diff --git a/solver/llbsolver/file/backend.go b/solver/llbsolver/file/backend.go
index 974c2e04e8773..d4a0b24c7087c 100644
--- a/solver/llbsolver/file/backend.go
+++ b/solver/llbsolver/file/backend.go
@@ -10,6 +10,7 @@ import (
 
 	"github.com/containerd/continuity/fs"
 	"github.com/docker/docker/pkg/idtools"
+	"github.com/moby/buildkit/executor"
 	"github.com/moby/buildkit/snapshot"
 	"github.com/moby/buildkit/solver/llbsolver/ops/fileoptypes"
 	"github.com/moby/buildkit/solver/pb"
@@ -25,46 +26,6 @@ func timestampToTime(ts int64) *time.Time {
 	return &tm
 }
 
-func mapUserToChowner(user *copy.User, idmap *idtools.IdentityMapping) (copy.Chowner, error) {
-	if user == nil {
-		return func(old *copy.User) (*copy.User, error) {
-			if old == nil {
-				if idmap == nil {
-					return nil, nil
-				}
-				old = &copy.User{} // root
-				// non-nil old is already mapped
-				if idmap != nil {
-					identity, err := idmap.ToHost(idtools.Identity{
-						UID: old.UID,
-						GID: old.GID,
-					})
-					if err != nil {
-						return nil, err
-					}
-					return &copy.User{UID: identity.UID, GID: identity.GID}, nil
-				}
-			}
-			return old, nil
-		}, nil
-	}
-	u := *user
-	if idmap != nil {
-		identity, err := idmap.ToHost(idtools.Identity{
-			UID: user.UID,
-			GID: user.GID,
-		})
-		if err != nil {
-			return nil, err
-		}
-		u.UID = identity.UID
-		u.GID = identity.GID
-	}
-	return func(*copy.User) (*copy.User, error) {
-		return &u, nil
-	}, nil
-}
-
 func mkdir(ctx context.Context, d string, action pb.FileActionMkDir, user *copy.User, idmap *idtools.IdentityMapping) error {
 	p, err := fs.RootPath(d, filepath.Join("/", action.Path))
 	if err != nil {
@@ -258,6 +219,7 @@ func cleanPath(s string) string {
 }
 
 type Backend struct {
+	Executor executor.Executor
 }
 
 func (fb *Backend) Mkdir(ctx context.Context, m, user, group fileoptypes.Mount, action pb.FileActionMkDir) error {
@@ -273,7 +235,7 @@ func (fb *Backend) Mkdir(ctx context.Context, m, user, group fileoptypes.Mount,
 	}
 	defer lm.Unmount()
 
-	u, err := readUser(action.Owner, user, group)
+	u, err := readUser(action.Owner, user, group, fb.Executor)
 	if err != nil {
 		return err
 	}
@@ -294,7 +256,7 @@ func (fb *Backend) Mkfile(ctx context.Context, m, user, group fileoptypes.Mount,
 	}
 	defer lm.Unmount()
 
-	u, err := readUser(action.Owner, user, group)
+	u, err := readUser(action.Owner, user, group, fb.Executor)
 	if err != nil {
 		return err
 	}
@@ -342,7 +304,7 @@ func (fb *Backend) Copy(ctx context.Context, m1, m2, user, group fileoptypes.Mou
 	}
 	defer lm2.Unmount()
 
-	u, err := readUser(action.Owner, user, group)
+	u, err := readUser(action.Owner, user, group, fb.Executor)
 	if err != nil {
 		return err
 	}
diff --git a/solver/llbsolver/file/backend_unix.go b/solver/llbsolver/file/backend_unix.go
new file mode 100644
index 0000000000000..d01290f300ace
--- /dev/null
+++ b/solver/llbsolver/file/backend_unix.go
@@ -0,0 +1,49 @@
+//go:build !windows
+// +build !windows
+
+package file
+
+import (
+	"github.com/docker/docker/pkg/idtools"
+	copy "github.com/tonistiigi/fsutil/copy"
+)
+
+func mapUserToChowner(user *copy.User, idmap *idtools.IdentityMapping) (copy.Chowner, error) {
+	if user == nil {
+		return func(old *copy.User) (*copy.User, error) {
+			if old == nil {
+				if idmap == nil {
+					return nil, nil
+				}
+				old = &copy.User{} // root
+				// non-nil old is already mapped
+				if idmap != nil {
+					identity, err := idmap.ToHost(idtools.Identity{
+						UID: old.UID,
+						GID: old.GID,
+					})
+					if err != nil {
+						return nil, err
+					}
+					return &copy.User{UID: identity.UID, GID: identity.GID}, nil
+				}
+			}
+			return old, nil
+		}, nil
+	}
+	u := *user
+	if idmap != nil {
+		identity, err := idmap.ToHost(idtools.Identity{
+			UID: user.UID,
+			GID: user.GID,
+		})
+		if err != nil {
+			return nil, err
+		}
+		u.UID = identity.UID
+		u.GID = identity.GID
+	}
+	return func(*copy.User) (*copy.User, error) {
+		return &u, nil
+	}, nil
+}
diff --git a/solver/llbsolver/file/backend_windows.go b/solver/llbsolver/file/backend_windows.go
new file mode 100644
index 0000000000000..03f3bbe7b3089
--- /dev/null
+++ b/solver/llbsolver/file/backend_windows.go
@@ -0,0 +1,22 @@
+package file
+
+import (
+	"github.com/docker/docker/pkg/idtools"
+	copy "github.com/tonistiigi/fsutil/copy"
+)
+
+func mapUserToChowner(user *copy.User, idmap *idtools.IdentityMapping) (copy.Chowner, error) {
+	if user == nil || user.SID == "" {
+		return func(old *copy.User) (*copy.User, error) {
+			if old == nil || old.SID == "" {
+				old = &copy.User{
+					SID: idtools.ContainerAdministratorSidString,
+				}
+			}
+			return old, nil
+		}, nil
+	}
+	return func(*copy.User) (*copy.User, error) {
+		return user, nil
+	}, nil
+}
diff --git a/solver/llbsolver/file/user_linux.go b/solver/llbsolver/file/user_linux.go
index 1f17431f5c326..2871db9b0d1a9 100644
--- a/solver/llbsolver/file/user_linux.go
+++ b/solver/llbsolver/file/user_linux.go
@@ -13,7 +13,7 @@ import (
 	copy "github.com/tonistiigi/fsutil/copy"
 )
 
