3 files changed, 80 insertions, 2 deletions
diff --git a/pkg/sentry/syscalls/linux/BUILD b/pkg/sentry/syscalls/linux/BUILD
index 33a40b9c6..e76ee27d2 100644
--- a/pkg/sentry/syscalls/linux/BUILD
+++ b/pkg/sentry/syscalls/linux/BUILD
@@ -74,6 +74,7 @@ go_library(
         "//pkg/sentry/kernel/pipe",
         "//pkg/sentry/kernel/sched",
         "//pkg/sentry/kernel/shm",
+        "//pkg/sentry/kernel/signalfd",
         "//pkg/sentry/kernel/time",
         "//pkg/sentry/limits",
         "//pkg/sentry/memmap",
diff --git a/pkg/sentry/syscalls/linux/linux64.go b/pkg/sentry/syscalls/linux/linux64.go
index 150999fb8..18d24ab61 100644
--- a/pkg/sentry/syscalls/linux/linux64.go
+++ b/pkg/sentry/syscalls/linux/linux64.go
@@ -327,14 +327,14 @@ var AMD64 = &kernel.SyscallTable{
 		279: syscalls.CapError("move_pages", linux.CAP_SYS_NICE, "", nil),                               // requires cap_sys_nice (mostly)
 		280: syscalls.Supported("utimensat", Utimensat),
 		281: syscalls.Supported("epoll_pwait", EpollPwait),
-		282: syscalls.ErrorWithEvent("signalfd", syserror.ENOSYS, "", []string{"gvisor.dev/issue/139"}), // TODO(b/19846426)
+		282: syscalls.PartiallySupported("signalfd", Signalfd, "Semantics are slightly different.", []string{"gvisor.dev/issue/139"}),
 		283: syscalls.Supported("timerfd_create", TimerfdCreate),
 		284: syscalls.Supported("eventfd", Eventfd),
 		285: syscalls.PartiallySupported("fallocate", Fallocate, "Not all options are supported.", nil),
 		286: syscalls.Supported("timerfd_settime", TimerfdSettime),
 		287: syscalls.Supported("timerfd_gettime", TimerfdGettime),
 		288: syscalls.Supported("accept4", Accept4),
-		289: syscalls.ErrorWithEvent("signalfd4", syserror.ENOSYS, "", []string{"gvisor.dev/issue/139"}), // TODO(b/19846426)
+		289: syscalls.PartiallySupported("signalfd4", Signalfd4, "Semantics are slightly different.", []string{"gvisor.dev/issue/139"}),
 		290: syscalls.Supported("eventfd2", Eventfd2),
 		291: syscalls.Supported("epoll_create1", EpollCreate1),
 		292: syscalls.Supported("dup3", Dup3),
diff --git a/pkg/sentry/syscalls/linux/sys_signal.go b/pkg/sentry/syscalls/linux/sys_signal.go
index 0104a94c0..fb6efd5d8 100644
--- a/pkg/sentry/syscalls/linux/sys_signal.go
+++ b/pkg/sentry/syscalls/linux/sys_signal.go
@@ -20,7 +20,10 @@ import (
 
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/sentry/arch"
+	"gvisor.dev/gvisor/pkg/sentry/fs"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/kernel/signalfd"
+	"gvisor.dev/gvisor/pkg/sentry/usermem"
 	"gvisor.dev/gvisor/pkg/syserror"
 )
 
@@ -506,3 +509,77 @@ func RestartSyscall(t *kernel.Task, args arch.SyscallArguments) (uintptr, *kerne
 	t.Debugf("Restart block missing in restart_syscall(2). Did ptrace inject a return value of ERESTART_RESTARTBLOCK?")
 	return 0, nil, syserror.EINTR
 }
+
+// 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)
+	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.GetFile(fd)
+		if file == nil {
+			return 0, nil, syserror.EBADF
+		}
+		defer file.DecRef()
+
+		// Is this a signalfd?
+		if s, ok := file.FileOperations.(*signalfd.SignalOperations); ok {
+			s.SetMask(mask)
+			return 0, nil, nil
+		}
+
+		// Not a signalfd.
+		return 0, nil, syserror.EINVAL
+	}
+
+	// Create a new file.
+	file, err := signalfd.New(t, mask)
+	if err != nil {
+		return 0, nil, err
+	}
+	defer file.DecRef()
+
+	// Set appropriate flags.
+	file.SetFlags(fs.SettableFileFlags{
+		NonBlocking: flags&linux.SFD_NONBLOCK != 0,
+	})
+
+	// Create a new descriptor.
+	fd, err = t.NewFDFrom(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)
+}