8 files changed, 183 insertions, 10 deletions
diff --git a/pkg/atomicbitops/BUILD b/pkg/atomicbitops/BUILD
index 1a30f6967..11072d4de 100644
--- a/pkg/atomicbitops/BUILD
+++ b/pkg/atomicbitops/BUILD
@@ -5,6 +5,8 @@ package(licenses = ["notice"])
 go_library(
     name = "atomicbitops",
     srcs = [
+        "aligned_32bit_unsafe.go",
+        "aligned_64bit.go",
         "atomicbitops.go",
         "atomicbitops_amd64.s",
         "atomicbitops_arm64.s",
diff --git a/pkg/atomicbitops/aligned_32bit_unsafe.go b/pkg/atomicbitops/aligned_32bit_unsafe.go
new file mode 100644
index 000000000..776da53b0
--- /dev/null
+++ b/pkg/atomicbitops/aligned_32bit_unsafe.go
@@ -0,0 +1,96 @@
+// 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.
+
+// +build arm 386
+
+package atomicbitops
+
+import (
+	"sync/atomic"
+	"unsafe"
+)
+
+// AlignedAtomicInt64 is an atomic int64 that is guaranteed to be 64-bit
+// aligned, even on 32-bit systems.
+//
+// Per https://golang.org/pkg/sync/atomic/#pkg-note-BUG:
+//
+// "On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
+// for 64-bit alignment of 64-bit words accessed atomically. The first word in
+// a variable or in an allocated struct, array, or slice can be relied upon to
+// be 64-bit aligned."
+//
+// +stateify savable
+type AlignedAtomicInt64 struct {
+	value [15]byte
+}
+
+func (aa *AlignedAtomicInt64) ptr() *int64 {
+	// In the 15-byte aa.value, there are guaranteed to be 8 contiguous
+	// bytes with 64-bit alignment. We find an address in this range by
+	// adding 7, then clear the 3 least significant bits to get its start.
+	return (*int64)(unsafe.Pointer((uintptr(unsafe.Pointer(&aa.value[0])) + 7) &^ 7))
+}
+
+// Load is analagous to atomic.LoadInt64.
+func (aa *AlignedAtomicInt64) Load() int64 {
+	return atomic.LoadInt64(aa.ptr())
+}
+
+// Store is analagous to atomic.StoreInt64.
+func (aa *AlignedAtomicInt64) Store(v int64) {
+	atomic.StoreInt64(aa.ptr(), v)
+}
+
+// Add is analagous to atomic.AddInt64.
+func (aa *AlignedAtomicInt64) Add(v int64) int64 {
+	return atomic.AddInt64(aa.ptr(), v)
+}
+
+// AlignedAtomicUint64 is an atomic uint64 that is guaranteed to be 64-bit
+// aligned, even on 32-bit systems.
+//
+// Per https://golang.org/pkg/sync/atomic/#pkg-note-BUG:
+//
+// "On ARM, 386, and 32-bit MIPS, it is the caller's responsibility to arrange
+// for 64-bit alignment of 64-bit words accessed atomically. The first word in
+// a variable or in an allocated struct, array, or slice can be relied upon to
+// be 64-bit aligned."
+//
+// +stateify savable
+type AlignedAtomicUint64 struct {
+	value [15]byte
+}
+
+func (aa *AlignedAtomicUint64) ptr() *uint64 {
+	// In the 15-byte aa.value, there are guaranteed to be 8 contiguous
+	// bytes with 64-bit alignment. We find an address in this range by
+	// adding 7, then clear the 3 least significant bits to get its start.
