Port signalfd to vfs2.

PiperOrigin-RevId: 310404113

10 files changed, 272 insertions, 10 deletions

diff --git a/pkg/sentry/fsimpl/signalfd/BUILD b/pkg/sentry/fsimpl/signalfd/BUILD
new file mode 100644
index 000000000..067c1657f
--- /dev/null
+++ b/pkg/sentry/fsimpl/signalfd/BUILD
@@ -0,0 +1,20 @@
+load("//tools:defs.bzl", "go_library")
+
+package(licenses = ["notice"])
+
+go_library(
+    name = "signalfd",
+    srcs = ["signalfd.go"],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/abi/linux",
+        "//pkg/binary",
+        "//pkg/context",
+        "//pkg/sentry/kernel",
+        "//pkg/sentry/vfs",
+        "//pkg/sync",
+        "//pkg/syserror",
+        "//pkg/usermem",
+        "//pkg/waiter",
+    ],
+)
diff --git a/pkg/sentry/fsimpl/signalfd/signalfd.go b/pkg/sentry/fsimpl/signalfd/signalfd.go
new file mode 100644
index 000000000..d29ef3f83
--- /dev/null
+++ b/pkg/sentry/fsimpl/signalfd/signalfd.go
@@ -0,0 +1,135 @@
+// Copyright 2019 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 signalfd
+
+import (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/binary"
+	"gvisor.dev/gvisor/pkg/context"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/vfs"
+	"gvisor.dev/gvisor/pkg/sync"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+	"gvisor.dev/gvisor/pkg/waiter"
+)
+
+// SignalFileDescription implements FileDescriptionImpl for signal fds.
+type SignalFileDescription struct {
+	vfsfd vfs.FileDescription
+	vfs.FileDescriptionDefaultImpl
+	vfs.DentryMetadataFileDescriptionImpl
+
+	// target is the original signal target task.
+	//
+	// The semantics here are a bit broken. Linux will always use current
+	// for all reads, regardless of where the signalfd originated. We can't
+	// do exactly that because we need to plumb the context through
+	// EventRegister in order to support proper blocking behavior. This
+	// will undoubtedly become very complicated quickly.
+	target *kernel.Task
+
+	// mu protects mask.
+	mu sync.Mutex
+
+	// mask is the signal mask. Protected by mu.
+	mask linux.SignalSet
+}
+
+var _ vfs.FileDescriptionImpl = (*SignalFileDescription)(nil)
+
+// New creates a new signal fd.
+func New(vfsObj *vfs.VirtualFilesystem, target *kernel.Task, mask linux.SignalSet, flags uint32) (*vfs.FileDescription, error) {
+	vd := vfsObj.NewAnonVirtualDentry("[signalfd]")
+	defer vd.DecRef()
+	sfd := &SignalFileDescription{
+		target: target,
+		mask:   mask,
+	}
+	if err := sfd.vfsfd.Init(sfd, flags, vd.Mount(), vd.Dentry(), &vfs.FileDescriptionOptions{
+		UseDentryMetadata: true,
+		DenyPRead:         true,
+		DenyPWrite:        true,
+	}); err != nil {
+		return nil, err
+	}
+	return &sfd.vfsfd, nil
+}
+
+// Mask returns the signal mask.
+func (sfd *SignalFileDescription) Mask() linux.SignalSet {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	return sfd.mask
+}
+
+// SetMask sets the signal mask.
+func (sfd *SignalFileDescription) SetMask(mask linux.SignalSet) {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	sfd.mask = mask
+}
+
+// Read implements FileDescriptionImpl.Read.
+func (sfd *SignalFileDescription) Read(ctx context.Context, dst usermem.IOSequence, _ vfs.ReadOptions) (int64, error) {
+	// Attempt to dequeue relevant signals.
+	info, err := sfd.target.Sigtimedwait(sfd.Mask(), 0)
+	if err != nil {
+		// There must be no signal available.
+		return 0, syserror.ErrWouldBlock
+	}
+
+	// Copy out the signal info using the specified format.
+	var buf [128]byte
+	binary.Marshal(buf[:0], usermem.ByteOrder, &linux.SignalfdSiginfo{
+		Signo:   uint32(info.Signo),
+		Errno:   info.Errno,
+		Code:    info.Code,
+		PID:     uint32(info.Pid()),
+		UID:     uint32(info.Uid()),
+		Status:  info.Status(),
+		Overrun: uint32(info.Overrun()),
+		Addr:    info.Addr(),
+	})
+	n, err := dst.CopyOut(ctx, buf[:])
+	return int64(n), err
+}
+
+// Readiness implements waiter.Waitable.Readiness.
+func (sfd *SignalFileDescription) Readiness(mask waiter.EventMask) waiter.EventMask {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	if mask&waiter.EventIn != 0 && sfd.target.PendingSignals()&sfd.mask != 0 {
+		return waiter.EventIn // Pending signals.
+	}
+	return 0
+}
+
+// EventRegister implements waiter.Waitable.EventRegister.
+func (sfd *SignalFileDescription) EventRegister(entry *waiter.Entry, _ waiter.EventMask) {
+	sfd.mu.Lock()
+	defer sfd.mu.Unlock()
+	// Register for the signal set; ignore the passed events.
+	sfd.target.SignalRegister(entry, waiter.EventMask(sfd.mask))
+}
+
+// EventUnregister implements waiter.Waitable.EventUnregister.
+func (sfd *SignalFileDescription) EventUnregister(entry *waiter.Entry) {
+	// Unregister the original entry.
+	sfd.target.SignalUnregister(entry)
+}
+
+// Release implements FileDescriptionImpl.Release()
+func (sfd *SignalFileDescription) Release() {}
diff --git a/pkg/sentry/syscalls/linux/sigset.go b/pkg/sentry/syscalls/linux/sigset.go
index 2ddb2b146..434559b80 100644
--- a/pkg/sentry/syscalls/linux/sigset.go
+++ b/pkg/sentry/syscalls/linux/sigset.go
@@ -21,9 +21,13 @@ import (
 	"gvisor.dev/gvisor/pkg/usermem"
 )
 
