Re: [PATCH v7 1/5] tpm: dynamically allocate the allocated_banks array

From: Roberto Sassu
Date: Mon Jan 07 2019 - 05:06:49 EST

On 12/22/2018 1:03 AM, Jarkko Sakkinen wrote:
On Fri, Dec 21, 2018 at 10:40:09AM +0100, Roberto Sassu wrote:
On 12/20/2018 3:55 PM, Jarkko Sakkinen wrote:
On Thu, Dec 13, 2018 at 11:29:41AM +0100, Roberto Sassu wrote:
This patch renames active_banks (member of tpm_chip) to allocated_banks,
stores the number of allocated PCR banks in nr_allocated_banks (new member
of tpm_chip), and replaces the static array with a pointer to a dynamically
allocated array.

tpm2_get_pcr_allocation() determines if a PCR bank is allocated by checking
the mask in the TPML_PCR_SELECTION structure returned by the TPM for
TPM2_Get_Capability(). If a bank is not allocated, the TPM returns that
bank in TPML_PCR_SELECTION, with all bits in the mask set to zero. In this
case, the bank is not included in chip->allocated_banks, to avoid that TPM
driver users unnecessarily calculate a digest for that bank.

One PCR bank with algorithm set to SHA1 is always allocated for TPM 1.x.

As a consequence of the introduction of nr_allocated_banks,
tpm_pcr_extend() does not check anymore if the algorithm stored in tpm_chip
is equal to zero.

Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@xxxxxxxxxxxxxxx>
drivers/char/tpm/tpm-chip.c | 1 +
drivers/char/tpm/tpm-interface.c | 18 +++++++++--------
drivers/char/tpm/tpm.h | 3 ++-
drivers/char/tpm/tpm1-cmd.c | 10 ++++++++++
drivers/char/tpm/tpm2-cmd.c | 34 ++++++++++++++++++++++----------
5 files changed, 47 insertions(+), 19 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 32db84683c40..ce851c62bb68 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -160,6 +160,7 @@ static void tpm_dev_release(struct device *dev)
+ kfree(chip->allocated_banks);
diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index d9439f9abe78..7b80919228be 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -488,8 +488,7 @@ EXPORT_SYMBOL_GPL(tpm_pcr_read);
int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash)
int rc;
- struct tpm2_digest digest_list[ARRAY_SIZE(chip->active_banks)];
- u32 count = 0;
+ struct tpm2_digest *digest_list;
int i;
chip = tpm_find_get_ops(chip);
@@ -497,16 +496,19 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx, const u8 *hash)
return -ENODEV;
if (chip->flags & TPM_CHIP_FLAG_TPM2) {
- memset(digest_list, 0, sizeof(digest_list));
+ digest_list = kcalloc(chip->nr_allocated_banks,
+ sizeof(*digest_list), GFP_KERNEL);
+ if (!digest_list)
+ return -ENOMEM;

You could preallocate digest list and place it to struct tpm_chip
instead of doing it everytime tpm_pcr_extend() called.

This part will be removed with patch 5/5.

Even if it did, it does not make this patch unbroken.

Can two calls to tpm_pcr_extend() be executed at the same time?

If yes, the digest list should be protected by a mutex.



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