Enable automated marshalling for epoll events.

Ensure we use the correct architecture-specific defintion of epoll
event, and use go-marshal for serialization.

PiperOrigin-RevId: 308145677

pkg/abi/linux/epoll_amd64.go

@@ -12,11 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build amd64
+
 package linux
 
 // EpollEvent is equivalent to struct epoll_event from epoll(2).
 //
-// +marshal
+// +marshal slice:EpollEventSlice
 type EpollEvent struct {
 	Events uint32
 	// Linux makes struct epoll_event::data a __u64. We represent it as

pkg/abi/linux/epoll_arm64.go

@@ -12,11 +12,13 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+// +build arm64
+
 package linux
 
 // EpollEvent is equivalent to struct epoll_event from epoll(2).
 //
-// +marshal
+// +marshal slice:EpollEventSlice
 type EpollEvent struct {
 	Events uint32
 	// Linux makes struct epoll_event a __u64, necessitating 4 bytes of padding

pkg/sentry/kernel/epoll/BUILD

@@ -24,6 +24,7 @@ go_library(
     ],
     visibility = ["//pkg/sentry:internal"],
     deps = [
+        "//pkg/abi/linux",
         "//pkg/context",
         "//pkg/refs",
         "//pkg/sentry/fs",

pkg/sentry/kernel/epoll/epoll.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 	"syscall"
 
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/refs"
 	"gvisor.dev/gvisor/pkg/sentry/fs"
@@ -30,19 +31,6 @@ import (
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
-// Event describes the event mask that was observed and the user data to be
-// returned when one of the events occurs. It has this format to match the linux
-// format to avoid extra copying/allocation when writing events to userspace.
-type Event struct {
-	// Events is the event mask containing the set of events that have been
-	// observed on an entry.
-	Events uint32
-
-	// Data is an opaque 64-bit value provided by the caller when adding the
-	// entry, and returned to the caller when the entry reports an event.
-	Data [2]int32
-}
-
 // EntryFlags is a bitmask that holds an entry's flags.
 type EntryFlags int
 
@@ -227,9 +215,9 @@ func (e *EventPoll) Readiness(mask waiter.EventMask) waiter.EventMask {
 }
 
 // ReadEvents returns up to max available events.
-func (e *EventPoll) ReadEvents(max int) []Event {
+func (e *EventPoll) ReadEvents(max int) []linux.EpollEvent {
 	var local pollEntryList
-	var ret []Event
+	var ret []linux.EpollEvent
 
 	e.listsMu.Lock()
 
@@ -251,7 +239,7 @@ func (e *EventPoll) ReadEvents(max int) []Event {
 		}
 
 		// Add event to the array that will be returned to caller.
-		ret = append(ret, Event{
+		ret = append(ret, linux.EpollEvent{
 			Events: uint32(ready),
 			Data:   entry.userData,
 		})

pkg/sentry/syscalls/epoll.go

@@ -17,6 +17,7 @@ package syscalls
 import (
 	"time"
 
+	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/epoll"
 	ktime "gvisor.dev/gvisor/pkg/sentry/kernel/time"
@@ -118,7 +119,7 @@ func RemoveEpoll(t *kernel.Task, epfd int32, fd int32) error {
 }
 
 // WaitEpoll implements the epoll_wait(2) linux syscall.
-func WaitEpoll(t *kernel.Task, fd int32, max int, timeout int) ([]epoll.Event, error) {
+func WaitEpoll(t *kernel.Task, fd int32, max int, timeout int) ([]linux.EpollEvent, error) {
 	// Get epoll from the file descriptor.
 	epollfile := t.GetFile(fd)
 	if epollfile == nil {

pkg/sentry/syscalls/linux/sys_epoll.go

@@ -21,7 +21,6 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/kernel/epoll"
 	"gvisor.dev/gvisor/pkg/sentry/syscalls"
 	"gvisor.dev/gvisor/pkg/syserror"
-	"gvisor.dev/gvisor/pkg/usermem"
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
@@ -72,7 +71,7 @@ func EpollCtl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysc
 	var data [2]int32
 	if op != linux.EPOLL_CTL_DEL {
 		var e linux.EpollEvent
-		if _, err := t.CopyIn(eventAddr, &e); err != nil {
+		if _, err := e.CopyIn(t, eventAddr); err != nil {
 			return 0, nil, err
 		}
 
@@ -105,28 +104,6 @@ func EpollCtl(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysc
 	}
 }
 
