Re: [PATCH v6 01/10] tpm: Cap the number of PCR banks

[Jonathan McDowell <noodles@earth.li>]

On Sat, Oct 18, 2025 at 02:17:16PM +0300, Jarkko Sakkinen wrote:
>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 four banks so that out of bounds values coming
>from external I/O cause on only limited harm.

Comment no longer matches code - we cap at 8. With the comment fixed:

Reviewed-By: Jonathan McDowell <noodles@meta.com>

>Cc: Roberto Sassu <roberto.sassu@huawei.com>
>Fixes: bcfff8384f6c ("tpm: dynamically allocate the allocated_banks array")
>Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@opinsys.com>
>---
>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 cf64c7385105..5c49bdff33de 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];
>-- 
>2.39.5

J.

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