-// copyInSigSet copies in a sigset_t, checks its size, and ensures that KILL and
+// CopyInSigSet copies in a sigset_t, checks its size, and ensures that KILL and
 // STOP are clear.
-func copyInSigSet(t *kernel.Task, sigSetAddr usermem.Addr, size uint) (linux.SignalSet, error) {
+//
+// TODO(gvisor.dev/issue/1624): This is only exported because
+// syscalls/vfs2/signal.go depends on it. Once vfs1 is deleted and the vfs2
+// syscalls are moved into this package, then they can be unexported.
+func CopyInSigSet(t *kernel.Task, sigSetAddr usermem.Addr, size uint) (linux.SignalSet, error) {
 	if size != linux.SignalSetSize {
 		return 0, syserror.EINVAL
 	}
diff --git a/pkg/sentry/syscalls/linux/sys_epoll.go b/pkg/sentry/syscalls/linux/sys_epoll.go
index 51bf205cf..7f460d30b 100644
--- a/pkg/sentry/syscalls/linux/sys_epoll.go
+++ b/pkg/sentry/syscalls/linux/sys_epoll.go
@@ -131,7 +131,7 @@ func EpollPwait(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sy
 	maskSize := uint(args[5].Uint())
 
 	if maskAddr != 0 {
-		mask, err := copyInSigSet(t, maskAddr, maskSize)
+		mask, err := CopyInSigSet(t, maskAddr, maskSize)
 		if err != nil {
 			return 0, nil, err
 		}
diff --git a/pkg/sentry/syscalls/linux/sys_poll.go b/pkg/sentry/syscalls/linux/sys_poll.go
index 4f8762d7d..f0198141c 100644
--- a/pkg/sentry/syscalls/linux/sys_poll.go
+++ b/pkg/sentry/syscalls/linux/sys_poll.go
@@ -443,7 +443,7 @@ func Ppoll(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Syscall
 	}
 
 	if maskAddr != 0 {
-		mask, err := copyInSigSet(t, maskAddr, maskSize)
+		mask, err := CopyInSigSet(t, maskAddr, maskSize)
 		if err != nil {
 			return 0, nil, err
 		}
@@ -525,7 +525,7 @@ func Pselect(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.Sysca
 		}
 
