linux-kernel - [PATCH v8 01/11] tpm: Cap the number of PCR banks

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Message-ID: <20251127214138.3760029-2-jarkko@kernel.org>
Date: Thu, 27 Nov 2025 23:41:26 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: linux-integrity@...r.kernel.org
Cc: ross.philipson@...cle.com,
	Jonathan McDowell <noodles@...th.li>,
	Stefano Garzarella <sgarzare@...hat.com>,
	Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
	Roberto Sassu <roberto.sassu@...wei.com>,
	stable@...r.kernel.org,
	Jonathan McDowell <noodles@...a.com>,
	Peter Huewe <peterhuewe@....de>,
	Jarkko Sakkinen <jarkko@...nel.org>,
	Jason Gunthorpe <jgg@...pe.ca>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v8 01/11] tpm: Cap the number of PCR banks

From: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>

tpm2_get_pcr_allocation() does not cap any upper limit for the number of
banks. Cap the limit to eight banks so that out of bounds values coming
from external I/O cause on only limited harm.

Cc: Roberto Sassu <roberto.sassu@...wei.com>
Cc: stable@...r.kernel.org # v5.10+
Fixes: bcfff8384f6c ("tpm: dynamically allocate the allocated_banks array")
Reviewed-by: Jonathan McDowell <noodles@...a.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>
---
v8:
- Remove unrelated change of removing tpm1_get_pcr_allocation.
- Add the missing '\n' to the error message.
v7:
- In Ryzen desktop there is total three banks so yep, eight is probably
  much safer bet than four banks. Fixed the commit message as per remark
  from Jonathan:

  https://lore.kernel.org/linux-integrity/aPYg1N0TvrkG6AJI@earth.li/#t

  And with that added also reviewed-by.
v6
- No changes.
v5:
- No changes.
v4:
- Revert spurious changes from include/linux/tpm.h.
- Increase TPM2_MAX_BANKS to 8.
- Rename TPM2_MAX_BANKS as TPM2_MAX_PCR_BANKS for the sake of clarity.
v3:
- Wrote a more clear commit message.
- Fixed pr_err() message.
v2:
- A new patch.
---
 drivers/char/tpm/tpm1-cmd.c | 5 -----
 drivers/char/tpm/tpm2-cmd.c | 8 +++-----
 include/linux/tpm.h         | 8 +++++---
 3 files changed, 8 insertions(+), 13 deletions(-)

diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
index 11088bda4e68..6849f216ba0b 100644
--- a/drivers/char/tpm/tpm1-cmd.c
+++ b/drivers/char/tpm/tpm1-cmd.c
@@ -799,11 +799,6 @@ int tpm1_pm_suspend(struct tpm_chip *chip, u32 tpm_suspend_pcr)
  */
 int tpm1_get_pcr_allocation(struct tpm_chip *chip)
 {
-	chip->allocated_banks = kcalloc(1, sizeof(*chip->allocated_banks),
-					GFP_KERNEL);
-	if (!chip->allocated_banks)
-		return -ENOMEM;
-
 	chip->allocated_banks[0].alg_id = TPM_ALG_SHA1;
 	chip->allocated_banks[0].digest_size = hash_digest_size[HASH_ALGO_SHA1];
 	chip->allocated_banks[0].crypto_id = HASH_ALGO_SHA1;
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 7d77f6fbc152..5b6ccf901623 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -538,11 +538,9 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
 
 	nr_possible_banks = be32_to_cpup(
 		(__be32 *)&buf.data[TPM_HEADER_SIZE + 5]);
-
-	chip->allocated_banks = kcalloc(nr_possible_banks,
-					sizeof(*chip->allocated_banks),
-					GFP_KERNEL);
-	if (!chip->allocated_banks) {
+	if (nr_possible_banks > TPM2_MAX_PCR_BANKS) {
+		pr_err("tpm: out of bank capacity: %u > %u\n",
+		       nr_possible_banks, TPM2_MAX_PCR_BANKS);
 		rc = -ENOMEM;
 		goto out;
 	}
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index dc0338a783f3..eb0ff071bcae 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -26,7 +26,9 @@
 #include <crypto/aes.h>
 
 #define TPM_DIGEST_SIZE 20	/* Max TPM v1.2 PCR size */
-#define TPM_MAX_DIGEST_SIZE SHA512_DIGEST_SIZE
+
+#define TPM2_MAX_DIGEST_SIZE	SHA512_DIGEST_SIZE
+#define TPM2_MAX_PCR_BANKS	8
 
 struct tpm_chip;
 struct trusted_key_payload;
@@ -68,7 +70,7 @@ enum tpm2_curves {
 
 struct tpm_digest {
 	u16 alg_id;
-	u8 digest[TPM_MAX_DIGEST_SIZE];
+	u8 digest[TPM2_MAX_DIGEST_SIZE];
 } __packed;
 
 struct tpm_bank_info {
@@ -189,7 +191,7 @@ struct tpm_chip {
 	unsigned int groups_cnt;
 
 	u32 nr_allocated_banks;
-	struct tpm_bank_info *allocated_banks;
+	struct tpm_bank_info allocated_banks[TPM2_MAX_PCR_BANKS];
 #ifdef CONFIG_ACPI
 	acpi_handle acpi_dev_handle;
 	char ppi_version[TPM_PPI_VERSION_LEN + 1];
-- 
2.52.0