Re: [v2] [PATCH 3/3] efi_loader: Extend PCR's for firmware measurements

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

On Tue, Nov 23, 2021 at 05:23:35PM +0530, Ruchika Gupta wrote:
> Firmwares before U-Boot may be capable of doing tpm measurements
> and passing them to U-Boot in the form of eventlog. However there
> may be scenarios where the firmwares don't have TPM driver and
> are not capable of extending the measurements in the PCRs.
> Based on TCG spec, if previous firnware has extended PCR's, PCR0
> would not be 0. So, read the PCR0 to determine if the PCR's need
> to be extended as eventlog is parsed or not.
> 
> Signed-off-by: Ruchika Gupta <ruchika.gupta@linaro.org>
> ---
> v2 : Removed check for PCR0 in eventlog
> 
>  lib/efi_loader/efi_tcg2.c | 77 +++++++++++++++++++++++++++++++++++++++
>  1 file changed, 77 insertions(+)
> 
> diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
> index c3ebdf92f5..133fe8291a 100644
> --- a/lib/efi_loader/efi_tcg2.c
> +++ b/lib/efi_loader/efi_tcg2.c
> @@ -199,6 +199,43 @@ static efi_status_t tcg2_pcr_extend(struct udevice *dev, u32 pcr_index,
>  	return EFI_SUCCESS;
>  }
>  
> +/* tcg2_pcr_read - Read PCRs for a TPM2 device for a given tpml_digest_values
> + *
> + * @dev:		device
> + * @digest_list:	list of digest algorithms to extend
> + *
> + * @Return: status code
> + */
> +static efi_status_t tcg2_pcr_read(struct udevice *dev, u32 pcr_index,
> +				  struct tpml_digest_values *digest_list)
> +{
> +	struct tpm_chip_priv *priv;
> +	unsigned int updates, pcr_select_min;
> +	u32 rc;
> +	size_t i;
> +
> +	priv = dev_get_uclass_priv(dev);
> +	if (!priv)
> +		return EFI_DEVICE_ERROR;
> +
> +	pcr_select_min = priv->pcr_select_min;
> +
> +	for (i = 0; i < digest_list->count; i++) {
> +		u16 hash_alg = digest_list->digests[i].hash_alg;
> +		u8 *digest = (u8 *)&digest_list->digests[i].digest;
> +
> +		rc = tpm2_pcr_read(dev, pcr_index, pcr_select_min,
> +				   hash_alg, digest, alg_to_len(hash_alg),
> +				   &updates);
> +		if (rc) {
> +			EFI_PRINT("Failed to read PCR\n");
> +			return EFI_DEVICE_ERROR;
> +		}
> +	}
> +
> +	return EFI_SUCCESS;
> +}
> +
>  /* put_event - Append an agile event to an eventlog
>   *
>   * @pcr_index:		PCR index
> @@ -1427,6 +1464,8 @@ efi_status_t tcg2_get_fw_eventlog(struct udevice *dev, void *log_buffer,
>  	u32 pcr, pos;
>  	u64 base;
>  	u32 sz;
> +	bool extend_pcr = false;
> +	int i;
>  
>  	ret = platform_get_eventlog(dev, &base, &sz);
>  	if (ret == EFI_SUCCESS) {
> @@ -1447,6 +1486,26 @@ efi_status_t tcg2_get_fw_eventlog(struct udevice *dev, void *log_buffer,
>  			return EFI_COMPROMISED_DATA;
>  		}
>  
> +		ret = tcg2_pcr_read(dev, 0, &digest_list);
> +		if (ret) {
> +			log_err("Error reading PCR 0\n");
> +			return ret;
> +		}
> +
> +		/*
> +		 * If PCR0 is 0, previous firmware didn't have the capability
> +		 * to extend the PCR. In this scenario, extend the PCR as
> +		 * the eventlog is parsed.
> +		 */
> +		for (i = 0; i < digest_list.count; i++) {
> +			u8 buffer[TPM2_DIGEST_LEN] =  { 0 };
> +			u16 hash_alg = digest_list.digests[i].hash_alg;
> +
> +			if (!memcmp((u8 *)&digest_list.digests[i].digest,
> +				    buffer, alg_to_len(hash_alg)))
> +				extend_pcr = true;
> +		}
> +
>  		while (pos < sz) {
>  			ret = tcg2_parse_event(dev, buffer, sz, &pos,
>  					       &digest_list, &pcr);
> @@ -1454,6 +1513,24 @@ efi_status_t tcg2_get_fw_eventlog(struct udevice *dev, void *log_buffer,
>  				log_err("Error parsing event\n");
>  				return ret;
>  			}
> +
> +			if (extend_pcr) {
> +				ret = tcg2_pcr_extend(dev, pcr, &digest_list);
> +				if (ret != EFI_SUCCESS) {
> +					log_err("Error in extending PCR\n");
> +					return ret;
> +				}
> +
> +				/* Clear the digest for next event */
> +				for (i = 0; i < digest_list.count; i++) {
> +					u16 hash_alg =
> +						digest_list.digests[i].hash_alg;
> +					u8 *digest =
> +					   (u8 *)&digest_list.digests[i].digest;
> +
> +					memset(digest, 0, alg_to_len(hash_alg));
> +				}
> +			}
>  		}
>  
>  		memcpy(log_buffer, buffer, sz);
> -- 
> 2.25.1
> 
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>