 		if maskAddr != 0 {
-			mask, err := copyInSigSet(t, maskAddr, size)
+			mask, err := CopyInSigSet(t, maskAddr, size)
 			if err != nil {
 				return 0, nil, err
 			}
diff --git a/pkg/sentry/syscalls/linux/sys_signal.go b/pkg/sentry/syscalls/linux/sys_signal.go
index 582d37e03..d2b0012ae 100644
--- a/pkg/sentry/syscalls/linux/sys_signal.go
+++ b/pkg/sentry/syscalls/linux/sys_signal.go
@@ -295,7 +295,7 @@ func RtSigprocmask(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel
 	}
 	oldmask := t.SignalMask()
 	if setaddr != 0 {
-		mask, err := copyInSigSet(t, setaddr, sigsetsize)
+		mask, err := CopyInSigSet(t, setaddr, sigsetsize)
 		if err != nil {
 			return 0, nil, err
 		}
@@ -366,7 +366,7 @@ func RtSigtimedwait(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kerne
 	timespec := args[2].Pointer()
 	sigsetsize := args[3].SizeT()
 
-	mask, err := copyInSigSet(t, sigset, sigsetsize)
+	mask, err := CopyInSigSet(t, sigset, sigsetsize)
 	if err != nil {
 		return 0, nil, err
 	}
@@ -518,7 +518,7 @@ func RestartSyscall(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kerne
 // sharedSignalfd is shared between the two calls.
 func sharedSignalfd(t *kernel.Task, fd int32, sigset usermem.Addr, sigsetsize uint, flags int32) (uintptr, *kernel.SyscallControl, error) {
 	// Copy in the signal mask.
-	mask, err := copyInSigSet(t, sigset, sigsetsize)
+	mask, err := CopyInSigSet(t, sigset, sigsetsize)
 	if err != nil {
 		return 0, nil, err
 	}
diff --git a/pkg/sentry/syscalls/linux/vfs2/BUILD b/pkg/sentry/syscalls/linux/vfs2/BUILD
index 4c7b8f819..14838aa2c 100644
--- a/pkg/sentry/syscalls/linux/vfs2/BUILD
+++ b/pkg/sentry/syscalls/linux/vfs2/BUILD
@@ -19,6 +19,7 @@ go_library(
         "poll.go",
         "read_write.go",
         "setstat.go",
+        "signal.go",
         "socket.go",
         "stat.go",
         "stat_amd64.go",
@@ -39,6 +40,7 @@ go_library(
         "//pkg/sentry/arch",
         "//pkg/sentry/fsbridge",
         "//pkg/sentry/fsimpl/pipefs",
+        "//pkg/sentry/fsimpl/signalfd",
         "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/kernel/pipe",
diff --git a/pkg/sentry/syscalls/linux/vfs2/signal.go b/pkg/sentry/syscalls/linux/vfs2/signal.go
new file mode 100644
index 000000000..623992f6f
--- /dev/null
+++ b/pkg/sentry/syscalls/linux/vfs2/signal.go
@@ -0,0 +1,100 @@
+// Copyright 2018 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 (
+	"gvisor.dev/gvisor/pkg/abi/linux"
+	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/fsimpl/signalfd"
+	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	slinux "gvisor.dev/gvisor/pkg/sentry/syscalls/linux"
+	"gvisor.dev/gvisor/pkg/syserror"
+	"gvisor.dev/gvisor/pkg/usermem"
+)
+
+// sharedSignalfd is shared between the two calls.
+func sharedSignalfd(t *kernel.Task, fd int32, sigset usermem.Addr, sigsetsize uint, flags int32) (uintptr, *kernel.SyscallControl, error) {
+	// Copy in the signal mask.
+	mask, err := slinux.CopyInSigSet(t, sigset, sigsetsize)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	// Always check for valid flags, even if not creating.
+	if flags&^(linux.SFD_NONBLOCK|linux.SFD_CLOEXEC) != 0 {
