RE: [PATCH 5/8] ima: allocate and initialize tfm for each PCR bank

Roberto Sassu
2020-01-31T13:42:18Z

> -----Original Message-----
> From: linux-integrity-owner@vger.kernel.org [mailto:linux-integrity-
> owner@vger.kernel.org] On Behalf Of Mimi Zohar
> Sent: Friday, January 31, 2020 1:19 PM
> To: Roberto Sassu <roberto.sassu@huawei.com>;
> jarkko.sakkinen@linux.intel.com;
> james.bottomley@hansenpartnership.com; linux-integrity@vger.kernel.org
> Cc: linux-security-module@vger.kernel.org; linux-kernel@vger.kernel.org;
> Silviu Vlasceanu <Silviu.Vlasceanu@huawei.com>
> Subject: Re: [PATCH 5/8] ima: allocate and initialize tfm for each PCR bank
>
> On Mon, 2020-01-27 at 18:04 +0100, Roberto Sassu wrote:
> > This patch creates a crypto_shash structure for each allocated PCR bank
> and
> > for SHA1 if a bank with that algorithm is not currently allocated.
> >
> > Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
>
> <snip>
>
> > +int __init ima_init_crypto(void)
> > +{
> > + enum hash_algo algo;
> > + long rc;
> > + int i;
> > +
> > + rc = ima_init_ima_crypto();
> > + if (rc)
> > + return rc;
> > +
> > + ima_algo_array = kmalloc_array(ima_tpm_chip-
> >nr_allocated_banks + 1,
> > + sizeof(*ima_algo_array), GFP_KERNEL);
>
> Perhaps instead of hard coding "nr_allocated_banks + 1", create a
> variable for storing the number of "extra" banks.  Walk the banks
> setting ima_sha1_idx and, later, in a subsequent patch set
> ima_hash_algo_idx.

I could store the indexes in an array and add ARRAY_SIZE of that array.

> > + if (!ima_algo_array) {
> > + rc = -ENOMEM;
> > + goto out;
> > + }
> > +
> > + for (i = 0; i < ima_tpm_chip->nr_allocated_banks + 1; i++) {
> > + ima_algo_array[i].tfm = NULL;
> > + ima_algo_array[i].algo = HASH_ALGO__LAST;
> > + }
>
> ima_init_crypto() is executed once on initialization.  I'm not sure if
> it makes a difference, but if you're really concerned about an
> additional loop, the initialization, here, could be limited to the
> "extra" banks.  The other banks could be initialized at the beginning
> of the next loop.

I set algo to HASH_ALGO__LAST to mark the ima_algo_array entries as
uninitialized. ima_alloc_tfm() uses ima_algo_array in the next loop.
Replacing kmalloc_array() with kcalloc() would cause algo to be set to
HASH_ALGO_MD4.

I could check tfm first, which ensures that also algo was initialized.

Roberto

> > + ima_sha1_idx = -1;
> > +
> > + for (i = 0; i < ima_tpm_chip->nr_allocated_banks; i++) {
> > + algo = ima_tpm_chip->allocated_banks[i].crypto_id;
> > + ima_algo_array[i].algo = algo;
> > +
> > + /* unknown TPM algorithm */
> > + if (algo == HASH_ALGO__LAST)
> > + continue;
> > +
> > + if (algo == HASH_ALGO_SHA1)
> > + ima_sha1_idx = i;
> > +
> > + if (algo == ima_hash_algo) {
> > + ima_algo_array[i].tfm = ima_shash_tfm;
> > + continue;
> > + }
> > +
> > + ima_algo_array[i].tfm = ima_alloc_tfm(algo);
> > + if (IS_ERR(ima_algo_array[i].tfm)) {
> > + if (algo == HASH_ALGO_SHA1) {
> > + rc = PTR_ERR(ima_algo_array[i].tfm);
> > + ima_algo_array[i].tfm = NULL;
> > + goto out_array;
> > + }
> > +
> > + ima_algo_array[i].tfm = NULL;
> > + }
> > + }
> > +
> > + if (ima_sha1_idx < 0) {
> > + ima_algo_array[i].tfm = ima_alloc_tfm(HASH_ALGO_SHA1);
> > + if (IS_ERR(ima_algo_array[i].tfm)) {
> > + rc = PTR_ERR(ima_algo_array[i].tfm);
> > + goto out_array;
> > + }
> > +
> > + ima_sha1_idx = i;
> > + ima_algo_array[i].algo = HASH_ALGO_SHA1;
> > + }
> > +
> > + return 0;
> > +out_array:
> > + for (i = 0; i < ima_tpm_chip->nr_allocated_banks + 1; i++) {
> > + if (!ima_algo_array[i].tfm ||
> > + ima_algo_array[i].tfm == ima_shash_tfm)
> > + continue;
> > +
> > + crypto_free_shash(ima_algo_array[i].tfm);
> > + }
> > +out:
> > + crypto_free_shash(ima_shash_tfm);
> > + return rc;
> > +}