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Subject: Re: [PATCH 2/2] SELinux: Measure state and hash of policy using IMA
To:     Stephen Smalley <stephen.smalley.work@gmail.com>
Cc:     Mimi Zohar <zohar@linux.ibm.com>,
        Casey Schaufler <casey@schaufler-ca.com>,
        Tyler Hicks <tyhicks@linux.microsoft.com>,
        tusharsu@linux.microsoft.com, sashal@kernel.org,
        James Morris <jmorris@namei.org>,
        linux-integrity@vger.kernel.org,
        SElinux list <selinux@vger.kernel.org>,
        LSM List <linux-security-module@vger.kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        paul Moore <paul@paul-moore.com>
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 <CAEjxPJ6sZdm2w=bbkL0uJyEkHw0gCT_y812WQBZPtLCJzO6r3A@mail.gmail.com>
From:   Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Message-ID: <e935c06f-09e2-a2f7-f97f-768bc017f477@linux.microsoft.com>
Date:   Thu, 13 Aug 2020 11:03:04 -0700
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On 8/13/20 10:58 AM, Stephen Smalley wrote:
> On Thu, Aug 13, 2020 at 1:52 PM Lakshmi Ramasubramanian
> <nramas@linux.microsoft.com> wrote:
>>
>> On 8/13/20 10:42 AM, Stephen Smalley wrote:
>>
>>>> diff --git a/security/selinux/measure.c b/security/selinux/measure.c
>>>> new file mode 100644
>>>> index 000000000000..f21b7de4e2ae
>>>> --- /dev/null
>>>> +++ b/security/selinux/measure.c
>>>> @@ -0,0 +1,204 @@
>>>> +static int selinux_hash_buffer(void *buf, size_t buf_len,
>>>> +                   void **buf_hash, int *buf_hash_len)
>>>> +{
>>>> +    struct crypto_shash *tfm;
>>>> +    struct shash_desc *desc = NULL;
>>>> +    void *digest = NULL;
>>>> +    int desc_size;
>>>> +    int digest_size;
>>>> +    int ret = 0;
>>>> +
>>>> +    tfm = crypto_alloc_shash("sha256", 0, 0);
>>>> +    if (IS_ERR(tfm))
>>>> +        return PTR_ERR(tfm);
>>> Can we make the algorithm selectable via kernel parameter and/or writing
>>> to a new selinuxfs node?
>>
>> I can add a kernel parameter to select this hash algorithm.
> 
> Also can we provide a Kconfig option for the default value like IMA does?
> 

Would we need both - Kconfig and kernel param?

The other option is to provide an IMA function to return the current 
hash algorithm used for measurement. That way a consistent hash 
algorithm can be employed by both IMA and the callers. Would that be better?

  -lakshmi