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Is this a change to an existing signalfd?
+	//
+	// The spec indicates that this should adjust the mask.
+	if fd != -1 {
+		file := t.GetFileVFS2(fd)
+		if file == nil {
+			return 0, nil, syserror.EBADF
+		}
+		defer file.DecRef()
+
+		// Is this a signalfd?
+		if sfd, ok := file.Impl().(*signalfd.SignalFileDescription); ok {
+			sfd.SetMask(mask)
+			return 0, nil, nil
+		}
+
+		// Not a signalfd.
+		return 0, nil, syserror.EINVAL
+	}
+
+	fileFlags := uint32(linux.O_RDWR)
+	if flags&linux.SFD_NONBLOCK != 0 {
+		fileFlags |= linux.O_NONBLOCK
+	}
+
+	// Create a new file.
+	vfsObj := t.Kernel().VFS()
+	file, err := signalfd.New(vfsObj, t, mask, fileFlags)
+	if err != nil {
+		return 0, nil, err
+	}
+	defer file.DecRef()
+
+	// Create a new descriptor.
+	fd, err = t.NewFDFromVFS2(0, file, kernel.FDFlags{
+		CloseOnExec: flags&linux.SFD_CLOEXEC != 0,
+	})
+	if err != nil {
+		return 0, nil, err
+	}
+
+	// Done.
+	return uintptr(fd), nil, nil
+}
+
+// Signalfd implements the linux syscall signalfd(2).
+func Signalfd(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	fd := args[0].Int()
+	sigset := args[1].Pointer()
+	sigsetsize := args[2].SizeT()
+	return sharedSignalfd(t, fd, sigset, sigsetsize, 0)
+}
+
+// Signalfd4 implements the linux syscall signalfd4(2).
+func Signalfd4(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
+	fd := args[0].Int()
+	sigset := args[1].Pointer()
+	sigsetsize := args[2].SizeT()
+	flags := args[3].Int()
+	return sharedSignalfd(t, fd, sigset, sigsetsize, flags)
+}
diff --git a/pkg/sentry/syscalls/linux/vfs2/vfs2.go b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
index f1b697844..9c04677f1 100644
--- a/pkg/sentry/syscalls/linux/vfs2/vfs2.go
+++ b/pkg/sentry/syscalls/linux/vfs2/vfs2.go
@@ -139,14 +139,14 @@ func Override() {
 	s.Table[277] = syscalls.Supported("sync_file_range", SyncFileRange)
 	s.Table[280] = syscalls.Supported("utimensat", Utimensat)
 	s.Table[281] = syscalls.Supported("epoll_pwait", EpollPwait)
-	delete(s.Table, 282) // signalfd
+	s.Table[282] = syscalls.Supported("signalfd", Signalfd)
 	s.Table[283] = syscalls.Supported("timerfd_create", TimerfdCreate)
 	s.Table[284] = syscalls.Supported("eventfd", Eventfd)
 	delete(s.Table, 285) // fallocate
 	s.Table[286] = syscalls.Supported("timerfd_settime", TimerfdSettime)
 	s.Table[287] = syscalls.Supported("timerfd_gettime", TimerfdGettime)
 	s.Table[288] = syscalls.Supported("accept4", Accept4)
-	delete(s.Table, 289) // signalfd4
+	s.Table[289] = syscalls.Supported("signalfd4", Signalfd4)
 	s.Table[290] = syscalls.Supported("eventfd2", Eventfd2)
 	s.Table[291] = syscalls.Supported("epoll_create1", EpollCreate1)
 	s.Table[292] = syscalls.Supported("dup3", Dup3)
diff --git a/pkg/sentry/vfs/BUILD b/pkg/sentry/vfs/BUILD
index c62505fe2..86046dd99 100644
--- a/pkg/sentry/vfs/BUILD
+++ b/pkg/sentry/vfs/BUILD
@@ -43,6 +43,7 @@ go_library(
     visibility = ["//pkg/sentry:internal"],
     deps = [
         "//pkg/abi/linux",
+        "//pkg/binary",
         "//pkg/context",
         "//pkg/fd",
         "//pkg/fdnotifier",