-// copyOutEvents copies epoll events from the kernel to user memory.
-func copyOutEvents(t *kernel.Task, addr usermem.Addr, e []epoll.Event) error {
-	const itemLen = 12
-	buffLen := len(e) * itemLen
-	if _, ok := addr.AddLength(uint64(buffLen)); !ok {
-		return syserror.EFAULT
-	}
-
-	b := t.CopyScratchBuffer(buffLen)
-	for i := range e {
-		usermem.ByteOrder.PutUint32(b[i*itemLen:], e[i].Events)
-		usermem.ByteOrder.PutUint32(b[i*itemLen+4:], uint32(e[i].Data[0]))
-		usermem.ByteOrder.PutUint32(b[i*itemLen+8:], uint32(e[i].Data[1]))
-	}
-
-	if _, err := t.CopyOutBytes(addr, b); err != nil {
-		return err
-	}
-
-	return nil
-}
-
 // EpollWait implements the epoll_wait(2) linux syscall.
 func EpollWait(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	epfd := args[0].Int()
@@ -140,7 +117,7 @@ func EpollWait(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sys
 	}
 
 	if len(r) != 0 {
-		if err := copyOutEvents(t, eventsAddr, r); err != nil {
+		if _, err := linux.CopyEpollEventSliceOut(t, eventsAddr, r); err != nil {
 			return 0, nil, err
 		}
 	}

pkg/sentry/syscalls/linux/vfs2/BUILD

@@ -6,7 +6,6 @@ go_library(
     name = "vfs2",
     srcs = [
         "epoll.go",
-        "epoll_unsafe.go",
         "execve.go",
         "fd.go",
         "filesystem.go",

pkg/sentry/syscalls/linux/vfs2/epoll.go

@@ -28,6 +28,8 @@ import (
 	"gvisor.dev/gvisor/pkg/waiter"
 )
 
+var sizeofEpollEvent = (*linux.EpollEvent)(nil).SizeBytes()
+
 // EpollCreate1 implements Linux syscall epoll_create1(2).
 func EpollCreate1(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
 	flags := args[0].Int()
@@ -124,7 +126,7 @@ func EpollWait(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sys
 	maxEvents := int(args[2].Int())
 	timeout := int(args[3].Int())
 
-	const _EP_MAX_EVENTS = math.MaxInt32 / sizeofEpollEvent // Linux: fs/eventpoll.c:EP_MAX_EVENTS
+	var _EP_MAX_EVENTS = math.MaxInt32 / sizeofEpollEvent // Linux: fs/eventpoll.c:EP_MAX_EVENTS
 	if maxEvents <= 0 || maxEvents > _EP_MAX_EVENTS {
 		return 0, nil, syserror.EINVAL
 	}
@@ -157,7 +159,8 @@ func EpollWait(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sys
 		maxEvents -= n
 		if n != 0 {
 			// Copy what we read out.
-			copiedEvents, err := copyOutEvents(t, eventsAddr, events[:n])
+			copiedBytes, err := linux.CopyEpollEventSliceOut(t, eventsAddr, events[:n])
+			copiedEvents := copiedBytes / sizeofEpollEvent // rounded down
 			eventsAddr += usermem.Addr(copiedEvents * sizeofEpollEvent)
 			total += copiedEvents
 			if err != nil {

pkg/sentry/syscalls/linux/vfs2/epoll_unsafe.go

@@ -1,44 +0,0 @@
-// Copyright 2020 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 vfs2
-
-import (
-	"reflect"
-	"runtime"
-	"unsafe"
-
-	"gvisor.dev/gvisor/pkg/abi/linux"
-	"gvisor.dev/gvisor/pkg/gohacks"
-	"gvisor.dev/gvisor/pkg/sentry/kernel"
-	"gvisor.dev/gvisor/pkg/usermem"
-)
-
-const sizeofEpollEvent = int(unsafe.Sizeof(linux.EpollEvent{}))
-
-func copyOutEvents(t *kernel.Task, addr usermem.Addr, events []linux.EpollEvent) (int, error) {
-	if len(events) == 0 {
-		return 0, nil
-	}
-	// Cast events to a byte slice for copying.
-	var eventBytes []byte
-	eventBytesHdr := (*reflect.SliceHeader)(unsafe.Pointer(&eventBytes))
-	eventBytesHdr.Data = uintptr(gohacks.Noescape(unsafe.Pointer(&events[0])))
-	eventBytesHdr.Len = len(events) * sizeofEpollEvent
-	eventBytesHdr.Cap = len(events) * sizeofEpollEvent
-	copiedBytes, err := t.CopyOutBytes(addr, eventBytes)
-	runtime.KeepAlive(events)
-	copiedEvents := copiedBytes / sizeofEpollEvent // rounded down
-	return copiedEvents, err
-}