mkDerivation, cc-wrapper: Check hardening flag validity in Nix

This becomes necessary if more wrappers besides cc-wrapper start
supporting hardening flags. Also good to make the warning into an
error.

Also ensure interface is being used right: Not as a string, not just in
bash.

pkgs/build-support/cc-wrapper/add-hardening.sh

@@ -68,7 +68,8 @@ if [[ -z "${hardeningDisableMap[all]:-}" ]]; then
           hardeningLDFlags+=('-z' 'now')
           ;;
         *)
-          echo "Hardening flag unknown: $flag" >&2
+          # Ignore unsupported. Checked in Nix that at least *some*
+          # tool supports each flag.
           ;;
       esac
     fi

pkgs/os-specific/linux/devmem2/default.nix

@@ -8,8 +8,9 @@ stdenv.mkDerivation rec {
     sha256 = "14f1k7v6i1yaxg4xcaaf5i4aqn0yabba857zjnbg9wiymy82qf7c";
   };
 
+  hardeningDisable = [ "format" ];  # fix compile error
+
   buildCommand = ''
-    export hardeningDisable=format  # fix compile error
     cc "$src" -o devmem2
     install -D devmem2 "$out/bin/devmem2"
   '';

pkgs/os-specific/linux/firmware/fwupdate/default.nix

@@ -17,7 +17,7 @@ let version = "8"; in
       buildInputs = [ gnu-efi libsmbios popt pkgconfig gettext ];
       propagatedBuildInputs = [ efivar ];
       # TODO: Just apply the disable to the efi subdir
-      hardeningDisable = "all";
+      hardeningDisable = [ "all" ];
       patchPhase = ''
         sed -i 's|/usr/include/smbios_c/token.h|smbios_c/token.h|' \
           linux/libfwup.c

pkgs/stdenv/generic/make-derivation.nix

@@ -41,7 +41,20 @@ rec {
     , __propagatedImpureHostDeps ? []
     , sandboxProfile ? ""
     , propagatedSandboxProfile ? ""
+
+    , hardeningEnable ? []
+    , hardeningDisable ? []
     , ... } @ attrs:
+
+    # TODO(@Ericson2314): Make this more modular, and not O(n^2).
+    let allHardeningFlags = [
+      "fortify" "stackprotector" "pie" "pic" "strictoverflow" "format" "relro"
+      "bindnow"
+    ];
+    in assert lib.all
+      (flag: lib.elem flag allHardeningFlags)
+      (hardeningEnable ++ hardeningDisable);
+
     let
       dependencies = map lib.chooseDevOutputs [
         (map (drv: drv.nativeDrv or drv) nativeBuildInputs

pkgs/tools/networking/envoy/default.nix

@@ -233,7 +233,7 @@ stdenv.mkDerivation rec {
 
   patches = [ ./nixos.patch ];
 
-  hardeningDisable = "all";
+  hardeningDisable = [ "all" ];
   dontPatchELF = true;
   dontStrip = true;