diff --git a/osbase/build/kconfig-patcher/BUILD.bazel b/osbase/build/kconfig-patcher/BUILD.bazel
new file mode 100644
index 0000000..59ee391
--- /dev/null
+++ b/osbase/build/kconfig-patcher/BUILD.bazel
@@ -0,0 +1,23 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library", "go_test")
+
+go_library(
+    name = "kconfig-patcher_lib",
+    srcs = ["main.go"],
+    importpath = "source.monogon.dev/osbase/build/kconfig-patcher",
+    visibility = ["//visibility:private"],
+)
+
+go_binary(
+    name = "kconfig-patcher",
+    embed = [":kconfig-patcher_lib"],
+    visibility = [
+        "//metropolis/node:__pkg__",
+        "//osbase/test/ktest:__pkg__",
+    ],
+)
+
+go_test(
+    name = "kconfig-patcher_test",
+    srcs = ["main_test.go"],
+    embed = [":kconfig-patcher_lib"],
+)
diff --git a/osbase/build/kconfig-patcher/kconfig-patcher.bzl b/osbase/build/kconfig-patcher/kconfig-patcher.bzl
new file mode 100644
index 0000000..39e786e
--- /dev/null
+++ b/osbase/build/kconfig-patcher/kconfig-patcher.bzl
@@ -0,0 +1,33 @@
+#  Copyright 2020 The Monogon Project Authors.
+#
+#  SPDX-License-Identifier: Apache-2.0
+#
+#  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.
+
+"""Override configs in a Linux kernel Kconfig
+"""
+
+def kconfig_patch(name, src, out, override_configs, **kwargs):
+    native.genrule(
+        name = name,
+        srcs = [src],
+        outs = [out],
+        tools = [
+            "//osbase/build/kconfig-patcher",
+        ],
+        cmd = """
+        $(location //osbase/build/kconfig-patcher) \
+            -in $< -out $@ '%s'
+        """ % struct(overrides = override_configs).to_json(),
+        **kwargs
+    )
diff --git a/osbase/build/kconfig-patcher/main.go b/osbase/build/kconfig-patcher/main.go
new file mode 100644
index 0000000..1b5f24f
--- /dev/null
+++ b/osbase/build/kconfig-patcher/main.go
@@ -0,0 +1,98 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// 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 main
+
+import (
+	"bufio"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+)
+
+var (
+	inPath  = flag.String("in", "", "Path to input Kconfig")
+	outPath = flag.String("out", "", "Path to output Kconfig")
+)
+
+func main() {
+	flag.Parse()
+	if *inPath == "" || *outPath == "" {
+		flag.PrintDefaults()
+		os.Exit(2)
+	}
+	inFile, err := os.Open(*inPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to open input Kconfig: %v\n", err)
+		os.Exit(1)
+	}
+	outFile, err := os.Create(*outPath)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to create output Kconfig: %v\n", err)
+		os.Exit(1)
+	}
+	var config struct {
+		Overrides map[string]string `json:"overrides"`
+	}
+	if err := json.Unmarshal([]byte(flag.Arg(0)), &config); err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to parse overrides: %v\n", err)
+		os.Exit(1)
+	}
+	err = patchKconfig(inFile, outFile, config.Overrides)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "Failed to patch: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func patchKconfig(inFile io.Reader, outFile io.Writer, overrides map[string]string) error {
+	scanner := bufio.NewScanner(inFile)
+	for scanner.Scan() {
+		if scanner.Err() != nil {
+			return scanner.Err()
+		}
+		line := scanner.Text()
+		cleanLine := strings.TrimSpace(line)
+		if strings.HasPrefix(cleanLine, "#") || cleanLine == "" {
+			// Pass through comments and empty lines
+			fmt.Fprintln(outFile, line)
+		} else {
+			// Line contains a configuration option
+			parts := strings.SplitN(line, "=", 2)
+			keyName := parts[0]
+			if overrideVal, ok := overrides[strings.TrimSpace(keyName)]; ok {
+				// Override it
+				if overrideVal == "" {
+					fmt.Fprintf(outFile, "# %v is not set\n", keyName)
+				} else {
+					fmt.Fprintf(outFile, "%v=%v\n", keyName, overrideVal)
+				}
+				delete(overrides, keyName)
+			} else {
+				// Pass through unchanged
+				fmt.Fprintln(outFile, line)
+			}
+		}
+	}
+	// Process left over overrides
+	for key, val := range overrides {
+		fmt.Fprintf(outFile, "%v=%v\n", key, val)
+	}
+	return nil
+}
diff --git a/osbase/build/kconfig-patcher/main_test.go b/osbase/build/kconfig-patcher/main_test.go
new file mode 100644
index 0000000..11c7d84
--- /dev/null
+++ b/osbase/build/kconfig-patcher/main_test.go
@@ -0,0 +1,61 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// 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 main
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func Test_patchKconfig(t *testing.T) {
+	type args struct {
+		inFile    string
+		overrides map[string]string
+	}
+	tests := []struct {
+		name        string
+		args        args
+		wantOutFile string
+		wantErr     bool
+	}{
+		{
+			"passthroughExtend",
+			args{inFile: "# TEST=y\n\n", overrides: map[string]string{"TEST": "n"}},
+			"# TEST=y\n\nTEST=n\n",
+			false,
+		},
+		{
+			"patch",
+			args{inFile: "TEST=y\nTEST_NO=n\n", overrides: map[string]string{"TEST": "n"}},
+			"TEST=n\nTEST_NO=n\n",
+			false,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			outFile := &bytes.Buffer{}
+			if err := patchKconfig(strings.NewReader(tt.args.inFile), outFile, tt.args.overrides); (err != nil) != tt.wantErr {
+				t.Errorf("patchKconfig() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if gotOutFile := outFile.String(); gotOutFile != tt.wantOutFile {
+				t.Errorf("patchKconfig() = %v, want %v", gotOutFile, tt.wantOutFile)
+			}
+		})
+	}
+}