[PATCH 8/8] ima: switch to ima_hash_algo for boot aggregate

Roberto Sassu
2020-01-27T17:07:27Z

boot_aggregate is the first entry of IMA measurement list. Its purpose is
to link pre-boot measurements to IMA measurements. As IMA was designed to
work with a TPM 1.2, the SHA1 PCR bank was always selected.

Currently, even if a TPM 2.0 is used, the SHA1 PCR bank is selected.
However, the assumption that the SHA1 PCR bank is always available is not
correct, as PCR banks can be selected with the PCR_Allocate() TPM command.

This patch tries to use ima_hash_algo as hash algorithm for boot_aggregate.
If no PCR bank uses that algorithm, the patch scans the allocated PCR banks
and selects the first for which the mapping between TPM algorithm ID and
crypto algorithm ID is known. If no suitable algorithm is found, an error
is returned.

Signed-off-by: Roberto Sassu <roberto.sassu@huawei.com>
---
security/integrity/ima/ima_crypto.c | 38 +++++++++++++++++------------
security/integrity/ima/ima_init.c | 6 ++---
2 files changed, 25 insertions(+), 19 deletions(-)

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index f84dfd8fc5ca..9bf5e69945b7 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -780,25 +780,27 @@ static void __init ima_pcrread(u32 idx, struct tpm_digest *d)
/*
* Calculate the boot aggregate hash
*/
-static int __init ima_calc_boot_aggregate_tfm(char *digest,
- struct crypto_shash *tfm)
+static int __init ima_calc_boot_aggregate_tfm(char *digest, int bank_idx)
{
- struct tpm_digest d = { .alg_id = TPM_ALG_SHA1, .digest = {0} };
+ struct tpm_digest d = { .digest = {0} };
int rc;
u32 i;
- SHASH_DESC_ON_STACK(shash, tfm);
+ SHASH_DESC_ON_STACK(shash, ima_algo_array[bank_idx].tfm);

- shash->tfm = tfm;
+ shash->tfm = ima_algo_array[bank_idx].tfm;

rc = crypto_shash_init(shash);
if (rc != 0)
return rc;

+ d.alg_id = ima_tpm_chip->allocated_banks[bank_idx].alg_id;
+
/* cumulative sha1 over tpm registers 0-7 */
for (i = TPM_PCR0; i < TPM_PCR8; i++) {
ima_pcrread(i, &d);
/* now accumulate with current aggregate */
- rc = crypto_shash_update(shash, d.digest, TPM_DIGEST_SIZE);
+ rc = crypto_shash_update(shash, d.digest,
+ ima_tpm_chip->allocated_banks[bank_idx].digest_size);
}
if (!rc)
crypto_shash_final(shash, digest);
@@ -807,17 +809,21 @@ static int __init ima_calc_boot_aggregate_tfm(char *digest,

int __init ima_calc_boot_aggregate(struct ima_digest_data *hash)
{
- struct crypto_shash *tfm;
- int rc;
+ int bank_idx = ima_hash_algo_idx;

- tfm = ima_alloc_tfm(hash->algo);
- if (IS_ERR(tfm))
- return PTR_ERR(tfm);
-
- hash->length = crypto_shash_digestsize(tfm);
- rc = ima_calc_boot_aggregate_tfm(hash->digest, tfm);
+ if (bank_idx >= ima_tpm_chip->nr_allocated_banks) {
+ for (bank_idx = 0; bank_idx < ima_tpm_chip->nr_allocated_banks;
+ bank_idx++)
+ if (ima_algo_array[bank_idx].tfm)
+ break;

- ima_free_tfm(tfm);
+ if (bank_idx == ima_tpm_chip->nr_allocated_banks) {
+ pr_err("No suitable algo found for boot aggregate\n");
+ return -ENOENT;
+ }
+ }

- return rc;
+ hash->algo = ima_algo_array[bank_idx].algo;
+ hash->length = crypto_shash_digestsize(ima_algo_array[bank_idx].tfm);
+ return ima_calc_boot_aggregate_tfm(hash->digest, bank_idx);
}
diff --git a/security/integrity/ima/ima_init.c b/security/integrity/ima/ima_init.c
index 195cb4079b2b..b4da190a33ba 100644
--- a/security/integrity/ima/ima_init.c
+++ b/security/integrity/ima/ima_init.c
@@ -51,14 +51,14 @@ static int __init ima_add_boot_aggregate(void)
int violation = 0;
struct {
struct ima_digest_data hdr;
- char digest[TPM_DIGEST_SIZE];
+ char digest[SHA512_DIGEST_SIZE];
} hash;

memset(iint, 0, sizeof(*iint));
memset(&hash, 0, sizeof(hash));
iint->ima_hash = &hash.hdr;
- iint->ima_hash->algo = HASH_ALGO_SHA1;
- iint->ima_hash->length = SHA1_DIGEST_SIZE;
+ iint->ima_hash->algo = ima_hash_algo;
+ iint->ima_hash->length = hash_digest_size[ima_hash_algo];

if (ima_tpm_chip) {
result = ima_calc_boot_aggregate(&hash.hdr);
--
2.17.1