RE: [PATCH v2 5/8] ima: Switch to dynamically allocated buffer for template digests

[Roberto Sassu <roberto.sassu@huawei.com>]

> -----Original Message-----
> From: owner-linux-security-module@vger.kernel.org [mailto:owner-linux-
> security-module@vger.kernel.org] On Behalf Of Mimi Zohar
> Sent: Thursday, February 6, 2020 5:34 PM
> To: Roberto Sassu <roberto.sassu@huawei.com>;
> James.Bottomley@HansenPartnership.com;
> jarkko.sakkinen@linux.intel.com
> Cc: linux-integrity@vger.kernel.org; linux-security-module@vger.kernel.org;
> linux-kernel@vger.kernel.org; Silviu Vlasceanu
> <Silviu.Vlasceanu@huawei.com>
> Subject: Re: [PATCH v2 5/8] ima: Switch to dynamically allocated buffer for
> template digests
> 
> On Thu, 2020-02-06 at 16:27 +0000, Roberto Sassu wrote:
> > > -----Original Message-----
> > > From: Mimi Zohar [mailto:zohar@linux.ibm.com]
> > > Sent: Thursday, February 6, 2020 5:08 PM
> > > To: Roberto Sassu <roberto.sassu@huawei.com>;
> > > James.Bottomley@HansenPartnership.com;
> > > jarkko.sakkinen@linux.intel.com
> > > Cc: linux-integrity@vger.kernel.org; linux-security-
> module@vger.kernel.org;
> > > linux-kernel@vger.kernel.org; Silviu Vlasceanu
> > > <Silviu.Vlasceanu@huawei.com>
> > > Subject: Re: [PATCH v2 5/8] ima: Switch to dynamically allocated buffer
> for
> > > template digests
> > >
> > > Hi Roberto,
> > >
> > > On Wed, 2020-02-05 at 11:33 +0100, Roberto Sassu wrote:
> > > > This patch dynamically allocates the array of tpm_digest structures in
> > > > ima_alloc_init_template() and ima_restore_template_data(). The size
> of
> > > the
> > > > array, stored in ima_num_template_digests, is initially equal to 1
> (SHA1)
> > > > and will be determined in the upcoming patches depending on the
> > > allocated
> > > > PCR banks and the chosen default IMA algorithm.
> > > >
> > > > Calculating the SHA1 digest is mandatory, as SHA1 still remains the
> default
> > > > hash algorithm for the measurement list. When IMA will support the
> > > Crypto
> > > > Agile format, remaining digests will be also provided.
> > > >
> > > > The position in the array of the SHA1 digest is stored in the
> ima_sha1_idx
> > > > global variable and it is determined at IMA initialization time.
> > > >
> > > > Changelog
> > > >
> > > > v1:
> > > > - move ima_sha1_idx to ima_crypto.c
> > > > - introduce ima_num_template_digests (suggested by Mimi)
> > >
> > > Instead of hardcoding "nr_allocated_banks + 1" or nr_allocated_banks +
> > > 2", I suggested defining "nr_allocated_banks + extra", where "extra"
> > > could be 0, 1, or 2.
> > >
> > > The rest of the code would remain exactly the same as you had.
> >
> > Ok. I did a small improvement. Since we determine the number of
> > required elements of ima_algo_array before kmalloc() I thought it
> > was ok to directly set that number of elements in a single variable.
> >
> > If you think that having two variables is better, I will change it.
> 
> The connection to nr_allocated_banks is then not as visible.  Using
> two variables is clearer.

Ok, no problem. I will change it in the next version.

Roberto

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