[PATCH v7 01/11] tpm: Cap the number of PCR banks

Jarkko Sakkinen
2025-11-27T13:54:57Z

From: Jarkko Sakkinen <jarkko.sakkinen@opinsys.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@huawei.com>
Fixes: bcfff8384f6c ("tpm: dynamically allocate the allocated_banks array")
Reviewed-By: Jonathan McDowell <noodles@meta.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@opinsys.com>
---
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/tpm-chip.c | 13 +++++++++----
drivers/char/tpm/tpm.h | 1 -
drivers/char/tpm/tpm1-cmd.c | 25 -------------------------
drivers/char/tpm/tpm2-cmd.c | 8 +++-----
include/linux/tpm.h | 8 +++++---
5 files changed, 17 insertions(+), 38 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index e25daf2396d3..6cb25862688f 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -559,14 +559,19 @@ static int tpm_add_hwrng(struct tpm_chip *chip)

static int tpm_get_pcr_allocation(struct tpm_chip *chip)
{
- int rc;
+ int rc = 0;

if (tpm_is_firmware_upgrade(chip))
return 0;

- rc = (chip->flags & TPM_CHIP_FLAG_TPM2) ?
- tpm2_get_pcr_allocation(chip) :
- tpm1_get_pcr_allocation(chip);
+ if (!(chip->flags & TPM_CHIP_FLAG_TPM2)) {
+ 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;
+ chip->nr_allocated_banks = 1;
+ } else {
+ rc = tpm2_get_pcr_allocation(chip);
+ }

if (rc > 0)
return -ENODEV;
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 2726bd38e5ac..a37712c02e44 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -252,7 +252,6 @@ int tpm1_pcr_read(struct tpm_chip *chip, u32 pcr_idx, u8 *res_buf);
ssize_t tpm1_getcap(struct tpm_chip *chip, u32 subcap_id, cap_t *cap,
const char *desc, size_t min_cap_length);
int tpm1_get_random(struct tpm_chip *chip, u8 *out, size_t max);
-int tpm1_get_pcr_allocation(struct tpm_chip *chip);
unsigned long tpm_calc_ordinal_duration(struct tpm_chip *chip, u32 ordinal);
int tpm_pm_suspend(struct device *dev);
int tpm_pm_resume(struct device *dev);
diff --git a/drivers/char/tpm/tpm1-cmd.c b/drivers/char/tpm/tpm1-cmd.c
index 11088bda4e68..708bc553437b 100644
--- a/drivers/char/tpm/tpm1-cmd.c
+++ b/drivers/char/tpm/tpm1-cmd.c
@@ -786,28 +786,3 @@ int tpm1_pm_suspend(struct tpm_chip *chip, u32 tpm_suspend_pcr)

return rc;
}
-
-/**
- * tpm1_get_pcr_allocation() - initialize the allocated bank
- * @chip: TPM chip to use.
- *
- * The function initializes the SHA1 allocated bank to extend PCR
- *
- * Return:
- * * 0 on success,
- * * < 0 on error.
- */
-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;
- chip->nr_allocated_banks = 1;
-
- return 0;
-}
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index 7d77f6fbc152..97501c567c34 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: unexpected number of banks: %u > %u",
+ 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