Add vanilla Linux kernel build

Currently we only build kernel with the dma patch. Some clients
use virtio 1.0 and they do not need this patch. To solve this we
want to build a vanilla kernel.

Change-Id: Ie624481827a4e74e761b530e6ce5e4dce8153509

flake.nix

@@ -34,7 +34,8 @@
           # reproducibility.
           # Note that building a package via nix is not by itself a guarantee of
           # reproducibility; see https://reproducible.nixos.org.
-          linux_kernel = pkgs.linuxManualConfig {
+          # Common kernel configuration
+          commonLinuxKernelConfig = {
             # To allow reproducibility, the following options need to be configured:
             # - CONFIG_MODULE_SIG is not set
             # - CONFIG_MODULE_SIG_ALL is not set
@@ -49,11 +50,16 @@
             version = linux_kernel_version;
             src = linux_kernel_src;
             allowImportFromDerivation = true;
+          };
+          # Patched kernel
+          linux_kernel = pkgs.linuxManualConfig (commonLinuxKernelConfig // {
             kernelPatches = [{
               name = "virtio-dma";
               patch = ./oak_containers_kernel/patches/virtio-dma.patch;
             }];
-          };
+          });
+          # Vanilla kernel
+          vanilla_linux_kernel = pkgs.linuxManualConfig commonLinuxKernelConfig;
           androidSdk =
             (pkgs.androidenv.composeAndroidPackages {
               platformVersions = [ "30" ];
@@ -101,7 +107,7 @@
           };
         in
         {
-          packages = { inherit linux_kernel; };
+          packages = { inherit linux_kernel; inherit vanilla_linux_kernel; };
           formatter = pkgs.nixpkgs-fmt;
           # We define a recursive set of shells, so that we can easily create a shell with a subset
           # of the dependencies for specific CI steps, without having to pull everything all the time.
@@ -184,6 +190,7 @@
             containers = with pkgs; mkShell {
               shellHook = ''
                 export LINUX_KERNEL="${linux_kernel}"
+                export VANILLA_LINUX_KERNEL="${vanilla_linux_kernel}"
               '';
               inputsFrom = [
                 base
@@ -214,6 +221,7 @@
             bzImageProvenance = with pkgs; mkShell {
               shellHook = ''
                 export LINUX_KERNEL="${linux_kernel}"
+                export VANILLA_LINUX_KERNEL="${vanilla_linux_kernel}"
               '';
               inputsFrom = [
                 rust