[PATCH 2/2] ima: support calculating the boot_aggregate based on different TPM banks

[Mimi Zohar]

Calculating the boot_aggregate attempts to read the TPM SHA1 bank,
assuming it is always enabled.  With TPM 2.0 hash agility, TPM chips
could support multiple TPM PCR banks, allowing firmware to configure and
enable different banks.

Instead of hard coding the TPM 2.0 bank hash algorithm used for calculating
the boot-aggregate, see if the configured IMA_DEFAULT_HASH algorithm is
an allocated TPM bank, otherwise use the first allocated TPM bank.

For TPM 1.2 SHA1 is the only supported hash algorithm.

Reported-by: Jerry Snitselaar <jsnitsel@xxxxxxxxxx>
Signed-off-by: Mimi Zohar <zohar@xxxxxxxxxxxxx>
---
 security/integrity/ima/ima_crypto.c | 37 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/security/integrity/ima/ima_crypto.c b/security/integrity/ima/ima_crypto.c
index 7967a6904851..b1b26d61f174 100644
--- a/security/integrity/ima/ima_crypto.c
+++ b/security/integrity/ima/ima_crypto.c
@@ -656,8 +656,25 @@ static void __init ima_pcrread(u32 idx, struct tpm_digest *d)
 		pr_err("Error Communicating to TPM chip\n");
 }
 
+/* tpm2_hash_map is the same as defined in tpm2-cmd.c and trusted_tpm2.c */
+static struct tpm2_hash tpm2_hash_map[] = {
+	{HASH_ALGO_SHA1, TPM_ALG_SHA1},
+	{HASH_ALGO_SHA256, TPM_ALG_SHA256},
+	{HASH_ALGO_SHA384, TPM_ALG_SHA384},
+	{HASH_ALGO_SHA512, TPM_ALG_SHA512},
+	{HASH_ALGO_SM3_256, TPM_ALG_SM3_256},
+};
+
 /*
- * Calculate the boot aggregate hash
+ * The boot_aggregate is a cumulative hash over TPM registers 0 - 7.  With
+ * TPM 2.0 hash agility, TPM chips could support multiple TPM PCR banks,
+ * allowing firmware to configure and enable different banks.
+ *
+ * Instead of hard coding the TPM bank hash algorithm used for calculating
+ * the boot-aggregate, see if the configured IMA_DEFAULT_HASH algorithm is
+ * an allocated TPM bank, otherwise use the first allocated TPM bank.
+ *
+ * For TPM 1.2 SHA1 is the only hash algorithm.
  */
 static int __init ima_calc_boot_aggregate_tfm(char *digest,
 					      struct crypto_shash *tfm)
@@ -673,6 +690,24 @@ static int __init ima_calc_boot_aggregate_tfm(char *digest,
 	if (rc != 0)
 		return rc;
 
+	for (i = 0; i < ARRAY_SIZE(tpm2_hash_map); i++) {
+		if (tpm2_hash_map[i].crypto_id == ima_hash_algo) {
+			d.alg_id = tpm2_hash_map[i].tpm_id;
+			break;
+		}
+	}
+
+	for (i = 0; i < ima_tpm_chip->nr_allocated_banks; i++) {
+		if (ima_tpm_chip->allocated_banks[i].alg_id == d.alg_id)
+			break;
+	}
+
+	if (i == ima_tpm_chip->nr_allocated_banks)
+		d.alg_id = ima_tpm_chip->allocated_banks[0].alg_id;
+
+	pr_info("Calculating the boot-aggregregate, reading TPM PCR bank: %04x",
+		d.alg_id);
+
 	/* cumulative sha1 over tpm registers 0-7 */
 	for (i = TPM_PCR0; i < TPM_PCR8; i++) {
 		ima_pcrread(i, &d);
-- 
2.7.5