Re: [gentoo-dev] [PATCH] linux-mod.eclass: support module signing

[Georgy Yakovlev]

On Tue, 2022-06-21 at 14:19 -0400, Kenton Groombridge wrote:
> eee74b9fca1 adds support for module compression, but this breaks
> loading
> out of tree modules when module signing is enforced because modules
> must
> be signed before they are compressed. Additionally, the recommended
> Portage hook[1] no longer works with this change.
>
> Add module signing support in linux-mod.eclass which more or less
> does
> exactly what the aforementioned Portage hook does. If the kernel
> configuration has CONFIG_MODULE_SIG_ALL=y, then read the hash and
> keys
> from the kernel configuration and call the sign_file tool to sign the
> module before it is compressed.
>
> Bug: https://bugs.gentoo.org/show_bug.cgi?id=447352
> Signed-off-by: Kenton Groombridge <concord@g.o>
> ---
>  eclass/linux-mod.eclass | 16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
>
> diff --git a/eclass/linux-mod.eclass b/eclass/linux-mod.eclass
> index b7c13cbf7e7..fd40f6d7c6c 100644
> --- a/eclass/linux-mod.eclass
> +++ b/eclass/linux-mod.eclass
> @@ -712,6 +712,22 @@ linux-mod_src_install() {
>                 cd "${objdir}" || die "${objdir} does not exist"
>                 insinto
> "${INSTALL_MOD_PATH}"/lib/modules/${KV_FULL}/${libdir}
>  
> +               # check here for CONFIG_MODULE_SIG_ALL and sign the
> module being built if enabled.
> +               # modules must be signed before they are compressed.
> +
> +               if linux_chkconfig_present MODULE_SIG_ALL; then
> +                       local
> module_sig_hash="$(linux_chkconfig_string MODULE_SIG_HASH)"
> +                       local
> module_sig_key="$(linux_chkconfig_string MODULE_SIG_KEY)"
> +                       module_sig_key="${module_sig_key:-
> certs/signing_key.pem}"
> +                       if [[ "${module_sig_key#pkcs11:}" ==
> "${module_sig_key}" && "${module_sig_key#/}" == "${module_sig_key}"
> ]]; then
> +                               local
> key_path="${KERNEL_DIR}/${module_sig_key}"
> +                       else
> +                               local key_path="${module_sig_key}"
> +                       fi
> +                       local
> cert_path="${KERNEL_DIR}/certs/signing_key.x509"
> +                       "${KERNEL_DIR}"/scripts/sign-file
> ${module_sig_hash//\"} ${key_path//\"} ${cert_path}
> ${modulename}.${KV_OBJ}
> +               fi
> +
>                 # check here for CONFIG_MODULE_COMPRESS_<compression
> option> (NONE, GZIP, XZ, ZSTD)
>                 # and similarily compress the module being built if
> != NONE.
>  


Hi,

I've spent some time in the past ( circa 2018 ) to get this in, but 
gave up due to various reasons, I was not a gentoo dev yet at the time.

I can't see how posted implementation will work tbh.
portage will strip signature out of the module, unless you prevent
stripping completely or package uses EAPI>=7, and omits stripping
modules via dostrip -x on the ko object.
kernel will NOT load module with stripped signature.

so either you have to sign in pkg_postinst phase, or prevent stripping.
signing in postinst is not ideal, because if breaks recorded file
checksums in vdb.

here's old fork of eclass I made, maybe you can find some helpful code
in there

https://github.com/gyakovlev/linux-mod.eclass/blob/master/linux-mod.eclass

old ML discussion we had:
https://archives.gentoo.org/gentoo-dev/message/4b15b1c851f379a1f802e2f2895cdfa8

You will also need a dependency on openssl, since sign-file uses it.

lmk if you need more info, I might remember more details, but for now
that's all I have. I'll try to help get it done, but my availability is
spotty due to limited time.