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

[Georgy Yakovlev]

On Sun, 2022-06-26 at 03:52 -0700, Georgy Yakovlev wrote:
> 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.

after reading my old code again and thinking more I think I know what's
going on.
 1. I've actually solved checksum/strip problem by signing in pkg-
preinst
 2. my method will likely fail with compressed modules.
 3. your method likely works only if modules are compressed - because
portage does not strip those I think.

so looks like we need to combine both methods and do the following:
 - if signing requested without compression - sign in pkg_preinst.
 - if signing requested with compression - sign in src_install

Do I make sense? I still haven't tested it, just guessing as I read my
old bash code.