[TrouSerS-users] ERROR Tspi_TPM_PcrReset: Bad input size

[Ismaël FEZZAZ]

Hi,

I am trying to use the Tspi_TPM_PcrReset(hTPM, hPcrs) function.
It is working for pcrs 16 and 23 and I can't reset pcrs 17 to 22 for
locality reason which is fine.
But when I try to reset pcrs from 0 to 15 I get an error Bad input size.
Any idea why it is happening ? and how to reset those pcrs ?

I am working on an arm embeded system with an i2c wired tpm chip:
Linux v2r1 3.14.36ltsi-yocto-standard #12 Tue Sep 15 11:57:15 CEST
2015 armv7l GNU/Linux

TPM 1.2 Version Info:
Chip Version: 1.2.66.4
Spec Level: 2
Errata Revision: 3
TPM Vendor ID: ATML
TPM Version: 01010000
Manufacturer Info: 41544d4c

Here is the code I used:

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

#include <trousers/tss.h>
#include <trousers/trousers.h>

static void exit_on_error(char *msg, int status)
{
fprintf(stderr, "%s\n", msg);
exit(status);
}

static void check_args(int argc, char *argv[], UINT32 *pcrIndex)
{
if (argc != 2 || strcmp(argv[1], "-h") == 0 || strcmp(argv[1], "--help") == 0)
exit_on_error("Usage: reset_pcr pcrIndex\n", 1);

*pcrIndex = strtol(argv[1], NULL, 0);
if (errno == ERANGE || errno == EINVAL || *pcrIndex > 23)
exit_on_error("pcrIndex must be an int between 0 and 23\n", 1);
}

int main(int argc, char *argv[])
{
TSS_HCONTEXT hContext = 0;
TSS_HTPM hTPM = 0;
TSS_RESULT result;
TSS_HPCRS hPcrs;
UINT32 pcrIndex = 0;

check_args(argc, argv, &pcrIndex);

if ((result = Tspi_Context_Create(&hContext)) != TSS_SUCCESS)
exit_on_error(Trspi_Error_String(result), 2);
if ((result = Tspi_Context_Connect(hContext, NULL)) != TSS_SUCCESS)
exit_on_error(Trspi_Error_String(result), 3);
if ((result = Tspi_Context_GetTpmObject(hContext, &hTPM)) != TSS_SUCCESS)
exit_on_error(Trspi_Error_String(result), 4);

if ((result = Tspi_Context_CreateObject(hContext, TSS_OBJECT_TYPE_PCRS,
0, &hPcrs)) != TSS_SUCCESS)
exit_on_error(Trspi_Error_String(result), 5);

if ((result = Tspi_PcrComposite_SelectPcrIndex(hPcrs,
pcrIndex)) != TSS_SUCCESS)
exit_on_error(Trspi_Error_String(result), 6);

if ((result = Tspi_TPM_PcrReset(hTPM, hPcrs)) != TSS_SUCCESS)
exit_on_error(Trspi_Error_String(result), 7);


Tspi_Context_FreeMemory(hContext, NULL);
Tspi_Context_Close(hContext);
return 0;
}

Thanks.

[Ken Goldman]

Post by Ismaël FEZZAZ
Hi,
I am trying to use the Tspi_TPM_PcrReset(hTPM, hPcrs) function.
It is working for pcrs 16 and 23 and I can't reset pcrs 17 to 22 for
locality reason which is fine.
But when I try to reset pcrs from 0 to 15 I get an error Bad input size.
Any idea why it is happening ? and how to reset those pcrs ?

You should get a copy of the published PC Client TPM spec. It will
answer this question and probably a lot more.

For security reasons, the only way to reset PCR 0-15 is to reboot.

If you want to know the rationale, read part 1 of the TPM main spec,
which discusses the TPM architecture.



------------------------------------------------------------------------------