        "T": "Shm",
-    },
-)
-
-go_library(
-    name = "shm",
-    srcs = [
-        "device.go",
-        "shm.go",
-        "shm_refs.go",
-    ],
-    visibility = ["//pkg/sentry:internal"],
-    deps = [
-        "//pkg/abi/linux",
-        "//pkg/context",
-        "//pkg/log",
-        "//pkg/refs",
-        "//pkg/sentry/device",
-        "//pkg/sentry/fs",
-        "//pkg/sentry/kernel/auth",
-        "//pkg/sentry/kernel/time",
-        "//pkg/sentry/memmap",
-        "//pkg/sentry/pgalloc",
-        "//pkg/sentry/usage",
-        "//pkg/sync",
-        "//pkg/syserror",
-        "//pkg/usermem",
-    ],
-)
diff --git a/pkg/sentry/kernel/shm/shm_refs.go b/pkg/sentry/kernel/shm/shm_refs.go
new file mode 100644
index 000000000..0da23fa5f
--- /dev/null
+++ b/pkg/sentry/kernel/shm/shm_refs.go
@@ -0,0 +1,118 @@
+package shm
+
+import (
+	"fmt"
+	refs_vfs1 "gvisor.dev/gvisor/pkg/refs"
+	"runtime"
+	"sync/atomic"
+
+	"gvisor.dev/gvisor/pkg/log"
+)
+
+// ownerType is used to customize logging. Note that we use a pointer to T so
+// that we do not copy the entire object when passed as a format parameter.
+var ShmownerType *Shm
+
+// Refs implements refs.RefCounter. It keeps a reference count using atomic
+// operations and calls the destructor when the count reaches zero.
+//
+// Note that the number of references is actually refCount + 1 so that a default
+// zero-value Refs object contains one reference.
+//
+// TODO(gvisor.dev/issue/1486): Store stack traces when leak check is enabled in
+// a map with 16-bit hashes, and store the hash in the top 16 bits of refCount.
+// This will allow us to add stack trace information to the leak messages
+// without growing the size of Refs.
+//
+// +stateify savable
+type ShmRefs struct {
+	// refCount is composed of two fields:
+	//
+	//	[32-bit speculative references]:[32-bit real references]
+	//
+	// Speculative references are used for TryIncRef, to avoid a CompareAndSwap
+	// loop. See IncRef, DecRef and TryIncRef for details of how these fields are
+	// used.
+	refCount int64
+}
+
+func (r *ShmRefs) finalize() {
+	var note string
+	switch refs_vfs1.GetLeakMode() {
+	case refs_vfs1.NoLeakChecking:
+		return
+	case refs_vfs1.UninitializedLeakChecking:
+		note = "(Leak checker uninitialized): "
+	}
+	if n := r.ReadRefs(); n != 0 {
+		log.Warningf("%sRefs %p owned by %T garbage collected with ref count of %d (want 0)", note, r, ShmownerType, n)
+	}
+}
+
+// EnableLeakCheck checks for reference leaks when Refs gets garbage collected.
+func (r *ShmRefs) EnableLeakCheck() {
+	if refs_vfs1.GetLeakMode() != refs_vfs1.NoLeakChecking {
+		runtime.SetFinalizer(r, (*ShmRefs).finalize)
+	}
+}
+
+// ReadRefs returns the current number of references. The returned count is
+// inherently racy and is unsafe to use without external synchronization.
+func (r *ShmRefs) ReadRefs() int64 {
+
+	return atomic.LoadInt64(&r.refCount) + 1
+}
+
+// IncRef implements refs.RefCounter.IncRef.
+//
+//go:nosplit
+func (r *ShmRefs) IncRef() {
+	if v := atomic.AddInt64(&r.refCount, 1); v <= 0 {
+		panic(fmt.Sprintf("Incrementing non-positive ref count %p owned by %T", r, ShmownerType))
+	}
+}
+
+// TryIncRef implements refs.RefCounter.TryIncRef.
+//
+// To do this safely without a loop, a speculative reference is first acquired
+// on the object. This allows multiple concurrent TryIncRef calls to distinguish
+// other TryIncRef calls from genuine references held.
+//
+//go:nosplit
+func (r *ShmRefs) TryIncRef() bool {
+	const speculativeRef = 1 << 32
+	v := atomic.AddInt64(&r.refCount, speculativeRef)
+	if int32(v) < 0 {
+
+		atomic.AddInt64(&r.refCount, -speculativeRef)
+		return false
+	}
+
+	atomic.AddInt64(&r.refCount, -speculativeRef+1)
+	return true
+}
+
+// DecRef implements refs.RefCounter.DecRef.
