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Message-ID: <aPYg1N0TvrkG6AJI@earth.li>
Date: Mon, 20 Oct 2025 12:45:24 +0100
From: Jonathan McDowell <noodles@...th.li>
To: Jarkko Sakkinen <jarkko@...nel.org>
Cc: linux-integrity@...r.kernel.org, keyring@...r.kernel.org,
dpsmith@...rtussolutions.com, ross.philipson@...cle.com,
Roberto Sassu <roberto.sassu@...wei.com>,
Stefano Garzarella <sgarzare@...hat.com>,
Jarkko Sakkinen <jarkko.sakkinen@...nsys.com>,
Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 01/10] tpm: Cap the number of PCR banks
On Sat, Oct 18, 2025 at 02:17:16PM +0300, Jarkko Sakkinen wrote:
>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 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@...a.com>
>Cc: Roberto Sassu <roberto.sassu@...wei.com>
>Fixes: bcfff8384f6c ("tpm: dynamically allocate the allocated_banks array")
>Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...nsys.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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