+	return (*uint64)(unsafe.Pointer((uintptr(unsafe.Pointer(&aa.value[0])) + 7) &^ 7))
+}
+
+// Load is analagous to atomic.LoadUint64.
+func (aa *AlignedAtomicUint64) Load() uint64 {
+	return atomic.LoadUint64(aa.ptr())
+}
+
+// Store is analagous to atomic.StoreUint64.
+func (aa *AlignedAtomicUint64) Store(v uint64) {
+	atomic.StoreUint64(aa.ptr(), v)
+}
+
+// Add is analagous to atomic.AddUint64.
+func (aa *AlignedAtomicUint64) Add(v uint64) uint64 {
+	return atomic.AddUint64(aa.ptr(), v)
+}
diff --git a/pkg/atomicbitops/aligned_64bit.go b/pkg/atomicbitops/aligned_64bit.go
new file mode 100644
index 000000000..869ba40cd
--- /dev/null
+++ b/pkg/atomicbitops/aligned_64bit.go
@@ -0,0 +1,71 @@
+// 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.
+
+// +build amd64 arm64
+
+package atomicbitops
+
+import "sync/atomic"
+
+// AlignedAtomicInt64 is an atomic int64 that is guaranteed to be 64-bit
+// aligned, even on 32-bit systems. On 64-bit machines, it's just a regular
+// int64.
+//
+// See aligned_unsafe.go in this directory for justification.
+//
+// +stateify savable
+type AlignedAtomicInt64 struct {
+	value int64
+}
+
+// Load is analagous to atomic.LoadInt64.
+func (aa *AlignedAtomicInt64) Load() int64 {
+	return atomic.LoadInt64(&aa.value)
+}
+
+// Store is analagous to atomic.StoreInt64.
+func (aa *AlignedAtomicInt64) Store(v int64) {
+	atomic.StoreInt64(&aa.value, v)
+}
+
+// Add is analagous to atomic.AddInt64.
+func (aa *AlignedAtomicInt64) Add(v int64) int64 {
+	return atomic.AddInt64(&aa.value, v)
+}
+
+// AlignedAtomicUint64 is an atomic uint64 that is guaranteed to be 64-bit
+// aligned, even on 32-bit systems. On 64-bit machines, it's just a regular
+// uint64.
+//
+// See aligned_unsafe.go in this directory for justification.
+//
+// +stateify savable
+type AlignedAtomicUint64 struct {
+	value uint64
+}
+
+// Load is analagous to atomic.LoadUint64.
+func (aa *AlignedAtomicUint64) Load() uint64 {
+	return atomic.LoadUint64(&aa.value)
+}
+
+// Store is analagous to atomic.StoreUint64.
+func (aa *AlignedAtomicUint64) Store(v uint64) {
+	atomic.StoreUint64(&aa.value, v)
+}
+
+// Add is analagous to atomic.AddUint64.
+func (aa *AlignedAtomicUint64) Add(v uint64) uint64 {
+	return atomic.AddUint64(&aa.value, v)
+}
diff --git a/pkg/tcpip/BUILD b/pkg/tcpip/BUILD
index e96ba50ae..ea46c30da 100644
--- a/pkg/tcpip/BUILD
+++ b/pkg/tcpip/BUILD
@@ -29,6 +29,7 @@ go_library(
     ],
     visibility = ["//visibility:public"],
     deps = [
+        "//pkg/atomicbitops",
         "//pkg/sync",
         "//pkg/tcpip/buffer",
         "//pkg/waiter",
diff --git a/pkg/tcpip/socketops.go b/pkg/tcpip/socketops.go
index a6c877158..b26936b7f 100644
--- a/pkg/tcpip/socketops.go
+++ b/pkg/tcpip/socketops.go
@@ -18,6 +18,7 @@ import (
 	"math"
 	"sync/atomic"
 