+//
+// Note that speculative references are counted here. Since they were added
+// prior to real references reaching zero, they will successfully convert to
+// real references. In other words, we see speculative references only in the
+// following case:
+//
+//	A: TryIncRef [speculative increase => sees non-negative references]
+//	B: DecRef [real decrease]
+//	A: TryIncRef [transform speculative to real]
+//
+//go:nosplit
+func (r *ShmRefs) DecRef(destroy func()) {
+	switch v := atomic.AddInt64(&r.refCount, -1); {
+	case v < -1:
+		panic(fmt.Sprintf("Decrementing non-positive ref count %p, owned by %T", r, ShmownerType))
+
+	case v == -1:
+
+		if destroy != nil {
+			destroy()
+		}
+	}
+}
diff --git a/pkg/sentry/kernel/shm/shm_state_autogen.go b/pkg/sentry/kernel/shm/shm_state_autogen.go
new file mode 100644
index 000000000..fa80353b6
--- /dev/null
+++ b/pkg/sentry/kernel/shm/shm_state_autogen.go
@@ -0,0 +1,142 @@
+// automatically generated by stateify.
+
+package shm
+
+import (
+	"gvisor.dev/gvisor/pkg/state"
+)
+
+func (x *Registry) StateTypeName() string {
+	return "pkg/sentry/kernel/shm.Registry"
+}
+
+func (x *Registry) StateFields() []string {
+	return []string{
+		"userNS",
+		"shms",
+		"keysToShms",
+		"totalPages",
+		"lastIDUsed",
+	}
+}
+
+func (x *Registry) beforeSave() {}
+
+func (x *Registry) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.userNS)
+	m.Save(1, &x.shms)
+	m.Save(2, &x.keysToShms)
+	m.Save(3, &x.totalPages)
+	m.Save(4, &x.lastIDUsed)
+}
+
+func (x *Registry) afterLoad() {}
+
+func (x *Registry) StateLoad(m state.Source) {
+	m.Load(0, &x.userNS)
+	m.Load(1, &x.shms)
+	m.Load(2, &x.keysToShms)
+	m.Load(3, &x.totalPages)
+	m.Load(4, &x.lastIDUsed)
+}
+
+func (x *Shm) StateTypeName() string {
+	return "pkg/sentry/kernel/shm.Shm"
+}
+
+func (x *Shm) StateFields() []string {
+	return []string{
+		"ShmRefs",
+		"mfp",
+		"registry",
+		"ID",
+		"creator",
+		"size",
+		"effectiveSize",
+		"fr",
+		"key",
+		"perms",
+		"owner",
+		"attachTime",
+		"detachTime",
+		"changeTime",
+		"creatorPID",
+		"lastAttachDetachPID",
+		"pendingDestruction",
+	}
+}
+
+func (x *Shm) beforeSave() {}
+
+func (x *Shm) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.ShmRefs)
+	m.Save(1, &x.mfp)
+	m.Save(2, &x.registry)
+	m.Save(3, &x.ID)
+	m.Save(4, &x.creator)
+	m.Save(5, &x.size)
+	m.Save(6, &x.effectiveSize)
+	m.Save(7, &x.fr)
+	m.Save(8, &x.key)
+	m.Save(9, &x.perms)
+	m.Save(10, &x.owner)
+	m.Save(11, &x.attachTime)
+	m.Save(12, &x.detachTime)
+	m.Save(13, &x.changeTime)
+	m.Save(14, &x.creatorPID)
+	m.Save(15, &x.lastAttachDetachPID)
+	m.Save(16, &x.pendingDestruction)
+}
+
+func (x *Shm) afterLoad() {}
+
+func (x *Shm) StateLoad(m state.Source) {
+	m.Load(0, &x.ShmRefs)
+	m.Load(1, &x.mfp)
+	m.Load(2, &x.registry)
+	m.Load(3, &x.ID)
+	m.Load(4, &x.creator)
+	m.Load(5, &x.size)
+	m.Load(6, &x.effectiveSize)
+	m.Load(7, &x.fr)
+	m.Load(8, &x.key)
+	m.Load(9, &x.perms)
+	m.Load(10, &x.owner)
+	m.Load(11, &x.attachTime)
+	m.Load(12, &x.detachTime)
+	m.Load(13, &x.changeTime)
+	m.Load(14, &x.creatorPID)
+	m.Load(15, &x.lastAttachDetachPID)
+	m.Load(16, &x.pendingDestruction)
+}
+
+func (x *ShmRefs) StateTypeName() string {
+	return "pkg/sentry/kernel/shm.ShmRefs"
+}
+
+func (x *ShmRefs) StateFields() []string {
+	return []string{
+		"refCount",
+	}
+}
+
+func (x *ShmRefs) beforeSave() {}
+
+func (x *ShmRefs) StateSave(m state.Sink) {
+	x.beforeSave()
+	m.Save(0, &x.refCount)
+}
+
+func (x *ShmRefs) afterLoad() {}
+
+func (x *ShmRefs) StateLoad(m state.Source) {
+	m.Load(0, &x.refCount)
+}
+
+func init() {
+	state.Register((*Registry)(nil))
+	state.Register((*Shm)(nil))
+	state.Register((*ShmRefs)(nil))
+}