Re: [PATCH 2/2] tpm: st33zp24: Validate locality read result

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Aug 13, 2026 at 11:30:32PM +0800, Ruoyu Wang wrote:
> check_locality() treats every nonzero transport return as success. SPI
> errors remain negative, while the I2C path can convert a negative write
> error through its byte-sized status variable. Either result is nonzero
> even though the TPM_ACCESS byte can remain unwritten, so indeterminate
> ACTIVE_LOCALITY and VALID bits can falsely report an active locality.
> 
> Require recv() to return exactly the requested byte before examining
> TPM_ACCESS. Transport errors and short reads now report an inactive
> locality, while successful reads retain the existing behavior.
> 
> This issue was found by a static analysis checker and confirmed by manual
> source review.
> 
> Fixes: 251a7b08213a ("TPM: STMicroelectronics ST33 I2C KERNEL 3.x")
> Signed-off-by: Ruoyu Wang <ruoyuw560@gmail.com>
> ---
>  drivers/char/tpm/st33zp24/st33zp24.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/char/tpm/st33zp24/st33zp24.c b/drivers/char/tpm/st33zp24/st33zp24.c
> index 898e8d01d26698..0e2deff94c3672 100644
> --- a/drivers/char/tpm/st33zp24/st33zp24.c
> +++ b/drivers/char/tpm/st33zp24/st33zp24.c
> @@ -106,10 +106,10 @@ static bool check_locality(struct tpm_chip *chip)
>  {
>  	struct st33zp24_dev *tpm_dev = dev_get_drvdata(&chip->dev);
>  	u8 data;
> -	u8 status;
> +	int status;
>  
>  	status = tpm_dev->ops->recv(tpm_dev->phy_id, TPM_ACCESS, &data, 1);
> -	if (status && (data &
> +	if (status == 1 && (data &
>  		(TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID)) ==
>  		(TPM_ACCESS_ACTIVE_LOCALITY | TPM_ACCESS_VALID))
>  		return true;
> -- 
> 2.51.0
> 

Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

BR, Jarkko