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

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Message-ID: <c9e509fb-59df-28b4-654c-543cd922239c@linux.ibm.com>
Date:   Thu, 11 Feb 2021 17:01:15 -0500
From:   Stefan Berger <stefanb@...ux.ibm.com>
To:     Nayna Jain <nayna@...ux.ibm.com>, linux-integrity@...r.kernel.org,
        keyrings@...r.kernel.org
Cc:     linux-security-module@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/5] keys: generate self-signed module signing key using
 CSR

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@...ux.ibm.com>
> ---
>   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?

    Stefan