+	"gvisor.dev/gvisor/pkg/atomicbitops"
 	"gvisor.dev/gvisor/pkg/sync"
 )
 
@@ -213,7 +214,7 @@ type SocketOptions struct {
 	getSendBufferLimits GetSendBufferLimits `state:"manual"`
 
 	// sendBufferSize determines the send buffer size for this socket.
-	sendBufferSize int64
+	sendBufferSize atomicbitops.AlignedAtomicInt64
 
 	// getReceiveBufferLimits provides the handler to get the min, default and
 	// max size for receive buffer. It is initialized at the creation time and
@@ -612,7 +613,7 @@ func (so *SocketOptions) SetBindToDevice(bindToDevice int32) Error {
 
 // GetSendBufferSize gets value for SO_SNDBUF option.
 func (so *SocketOptions) GetSendBufferSize() int64 {
-	return atomic.LoadInt64(&so.sendBufferSize)
+	return so.sendBufferSize.Load()
 }
 
 // SetSendBufferSize sets value for SO_SNDBUF option. notify indicates if the
@@ -621,7 +622,7 @@ func (so *SocketOptions) SetSendBufferSize(sendBufferSize int64, notify bool) {
 	v := sendBufferSize
 
 	if !notify {
-		atomic.StoreInt64(&so.sendBufferSize, v)
+		so.sendBufferSize.Store(v)
 		return
 	}
 
@@ -647,7 +648,7 @@ func (so *SocketOptions) SetSendBufferSize(sendBufferSize int64, notify bool) {
 
 	// Notify endpoint about change in buffer size.
 	newSz := so.handler.OnSetSendBufferSize(v)
-	atomic.StoreInt64(&so.sendBufferSize, newSz)
+	so.sendBufferSize.Store(newSz)
 }
 
 // GetReceiveBufferSize gets value for SO_RCVBUF option.
diff --git a/pkg/tcpip/stack/BUILD b/pkg/tcpip/stack/BUILD
index 2bd6a67f5..63ab31083 100644
--- a/pkg/tcpip/stack/BUILD
+++ b/pkg/tcpip/stack/BUILD
@@ -73,6 +73,7 @@ go_library(
     ],
     visibility = ["//visibility:public"],
     deps = [
+        "//pkg/atomicbitops",
         "//pkg/ilist",
         "//pkg/log",
         "//pkg/rand",
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 436392f23..3d9e1e286 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -29,6 +29,7 @@ import (
 	"time"
 
 	"golang.org/x/time/rate"
+	"gvisor.dev/gvisor/pkg/atomicbitops"
 	"gvisor.dev/gvisor/pkg/rand"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
@@ -65,10 +66,10 @@ type ResumableEndpoint interface {
 }
 
 // uniqueIDGenerator is a default unique ID generator.
-type uniqueIDGenerator uint64
+type uniqueIDGenerator atomicbitops.AlignedAtomicUint64
 
 func (u *uniqueIDGenerator) UniqueID() uint64 {
-	return atomic.AddUint64((*uint64)(u), 1)
+	return ((*atomicbitops.AlignedAtomicUint64)(u)).Add(1)
 }
 
 // Stack is a networking stack, with all supported protocols, NICs, and route
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index 6d7e22afe..f9acd4bb8 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -37,9 +37,9 @@ import (
 	"reflect"
 	"strconv"
 	"strings"
-	"sync/atomic"
 	"time"
 
+	"gvisor.dev/gvisor/pkg/atomicbitops"
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/waiter"
 )
@@ -1220,7 +1220,7 @@ type NetworkProtocolNumber uint32
 
 // A StatCounter keeps track of a statistic.
 type StatCounter struct {
-	count uint64
+	count atomicbitops.AlignedAtomicUint64
 }
 
 // Increment adds one to the counter.
@@ -1235,12 +1235,12 @@ func (s *StatCounter) Decrement() {
 
 // Value returns the current value of the counter.
 func (s *StatCounter) Value(name ...string) uint64 {
-	return atomic.LoadUint64(&s.count)
+	return s.count.Load()
 }
 
 // IncrementBy increments the counter by v.
 func (s *StatCounter) IncrementBy(v uint64) {
-	atomic.AddUint64(&s.count, v)
+	s.count.Add(v)
 }
 
 func (s *StatCounter) String() string {