Re: [PATCH v3 9/9] firmware: arm_scmi: Validate PCC shared memory signature

On Thu, 13 Aug 2026 12:33:04 +0100
Sudeep Holla <[email protected]> wrote:

> Validate the PCC shared memory signature when setting up an SCMI PCC
> channel.
> 
> Reject channels whose shared memory signature does not encode
> PCC_SIGNATURE combined with the PCC subspace ID, so misconfigured
> firmware is caught before the transport starts using the shared memory
> region.
> 
> Signed-off-by: Sudeep Holla <[email protected]>
Interesting there aren't more checks on this in the various PCC users.
Question for another day perhaps.

Seems correct to me.

Reviewed-by: Jonathan Cameron <[email protected]>

> ---
>  drivers/firmware/arm_scmi/transports/pcc.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/firmware/arm_scmi/transports/pcc.c b/drivers/firmware/arm_scmi/transports/pcc.c
> index 337d551e3ad8..0ead0ec77162 100644
> --- a/drivers/firmware/arm_scmi/transports/pcc.c
> +++ b/drivers/firmware/arm_scmi/transports/pcc.c
> @@ -623,8 +623,11 @@ static void rx_callback(struct mbox_client *cl, void *m)
>  }
>  
>  static int pcc_chan_validate_shmem(struct scmi_chan_info *cinfo,
> -				   struct scmi_pcc *smbox)
> +				   struct scmi_pcc *smbox, int ss_id)
>  {
> +	struct pcc_shared_mem __iomem *shmem = smbox->pchan->shmem;
> +	u32 valid_signature = ss_id + PCC_SIGNATURE;
> +
>  	if (smbox->pchan->shmem_size < SCMI_PCC_SHMEM_OVERHEAD ||
>  	    smbox->pchan->shmem_size - SCMI_PCC_SHMEM_OVERHEAD <
>  	    cinfo->max_msg_size) {
> @@ -632,6 +635,11 @@ static int pcc_chan_validate_shmem(struct scmi_chan_info *cinfo,
>  		return -ENOSPC;
>  	}
>  
> +	if (ioread32(&shmem->header.signature) != valid_signature) {
> +		dev_err(cinfo->dev, "invalid PCC shared memory signature\n");
> +		return -EINVAL;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -667,7 +675,7 @@ static int pcc_chan_setup(struct scmi_chan_info *cinfo, struct device *dev,
>  		return ret;
>  	}
>  
> -	ret = pcc_chan_validate_shmem(cinfo, smbox);
> +	ret = pcc_chan_validate_shmem(cinfo, smbox, ss_id);
>  	if (ret) {
>  		pcc_mbox_free_channel(smbox->pchan);
>  		return ret;
>