Re: [PATCH v1 1/3] ima: use ahash API for file hash calculation

[Mimi Zohar]

On Thu, 2014-06-19 at 18:20 +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 peformance depends on data size and particular HW. Under certain
> limit, depending on the system, shash performance may be better.
> 
> This patch also introduces 'ima_ahash_size' kernel parameter which can
> be used to defines minimal data size to use with ahash. When this
> parameter is not set or file size is smaller than defined by this
> parameter, shash will be used. Thus, by defult, original shash
> implementation is used.
> 
> Signed-off-by: Dmitry Kasatkin <d.kasatkin@xxxxxxxxxxx>
> ---
>  Documentation/kernel-parameters.txt |   3 +
>  security/integrity/ima/ima_crypto.c | 182 +++++++++++++++++++++++++++++++++++-
>  2 files changed, 181 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index a0c155c..f8efb01 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -1286,6 +1286,9 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
>  	ihash_entries=	[KNL]
>  			Set number of hash buckets for inode cache.
> 
> +	ima_ahash_size=size [IMA]
> +			Set the minimal file size when use ahash API.
> +
>  	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 ccd0ac8..b7a8650 100644
> --- a/security/integrity/ima/ima_crypto.c
> +++ b/security/integrity/ima/ima_crypto.c
> @@ -25,7 +25,25 @@
>  #include <crypto/hash_info.h>
>  #include "ima.h"
> 
> +
> +struct ahash_completion {
> +	struct completion completion;
> +	int err;
> +};
> +
>  static struct crypto_shash *ima_shash_tfm;
> +static struct crypto_ahash *ima_ahash_tfm;
> +
> +/* data size for ahash use */
> +static loff_t ima_ahash_size;
> +
> +static int __init ima_ahash_setup(char *str)
> +{
> +	int rc = kstrtoll(str, 10, &ima_ahash_size);

In general, variable definitions should be separated from code.  A
simple initialization is fine.  Please separate variable definitions
from code with a blank line. 

> +	pr_info("ima_ahash_size = %lld\n", ima_ahash_size);
> +	return !rc;
> +}
> +__setup("ima_ahash_size=", ima_ahash_setup);

This boot parameter name doesn't reflect its purpose, defining the
minimum file size for using ahash. The next patch defines an additional
boot parameter ima_ahash_bufsize. Perhaps defining a single boot
parameter (eg. ima_ahash=) with multiple fields would be better. 

>  /**
>   * ima_kernel_read - read file content
> @@ -68,6 +86,14 @@ int ima_init_crypto(void)
>  		       hash_algo_name[ima_hash_algo], rc);
>  		return rc;
>  	}
> +	ima_ahash_tfm = crypto_alloc_ahash(hash_algo_name[ima_hash_algo], 0, 0);
> +	if (IS_ERR(ima_ahash_tfm)) {
> +		rc = PTR_ERR(ima_ahash_tfm);
> +		crypto_free_shash(ima_shash_tfm);

Only crypto_alloc_ahash() failed, not crypto_alloc_shash(). shash has
worked fine up to now. Why require both shash and ahash to succeed? 

> +		pr_err("Can not allocate %s (reason: %ld)\n",
> +		       hash_algo_name[ima_hash_algo], rc);
> +		return rc;
> +	}
>  	return 0;
>  }
> 

> @@ -93,9 +119,143 @@ 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 = crypto_alloc_ahash(hash_algo_name[algo], 0, 0);
> +		if (IS_ERR(tfm)) {
> +			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(ima_ahash_tfm, GFP_KERNEL);

This should be tfm not ima_ahash_tfm.

> +	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;
> +			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 +316,7 @@ 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 +332,20 @@ 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 = i_size_read(file_inode(file));
> +
> +	/* shash is more efficient small data
> +	 * ahash performance depends on data size and particular HW
> +	 * ima_ahash_size allows to specify the best value for the system
> +	 */
> +	if (ima_ahash_size && i_size >= ima_ahash_size)
> +		return ima_calc_file_ahash(file, hash);
> +	else
> +		return ima_calc_file_shash(file, hash);
> +}

If calculating the file hash using ahash fails, should it fall back to
using shash?

Mimi

>  /*
>   * Calculate the hash of template data
>   */



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