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Date: Mon, 30 Jun 2014 17:58:04 +0300
From: Dmitry Kasatkin <d.kasatkin@...sung.com>
To: Mimi Zohar <zohar@...ux.vnet.ibm.com>
Cc: linux-ima-devel@...ts.sourceforge.net,
linux-security-module@...r.kernel.org,
linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
dmitry.kasatkin@...il.com
Subject: Re: [PATCH v1 1/3] ima: use ahash API for file hash calculation
On 26/06/14 14:54, Mimi Zohar wrote:
> 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@...sung.com>
>> ---
>> 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?
If ahash fails, then it could be a HW error, which should not happen.
IF HW fails device is broken.
Do you really want to fallback to shash?
Thanks,
Dmitry
> Mimi
>
>> /*
>> * Calculate the hash of template data
>> */
>
>
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