[PATCH v2 3/3] tpm: Address !chip->auth in tpm_buf_append_hmac_session*()

[Jarkko Sakkinen]

On Thu Jul 4, 2024 at 4:56 AM EEST, Stefan Berger wrote:
>
>
> On 7/3/24 14:24, Jarkko Sakkinen wrote:
> > Unless tpm_chip_bootstrap() was called by the driver, !chip->auth can
>
> Doesn't tpm_chip_register() need to be called by all drivers? This 
> function then calls tpm_chip_bootstrap().
>
> > cause a null derefence in tpm_buf_hmac_session*().  Thus, address
> > !chip->auth in tpm_buf_hmac_session*() and remove the fallback
> > implementation for !TCG_TPM2_HMAC.
> > 
> > Cc: stable at vger.kernel.org # v6.9+
> > Reported-by: Stefan Berger <stefanb at linux.ibm.com>
> > Closes: https://lore.kernel.org/linux-integrity/20240617193408.1234365-1-stefanb@linux.ibm.com/
> > Fixes: 1085b8276bb4 ("tpm: Add the rest of the session HMAC API")
> > Signed-off-by: Jarkko Sakkinen <jarkko at kernel.org>
>
> I applied this series now but it doesn't solve the reported problem. The 

It fixes the issues of which symptoms was shown by your transcript:

[    2.987131] tpm tpm0: tpm2_load_context: failed with a TPM error 0x01C4
[    2.987140] ima: Error Communicating to TPM chip, result: -14

Your original thread identified zero problems, so thus your claim here
is plain untrue.

Before the null derefence is fixed all other patches related are
blocked, including ibm_tpmvtpm patches, because it would be insane
to accept them when there is known memory corruption bug, which
this patch set fixes.

What is so difficult to understand in this?

> error message is gone but the feature can still be enabled 
> (CONFIG_TCG_TPM2_HMAC=y) but is unlikely actually doing what it is 
> promising to do with this config option. So you either still have to 
> apply my patch, James's patch, or your intended "depends on 
> !TCG_IBMVTPM" patch.

Well this somewhat misleading imho...

None of the previous patches, including your, do nothing to fix the null
derefence bug and that is the *only* bug we care about ATM. With these
fixes drivers that do not call tpm_chip_bootstrap() will be fully
working still but without encryption.

There's five drivers which would require update for that:

drivers/char/tpm/tpm_ftpm_tee.c:        pvt_data->chip->flags |= TPM_CHIP_FLAG_TPM2;
drivers/char/tpm/tpm_i2c_nuvoton.c:             chip->flags |= TPM_CHIP_FLAG_TPM2;
drivers/char/tpm/tpm_ibmvtpm.c:         chip->flags |= TPM_CHIP_FLAG_TPM2;
drivers/char/tpm/tpm_tis_i2c_cr50.c:    chip->flags |= TPM_CHIP_FLAG_TPM2;
drivers/char/tpm/tpm_vtpm_proxy.c:              proxy_dev->chip->flags |= TPM_CHIP_FLAG_TPM2;


BR, Jarkko