Re: [PATCH v2 1/1] tpm: reject duplicate PCR banks in tpm2_get_pcr_allocation

[Jarkko Sakkinen <jarkko@kernel.org>]

On Wed, Sep 30, 2026 at 12:25:06AM +0300, Jarkko Sakkinen wrote:
> On Mon, Sep 28, 2026 at 04:27:00PM +0800, Yuqi Xu wrote:
> > The TPM2_CAP_PCRS response is external input. tpm2_get_pcr_allocation()
> > adds every active selection to allocated_banks, while
> > tpm_sysfs_add_device() has one group slot per distinct hash algorithm.
> > Eight duplicate selections can therefore write past chip->groups[].
> > 
> > The TPM protocol does not allow a hash algorithm to appear twice in
> > this capability response. Treat a duplicate as a broken TPM and return
> > -EIO so the chip is not enabled, instead of silently dropping the
> > extra selection.
> > 
> > Fixes: aab73d952402 ("tpm: add sysfs exports for all banks of PCR registers")
> > Cc: stable@vger.kernel.org
> > Reported-by: Vega <vega@nebusec.ai>
> > Assisted-by: LLM
> > Signed-off-by: Yuqi Xu <xuyuqiabc@gmail.com>
> > Reviewed-by: Ren Wei <weir@nebusec.ai>
> > ---
> > Changes in v2:
> >  - Return -EIO on a duplicate PCR bank instead of silently ignoring
> >    it, as requested by Jarkko Sakkinen. A duplicate violates the TPM
> >    protocol, so the chip is not enabled.
> >  - v1 Link: https://lore.kernel.org/all/cover.1789800840.git.xuyuqiabc@gmail.com/
> >  drivers/char/tpm/tpm2-cmd.c | 18 ++++++++++++++++++
> >  1 file changed, 18 insertions(+)
> > 
> > diff --git a/drivers/char/tpm/tpm2-cmd.c b/drivers/char/tpm/tpm2-cmd.c
> > index ae22295df798..a94f4395c198 100644
> > --- a/drivers/char/tpm/tpm2-cmd.c
> > +++ b/drivers/char/tpm/tpm2-cmd.c
> > @@ -527,6 +527,7 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
> >  	u32 rsp_len;
> >  	int rc;
> >  	int i = 0;
> > +	int j;
> >  
> >  	struct tpm_buf *buf __free(kfree) = kzalloc(TPM_BUFSIZE, GFP_KERNEL);
> >  	if (!buf)
> > @@ -569,6 +570,23 @@ ssize_t tpm2_get_pcr_allocation(struct tpm_chip *chip)
> >  		pcr_select_offset = memchr_inv(pcr_selection.pcr_select, 0,
> >  					       pcr_selection.size_of_select);
> >  		if (pcr_select_offset) {
> > +			for (j = 0; j < nr_alloc_banks; j++) {
> > +				if (chip->allocated_banks[j].alg_id == hash_alg)
> > +					break;
> > +			}
> > +
> > +			/*
> > +			 * The TPM protocol does not allow the same hash
> > +			 * algorithm twice.  A duplicate means this device
> > +			 * is not behaving; do not enable it.
> > +			 */
> > +			if (j != nr_alloc_banks) {
> > +				pr_err("tpm: duplicate PCR bank for algorithm 0x%04x\n",
> > +				       hash_alg);
> > +				rc = -EIO;
> > +				break;
> > +			}
> > +
> >  			chip->allocated_banks[nr_alloc_banks].alg_id = hash_alg;
> >  
> >  			rc = tpm2_init_bank_info(chip, nr_alloc_banks);
> > -- 
> > 2.55.0
> > 
> 
> Yeah, so in some places like this some of the TPM driver code does
> return -EFAULT but I'd like to progressively refactor so that any
> corrupted traffic is always -EIO and use -EFAULT for memory related
> issues. 
> 
> Thank you!
> 
> Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

WARNING: Reported-by: should be immediately followed by Closes: or Link: with a URL to the report
#18:
Reported-by: Vega <vega@nebusec.ai>
Assisted-by: LLM

No need to resend a new version but I'd need a link to the *report* to
retain reported-by tag here.

Br, Jarkko