[PATCH] TPM: Fixup pcrs sysfs file

From: Jason Gunthorpe
Date: Tue Sep 01 2009 - 23:08:55 EST

I'm testing the tpm_tis low level driver with a winbond WPCT200:
$ cat caps
Manufacturer: 0x57454300
TCG version: 1.2
Firmware version: 2.16

and noted that tpm_pcr_read for the pcrs sysfile file does not function.
tpm_tis_recv returned with an error because the expected reply size was
set to 14 (the request size) and the chip returned 30 bytes.

The TCG spec says the reply size for READ_PCR is supposed to be 30 bytes.

The length input to transmit_cmd is the size of the reply, not of the

With this change my chip reports all 23 pcrs.

Also fix tpm_pcr_extend to match the idiom of the rest of the code to
prevent future confusion.

Finally, the BUILD_BUG_ON() is just wrong - it's testing a value which
isn't a compile-time constant. Simply remove that assertion, the
buffer is large enough by design.

Signed-off-by: Jason Gunthorpe <jgunthorpe@xxxxxxxxxxxxxxxxxxxx>
drivers/char/tpm/tpm.c | 8 +++-----
1 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index a6b52d6..5d5b324 100644
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -696,8 +696,7 @@ int __tpm_pcr_read(struct tpm_chip *chip, int pcr_idx, u8 *res_buf)

cmd.header.in = pcrread_header;
cmd.params.pcrread_in.pcr_idx = cpu_to_be32(pcr_idx);
- BUILD_BUG_ON(cmd.header.in.length > READ_PCR_RESULT_SIZE);
- rc = transmit_cmd(chip, &cmd, cmd.header.in.length,
+ rc = transmit_cmd(chip, &cmd, READ_PCR_RESULT_SIZE,
"attempting to read a pcr value");

if (rc == 0)
@@ -742,7 +741,7 @@ EXPORT_SYMBOL_GPL(tpm_pcr_read);
* the module usage count.
#define TPM_ORD_PCR_EXTEND cpu_to_be32(20)
-#define EXTEND_PCR_SIZE 34
static struct tpm_input_header pcrextend_header = {
.length = cpu_to_be32(34),
@@ -760,10 +759,9 @@ int tpm_pcr_extend(u32 chip_num, int pcr_idx, const u8 *hash)
return -ENODEV;

cmd.header.in = pcrextend_header;
- BUILD_BUG_ON(be32_to_cpu(cmd.header.in.length) > EXTEND_PCR_SIZE);
cmd.params.pcrextend_in.pcr_idx = cpu_to_be32(pcr_idx);
memcpy(cmd.params.pcrextend_in.hash, hash, TPM_DIGEST_SIZE);
- rc = transmit_cmd(chip, &cmd, cmd.header.in.length,
+ rc = transmit_cmd(chip, &cmd, EXTEND_PCR_RESULT_SIZE,
"attempting extend a PCR value");


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