Re: [PATCH v2 1/3] ima: use ahash API for file hash calculation

[Dmitry Kasatkin]

On 2 July 2014 19:40, Mimi Zohar <zohar@xxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 2014-07-01 at 23:12 +0300, Dmitry Kasatkin wrote:
>> Async hash API allows to use HW acceleration for hash calculation.
>> It may give significant performance gain or/and reduce power consumption,
>> which might be very beneficial for battery powered devices.
>>
>> This patch introduces hash calculation using ahash API.
>>
>> ahash performance depends on data size and particular HW. Under certain
>> limit, depending on the system, shash performance may be better.
>>
>> This patch defines 'ima_ahash' kernel parameter which can be used to
>> define minimal file size to use with ahash. When file size is not set
>> or smaller than defined by the parameter, shash will be used.
>
> Thank you for the updated patches. The changes should be listed here in
> the patch description.
>
> I keep going back and forth as to whether the ahash routines should be
> totally separate, as posted, from the shash routines.  Having separate
> functions is very clear/clean, but there is quite a bit of code
> duplication (eg. ima_calc_file_hash()/ima_calc_file_ahash(),
> ima_free_tfm()/ima_free_atfm(), ima_alloc_tfm()/ima_alloc_atfm()).
>
> Soliciting comments ...
>

I think what you say is a "pattern": alloc/calc/free.
But the code uses different API mostly and there very small duplication...

In fact with this 'clean' separation we can have CONFIG_ option to
ifdef the code ot have it in separate file for those who really want
to make smallest kernel possible...


>> Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
>
>> ---
>>  Documentation/kernel-parameters.txt |   5 +
>>  security/integrity/ima/ima_crypto.c | 185 +++++++++++++++++++++++++++++++++++-
>>  2 files changed, 186 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
>> index 5a214a3..b406f5c 100644
>> --- a/Documentation/kernel-parameters.txt
>> +++ b/Documentation/kernel-parameters.txt
>> @@ -1291,6 +1291,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>>       ihash_entries=  [KNL]
>>                       Set number of hash buckets for inode cache.
>>
>> +     ima_ahash=      [IMA] Asynchronous hash usage parameters
>> +                     Format: <min_file_size>
>> +                     Set the minimal file size when use asynchronous hash.
>> +                     If ima_ahash is not provided, ahash usage is disabled.
>> +
>>       ima_appraise=   [IMA] appraise integrity measurements
>>                       Format: { "off" | "enforce" | "fix" }
>>                       default: "enforce"
>> diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
>> index f82d1d7..5eb19b4 100644
>> --- a/security/integrity/ima/ima_crypto.c
>> +++ b/security/integrity/ima/ima_crypto.c
>> @@ -25,7 +25,27 @@
>>  #include <crypto/hash_info.h>
>>  #include "ima.h"
>>
>> +
>
> Extra blank line not needed.
>
>> +struct ahash_completion {
>> +     struct completion completion;
>> +     int err;
>> +};
>> +
>>  static struct crypto_shash *ima_shash_tfm;
>> +static struct crypto_ahash *ima_ahash_tfm;
>> +
>> +/* minimal file size for ahash use */
>> +static loff_t ima_ahash_size;
>> +
>> +static int __init ima_ahash_setup(char *str)
>> +{
>> +     int rc;
>> +
>> +     rc = kstrtoll(str, 10, &ima_ahash_size);
>> +
>> +     return !rc;
>> +}
>> +__setup("ima_ahash=", ima_ahash_setup);
>>
>>  /**
>>   * ima_kernel_read - read file content
>> @@ -93,9 +113,146 @@ static void ima_free_tfm(struct crypto_shash *tfm)
>>               crypto_free_shash(tfm);
>>  }
>>
>> -/*
>> - * Calculate the MD5/SHA1 file digest
>> - */
>> +static struct crypto_ahash *ima_alloc_atfm(enum hash_algo algo)
>> +{
>> +     struct crypto_ahash *tfm = ima_ahash_tfm;
>> +     int rc;
>> +
>> +     if ((algo != ima_hash_algo && algo < HASH_ALGO__LAST) || !tfm) {
>> +             tfm = crypto_alloc_ahash(hash_algo_name[algo], 0, 0);
>> +             if (!IS_ERR(tfm)) {
>> +                     if (algo == ima_hash_algo)
>> +                             ima_ahash_tfm = tfm;
>> +             } else {
>> +                     rc = PTR_ERR(tfm);
>> +                     pr_err("Can not allocate %s (reason: %d)\n",
>> +                            hash_algo_name[algo], rc);
>> +             }
>> +     }
>> +     return tfm;
>> +}
>> +
>> +static void ima_free_atfm(struct crypto_ahash *tfm)
>> +{
>> +     if (tfm != ima_ahash_tfm)
>> +             crypto_free_ahash(tfm);
>> +}
>> +
>> +static void ahash_complete(struct crypto_async_request *req, int err)
>> +{
>> +     struct ahash_completion *res = req->data;
>> +
>> +     if (err == -EINPROGRESS)
>> +             return;
>> +     res->err = err;
>> +     complete(&res->completion);
>> +}
>> +
>> +static int ahash_wait(int err, struct ahash_completion *res)
>> +{
>> +     switch (err) {
>> +     case 0:
>> +             break;
>> +     case -EINPROGRESS:
>> +     case -EBUSY:
>> +             wait_for_completion(&res->completion);
>> +             reinit_completion(&res->completion);
>> +             err = res->err;
>> +             /* fall through */
>> +     default:
>> +             pr_crit("ahash calculation failed: err: %d\n", err);
>> +     }
>> +
>> +     return err;
>> +}
>> +
>> +static int ima_calc_file_hash_atfm(struct file *file,
>> +                                struct ima_digest_data *hash,
>> +                                struct crypto_ahash *tfm)
>> +{
>> +     loff_t i_size, offset;
>> +     char *rbuf;
>> +     int rc, read = 0, rbuf_len;
>> +     struct ahash_request *req;
>> +     struct scatterlist sg[1];
>> +     struct ahash_completion res;
>> +
>> +     hash->length = crypto_ahash_digestsize(tfm);
>> +
>> +     req = ahash_request_alloc(tfm, GFP_KERNEL);
>> +     if (!req)
>> +             return -ENOMEM;
>> +
>> +     init_completion(&res.completion);
>> +     ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG |
>> +                                CRYPTO_TFM_REQ_MAY_SLEEP,
>> +                                ahash_complete, &res);
>> +
>> +     rc = ahash_wait(crypto_ahash_init(req), &res);
>> +     if (rc)
>> +             goto out1;
>> +
>> +     i_size = i_size_read(file_inode(file));
>> +
>> +     if (i_size == 0)
>> +             goto out2;
>> +
>> +     rbuf = kzalloc(PAGE_SIZE, GFP_KERNEL);
>> +     if (!rbuf) {
>> +             rc = -ENOMEM;
>> +             goto out1;
>> +     }
>> +
>> +     if (!(file->f_mode & FMODE_READ)) {
>> +             file->f_mode |= FMODE_READ;
>> +             read = 1;
>> +     }
>> +
>> +     for (offset = 0; offset < i_size; offset += rbuf_len) {
>> +             rbuf_len = ima_kernel_read(file, offset, rbuf, PAGE_SIZE);
>> +             if (rbuf_len < 0) {
>> +                     rc = rbuf_len;
>> +                     vi break;
>> +             }
>> +             if (rbuf_len == 0)
>> +                     break;
>> +
>> +             sg_init_one(&sg[0], rbuf, rbuf_len);
>> +             ahash_request_set_crypt(req, sg, NULL, rbuf_len);
>> +
>> +             rc = ahash_wait(crypto_ahash_update(req), &res);
>> +             if (rc)
>> +                     break;
>> +     }
>> +     if (read)
>> +             file->f_mode &= ~FMODE_READ;
>> +     kfree(rbuf);
>> +out2:
>> +     if (!rc) {
>> +             ahash_request_set_crypt(req, NULL, hash->digest, 0);
>> +             rc = ahash_wait(crypto_ahash_final(req), &res);
>> +     }
>> +out1:
>> +     ahash_request_free(req);
>> +     return rc;
>> +}
>> +
>> +static int ima_calc_file_ahash(struct file *file, struct ima_digest_data *hash)
>> +{
>> +     struct crypto_ahash *tfm;
>> +     int rc;
>> +
>> +     tfm = ima_alloc_atfm(hash->algo);
>> +     if (IS_ERR(tfm))
>> +             return PTR_ERR(tfm);
>> +
>> +     rc = ima_calc_file_hash_atfm(file, hash, tfm);
>> +
>> +     ima_free_atfm(tfm);
>> +
>> +     return rc;
>> +}
>> +
>>  static int ima_calc_file_hash_tfm(struct file *file,
>>                                 struct ima_digest_data *hash,
>>                                 struct crypto_shash *tfm)
>> @@ -156,7 +313,7 @@ out:
>>       return rc;
>>  }
>>
>> -int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
>> +static int ima_calc_file_shash(struct file *file, struct ima_digest_data *hash)
>>  {
>>       struct crypto_shash *tfm;
>>       int rc;
>> @@ -172,6 +329,26 @@ int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
>>       return rc;
>>  }
>>
>> +int ima_calc_file_hash(struct file *file, struct ima_digest_data *hash)
>> +{
>> +     loff_t i_size;
>> +     int rc;
>> +
>> +     i_size = i_size_read(file_inode(file));
>
> Depending on the config options, i_size_read() does more than just
> access the inode's i_size.   Instead of calling it again, perhaps it
> should be passed to ima_calc_file_hash()/ahash().
>

I thought about it.. Indeed let's make it like that.


>> +
>> +     /* shash is more efficient for small data
>> +      * ahash performance depends on data size and particular HW
>> +      * ima_ahash_size allows to specify the best value for the system
>> +      */
>
> Function descriptions belong above the function, not inside.
>

This is a comment to the code..

>> +     if (ima_ahash_size && i_size >= ima_ahash_size) {
>> +             rc = ima_calc_file_ahash(file, hash);
>> +             if (!rc)
>> +                     return 0;
>> +     }
>> +     /* fallback to shash if ahash failed */
>
> Same here.
>

Same here...

But sure it can move to function description...

> thanks,
>
> Mimi
>
>> +     return ima_calc_file_shash(file, hash);
>> +}
>> +
>>  /*
>>   * Calculate the hash of template data
>>   */
>
>

Thanks.
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