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

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Date:   Thu, 18 Feb 2021 17:02:53 -0500
From:   Nayna <nayna@...ux.vnet.ibm.com>
To:     Stefan Berger <stefanb@...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>,
        Nayna Jain <nayna@...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 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@...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?

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