[RFC PATCH v1 5/7] tpm: enable bank selection for PCR extend

Nicolai Stange
2025-03-13T17:35:17Z

The existing tpm_pcr_extend() extends all of a PCR's allocated banks with
the corresponding digest from the provided digests[] argument.

An upcoming code change to IMA will introduce the need to skip over those
banks it does not have a hash algorithm implementation available for.

Introduce tpm_pcr_extend_sel() to support this.

tpm_pcr_extend_sel() also expects a digests[] array, always being the
number of allocated PCR banks in size, just as it's the case for the
existing tpm_pcr_extend(). In addition to that however, it takes a
'banks_skip_mask', and will skip the extension of any bank having its
corresponding bit set there.

Signed-off-by: Nicolai Stange <nstange@suse.de>
---
drivers/char/tpm/tpm-interface.c | 29 +++++++++++++++++++++++++++--
drivers/char/tpm/tpm.h | 3 ++-
drivers/char/tpm/tpm2-cmd.c | 29 +++++++++++++++++++++++++++--
include/linux/tpm.h | 3 +++
4 files changed, 59 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm-interface.c b/drivers/char/tpm/tpm-interface.c
index b1daa0d7b341..2bab251034b5 100644
--- a/drivers/char/tpm/tpm-interface.c
+++ b/drivers/char/tpm/tpm-interface.c
@@ -314,6 +314,26 @@ EXPORT_SYMBOL_GPL(tpm_pcr_read);
*/
int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
struct tpm_digest *digests)
+{
+ return tpm_pcr_extend_sel(chip, pcr_idx, digests, 0);
+}
+EXPORT_SYMBOL_GPL(tpm_pcr_extend);
+
+/**
+ * tpm_pcr_extend_sel - extend a PCR value into selected banks.
+ * @chip: a &struct tpm_chip instance, %NULL for the default chip
+ * @pcr_idx: the PCR to be retrieved
+ * @digests: array of tpm_digest structures used to extend PCRs
+ * @banks_skip_mask: pcr banks to skip
+ *
+ * Note: callers must pass a digest for every allocated PCR bank, in the same
+ * order of the banks in chip->allocated_banks.
+ *
+ * Return: same as with tpm_transmit_cmd()
+ */
+int tpm_pcr_extend_sel(struct tpm_chip *chip, u32 pcr_idx,
+ struct tpm_digest *digests,
+ unsigned long banks_skip_mask)
{
int rc;
int i;
@@ -330,7 +350,13 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
}

if (chip->flags & TPM_CHIP_FLAG_TPM2) {
- rc = tpm2_pcr_extend(chip, pcr_idx, digests);
+ rc = tpm2_pcr_extend(chip, pcr_idx, digests, 0);
+ goto out;
+ }
+
+ /* There's only one SHA1 bank with TPM 1. */
+ if (banks_skip_mask & 1) {
+ rc = 0;
goto out;
}

@@ -341,7 +367,6 @@ int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
tpm_put_ops(chip);
return rc;
}
-EXPORT_SYMBOL_GPL(tpm_pcr_extend);

int tpm_auto_startup(struct tpm_chip *chip)
{
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index 7bb87fa5f7a1..f4ed49cb4101 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -291,7 +291,8 @@ int tpm2_get_timeouts(struct tpm_chip *chip);
int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
struct tpm_digest *digest, u16 *digest_size_ptr);
int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
- struct tpm_digest *digests);
+ struct tpm_digest *digests,
+ unsigned long banks_skip_mask);
int tpm2_get_random(struct tpm_chip *chip, u8 *dest, size_t max);
ssize_t tpm2_get_tpm_pt(struct tpm_chip *chip, u32 property_id,
u32 *value, const char *desc);
diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
index dfdcbd009720..23ded8ea47dc 100644
--- a/drivers/char/tpm/tpm2-cmd.c
+++ b/drivers/char/tpm/tpm2-cmd.c
@@ -226,16 +226,34 @@ int tpm2_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
* @chip: TPM chip to use.
* @pcr_idx: index of the PCR.
* @digests: list of pcr banks and corresponding digest values to extend.
+ * @banks_skip_mask: pcr banks to skip
*
* Return: Same as with tpm_transmit_cmd.
*/
int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
- struct tpm_digest *digests)
+ struct tpm_digest *digests,
+ unsigned long banks_skip_mask)
{
struct tpm_buf buf;
+ unsigned long skip_mask;
+ u32 banks_count;
int rc;
int i;

+ banks_count = 0;
+ skip_mask = banks_skip_mask;
+ for (i = 0; i < chip->nr_allocated_banks; i++) {
+ const bool skip_bank = skip_mask & 1;
+
+ skip_mask >>= 1;
+ if (skip_bank)
+ continue;
+ banks_count++;
+ }
+
+ if (banks_count == 0)
+ return 0;
+
if (!disable_pcr_integrity) {
rc = tpm2_start_auth_session(chip);
if (rc)
@@ -257,9 +275,16 @@ int tpm2_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
tpm_buf_append_auth(chip, &buf, 0, NULL, 0);
}

- tpm_buf_append_u32(&buf, chip->nr_allocated_banks);
+ tpm_buf_append_u32(&buf, banks_count);

+ skip_mask = banks_skip_mask;
for (i = 0; i < chip->nr_allocated_banks; i++) {
+ const bool skip_bank = skip_mask & 1;
+
+ skip_mask >>= 1;
+ if (skip_bank)
+ continue;
+
tpm_buf_append_u16(&buf, digests[i].alg_id);
tpm_buf_append(&buf, (const unsigned char *)&digests[i].digest,
chip->allocated_banks[i].digest_size);
diff --git a/include/linux/tpm.h b/include/linux/tpm.h
index 20a40ade8030..7587eecc82fd 100644
--- a/include/linux/tpm.h
+++ b/include/linux/tpm.h
@@ -447,6 +447,9 @@ extern int tpm_pcr_read(struct tpm_chip *chip, u32 pcr_idx,
struct tpm_digest *digest);
extern int tpm_pcr_extend(struct tpm_chip *chip, u32 pcr_idx,
struct tpm_digest *digests);
+extern int tpm_pcr_extend_sel(struct tpm_chip *chip, u32 pcr_idx,
+ struct tpm_digest *digests,
+ unsigned long banks_skip_mask);
extern int tpm_get_random(struct tpm_chip *chip, u8 *data, size_t max);
extern struct tpm_chip *tpm_default_chip(void);
void tpm2_flush_context(struct tpm_chip *chip, u32 handle);
--
2.47.1