-func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
+func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount, exec executor.Executor) (*copy.User, error) {
 	if chopt == nil {
 		return nil, nil
 	}
diff --git a/solver/llbsolver/file/user_nolinux.go b/solver/llbsolver/file/user_other.go
similarity index 50%
rename from solver/llbsolver/file/user_nolinux.go
rename to solver/llbsolver/file/user_other.go
index 80652fd4abe4b..1a81984a6afdd 100644
--- a/solver/llbsolver/file/user_nolinux.go
+++ b/solver/llbsolver/file/user_other.go
@@ -1,5 +1,5 @@
-//go:build !linux
-// +build !linux
+//go:build !linux && !windows
+// +build !linux,!windows
 
 package file
 
@@ -10,9 +10,9 @@ import (
 	copy "github.com/tonistiigi/fsutil/copy"
 )
 
-func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount) (*copy.User, error) {
+func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount, exec executor.Executor) (*copy.User, error) {
 	if chopt == nil {
 		return nil, nil
 	}
-	return nil, errors.New("only implemented in linux")
+	return nil, errors.New("only implemented in linux and windows")
 }
diff --git a/solver/llbsolver/file/user_windows.go b/solver/llbsolver/file/user_windows.go
new file mode 100644
index 0000000000000..06e160e7085da
--- /dev/null
+++ b/solver/llbsolver/file/user_windows.go
@@ -0,0 +1,41 @@
+package file
+
+import (
+	"context"
+
+	"github.com/docker/docker/pkg/idtools"
+	"github.com/moby/buildkit/executor"
+	"github.com/moby/buildkit/solver/llbsolver/ops/fileoptypes"
+	"github.com/moby/buildkit/solver/pb"
+	"github.com/moby/buildkit/util/windows"
+	"github.com/pkg/errors"
+	copy "github.com/tonistiigi/fsutil/copy"
+)
+
+func readUser(chopt *pb.ChownOpt, mu, mg fileoptypes.Mount, exec executor.Executor) (*copy.User, error) {
+	if chopt == nil {
+		return nil, nil
+	}
+
+	if chopt.User != nil {
+		switch u := chopt.User.User.(type) {
+		case *pb.UserOpt_ByName:
+			if mu == nil {
+				return nil, errors.Errorf("invalid missing user mount")
+			}
+			mmu, ok := mu.(*Mount)
+			if !ok {
+				return nil, errors.Errorf("invalid mount type %T", mu)
+			}
+
+			ident, err := windows.ResolveUsernameToSID(context.Background(), exec, mmu.m, u.ByName.Name)
+			if err != nil {
+				return nil, err
+			}
+			return &copy.User{SID: ident.SID}, nil
+		default:
+			return &copy.User{SID: idtools.ContainerAdministratorSidString}, nil
+		}
+	}
+	return &copy.User{SID: idtools.ContainerAdministratorSidString}, nil
+}
diff --git a/solver/llbsolver/ops/file.go b/solver/llbsolver/ops/file.go
index 7bbb3276797cd..f3225e45e2c2c 100644
--- a/solver/llbsolver/ops/file.go
+++ b/solver/llbsolver/ops/file.go
@@ -46,7 +46,7 @@ func NewFileOp(v solver.Vertex, op *pb.Op_File, cm cache.Manager, parallelism *s
 		md:          cm,
 		numInputs:   len(v.Inputs()),
 		w:           w,
-		solver:      NewFileOpSolver(w, &file.Backend{}, file.NewRefManager(cm, v.Name())),
+		solver:      NewFileOpSolver(w, &file.Backend{Executor: w.Executor()}, file.NewRefManager(cm, v.Name())),
 		parallelism: parallelism,
 	}, nil
 }