neonvm: explicitly specify platform in FROM section of the kernel bui…

…lder image to have cp binary of the correct architecture

Signed-off-by: Misha Sakhnov <[email protected]>

neonvm/hack/kernel/Dockerfile.kernel-builder

@@ -60,7 +60,7 @@ RUN cd linux-${KERNEL_VERSION} && make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gn
 # Copy the kernel image to a separate step
 # Use alpine so that `cp` is available when loading custom kernels for the runner pod.
 # See the neonvm controller's pod creation logic for more detail.
-FROM alpine:3.19 AS kernel_amd64
+FROM --platform=linux/amd64 alpine:3.19 AS kernel_amd64
 ARG KERNEL_VERSION
 COPY --from=build_amd64 /build/linux-${KERNEL_VERSION}/arch/x86/boot/bzImage /vmlinuz
 
@@ -73,6 +73,6 @@ RUN cd linux-${KERNEL_VERSION} && make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gn
 # Copy the kernel image to a separate step
 # Use alpine so that `cp` is available when loading custom kernels for the runner pod.
 # See the neonvm controller's pod creation logic for more detail.
-FROM alpine:3.19 AS kernel_arm64
+FROM --platform=linux/arm64 alpine:3.19 AS kernel_arm64
 ARG KERNEL_VERSION
 COPY --from=build_arm64 /build/linux-${KERNEL_VERSION}/arch/arm64/boot/Image /vmlinuz