Re: [PATCH 2/5] keys: generate self-signed module signing key using CSR

[Nayna]

On 2/11/21 5:01 PM, Stefan Berger wrote:
> On 2/11/21 2:54 PM, Nayna Jain wrote:
> > Loading a key on the IMA trusted keyring requires the key be signed
> > by an existing key on the builtin or secondary trusted keyring.
> > Creating a Certificate Signing Request (CSR) allows the certificate
> > to be self-signed or signed by a CA.
> >
> > This patch generates a self-signed module signing key using CSR.
> >
> > Signed-off-by: Nayna Jain <nayna@xxxxxxxxxxxxx>
> > ---
> >   Makefile       |  3 ++-
> >   certs/Makefile | 15 +++++++++++----
> >   2 files changed, 13 insertions(+), 5 deletions(-)
> >
> > diff --git a/Makefile b/Makefile
> > index af18aab6bbee..9c87fdd600d8 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -1473,7 +1473,8 @@ MRPROPER_FILES += include/config 
> > include/generated          \
> >             .config .config.old .version \
> >             Module.symvers \
> >             certs/signing_key.pem certs/signing_key.x509 \
> > -          certs/x509.genkey \
> > +          certs/x509.genkey certs/signing_key.key \
> > +          certs/signing_key.crt certs/signing_key.csr \
> >             vmlinux-gdb.py \
> >             *.spec
> >   diff --git a/certs/Makefile b/certs/Makefile
> > index f4c25b67aad9..b2be7eb413d3 100644
> > --- a/certs/Makefile
> > +++ b/certs/Makefile
> > @@ -60,11 +60,18 @@ $(obj)/signing_key.pem: $(obj)/x509.genkey
> >       @$(kecho) "### needs to be run as root, and uses a hardware 
> > random"
> >       @$(kecho) "### number generator if one is available."
> >       @$(kecho) "###"
> > -    $(Q)openssl req -new -nodes -utf8 -$(CONFIG_MODULE_SIG_HASH) 
> > -days 36500 \
> > -        -batch -x509 -config $(obj)/x509.genkey \
> > -        -outform PEM -out $(obj)/signing_key.pem \
> > -        -keyout $(obj)/signing_key.pem \
> > +    $(Q)openssl req -new -nodes -utf8 \
> > +        -batch -config $(obj)/x509.genkey \
> > +        -outform PEM -out $(obj)/signing_key.csr \
> > +        -keyout $(obj)/signing_key.key -extensions myexts \
> >           $($(quiet)redirect_openssl)
> > +    $(Q)openssl x509 -req -days 36500 -in $(obj)/signing_key.csr \
> > +        -outform PEM -out $(obj)/signing_key.crt \
> > +        -signkey $(obj)/signing_key.key \
> > +        -$(CONFIG_MODULE_SIG_HASH) -extensions myexts \
> > +        -extfile $(obj)/x509.genkey \
> > +        $($(quiet)redirect_openssl)
> > +    @cat $(obj)/signing_key.key $(obj)/signing_key.crt >> 
> > $(obj)/signing_key.pem
>
>
> Could you not just rename signing_key.key to signing_key.pem (as it 
> was before) and that would be it? Why do you need the .crt in that pem 
> bundle?

I had also thought so, but the PEM file contains both the private key 
and the certificate. I found the reasoning in the commit "fb1179499134 
modsign: Use single PEM file for autogenerated key". I addressed your 
other feedback in v2, posted just now.

Thanks & Regards,

      - Nayna