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Message-ID: <1404319243.596.55.camel@dhcp-9-2-203-236.watson.ibm.com>
Date: Wed, 02 Jul 2014 12:40:43 -0400
From: Mimi Zohar <zohar@...ux.vnet.ibm.com>
To: Dmitry Kasatkin <dmitry.kasatkin@...il.com>
Cc: linux-ima-devel@...ts.sourceforge.net,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
Dmitry Kasatkin <d.kasatkin@...sung.com>
Subject: Re: [PATCH v2 1/3] ima: use ahash API for file hash calculation
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 ...
> Signed-off-by: Dmitry Kasatkin <d.kasatkin@...sung.com>
> ---
> 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().
> +
> + /* 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.
> + 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.
thanks,
Mimi
> + return ima_calc_file_shash(file, hash);
> +}
> +
> /*
> * Calculate the hash of template data
> */
--
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