[PATCH v6 1/3] efi_loader: Add check for event log passed from firmware

[Heinrich Schuchardt]

On 11/26/21 06:00, Ruchika Gupta wrote:
> Platforms may have support to measure their initial firmware components
> and pass the event log to u-boot. The event log address can be passed
> in property tpm_event_log_addr and tpm_event_log_size of the tpm node.
> Platforms may choose their own specific mechanism to do so. A weak
> function is added to check if even log has been passed to u-boot
> from earlier firmware components. If available, the eventlog is parsed
> to check for its correctness and further event logs are appended to the
> passed log.
>
> Signed-off-by: Ruchika Gupta <ruchika.gupta at linaro.org>
> Tested-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> ---
> v6: No change
>
> v5:
> Shift the efi_init_event_log() to a different location in the file.
> This help fixes compilation issue introduced by calling efi_append_scrtm_version()
> from it.
>
> v4:
> Add SCRTM version to log only if previous firmware doesn't pass the eventlog
>
> v3:
> Return as soon as you detect error
>
> v2:
> Moved firmware eventlog code parsing to tcg2_get_fw_eventlog()
>
>   lib/efi_loader/efi_tcg2.c | 438 ++++++++++++++++++++++++++++++++------
>   1 file changed, 369 insertions(+), 69 deletions(-)
>
> diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
> index 8c1f22e337..a789c44660 100644
> --- a/lib/efi_loader/efi_tcg2.c
> +++ b/lib/efi_loader/efi_tcg2.c
> @@ -324,6 +324,45 @@ __weak efi_status_t platform_get_tpm2_device(struct udevice **dev)
>   	return EFI_NOT_FOUND;
>   }
>
> +/**
> + * platform_get_eventlog() - retrieve the eventlog address and size
> + *
> + * This function retrieves the eventlog address and size if the underlying
> + * firmware has done some measurements and passed them.
> + *
> + * This function may be overridden based on platform specific method of
> + * passing the eventlog address and size.
> + *
> + * @dev:	udevice
> + * @addr:	eventlog address
> + * @sz:		eventlog size
> + * Return:	status code
> + */
> +__weak efi_status_t platform_get_eventlog(struct udevice *dev, u64 *addr,
> +					  u32 *sz)

This function must be declared in a header to be overridden.

> +{
> +	const u64 *basep;
> +	const u32 *sizep;
> +
> +	basep = dev_read_prop(dev, "tpm_event_log_addr", NULL);
> +	if (!basep)
> +		return EFI_NOT_FOUND;
> +
> +	*addr = be64_to_cpup((__force __be64 *)basep);
> +
> +	sizep = dev_read_prop(dev, "tpm_event_log_size", NULL);
> +	if (!sizep)
> +		return EFI_NOT_FOUND;
> +
> +	*sz = be32_to_cpup((__force __be32 *)sizep);
> +	if (*sz == 0) {
> +		log_debug("event log empty\n");
> +		return EFI_NOT_FOUND;
> +	}
> +
> +	return EFI_SUCCESS;
> +}
> +
>   /**
>    * tpm2_get_max_command_size() - get the supported max command size
>    *
> @@ -1181,6 +1220,250 @@ static const struct efi_tcg2_protocol efi_tcg2_protocol = {
>   	.get_result_of_set_active_pcr_banks = efi_tcg2_get_result_of_set_active_pcr_banks,
>   };
>
> +/**
> + * parse_event_log_header() -  Parse and verify the event log header fields
> + *
> + * @buffer:			Pointer to the event header
> + * @size:			Size of the eventlog
> + * @pos:			Position in buffer after event log header
> + *
> + * Return:	status code
> + */
> +efi_status_t parse_event_log_header(void *buffer, u32 size, u32 *pos)

This function should be declared in a header or be static.

Should buffer have type struct tcg_pcr_event *?

> +{
> +	struct tcg_pcr_event *event_header = (struct tcg_pcr_event *)buffer;
> +	int i = 0;
> +
> +	if (size < sizeof(*event_header))
> +		return EFI_COMPROMISED_DATA;
> +
> +	if (get_unaligned_le32(&event_header->pcr_index) != 0 ||
> +	    get_unaligned_le32(&event_header->event_type) != EV_NO_ACTION)
> +		return EFI_COMPROMISED_DATA;
> +
> +	for (i = 0; i < sizeof(event_header->digest); i++) {
> +		if (event_header->digest[i] != 0)

if (event_header->digest[i])

> +			return EFI_COMPROMISED_DATA;
> +	}
> +
> +	*pos += sizeof(*event_header);

Do you re

> +
> +	return EFI_SUCCESS;
> +}
> +
> +/**
> + * parse_specid_event() -  Parse and verify the specID Event in the eventlog
> + *
> + * @dev:		udevice
> + * @buffer:		Pointer to the start of the eventlog
> + * @log_size:		Size of the eventlog
> + * @pos:		Offset in the evenlog where specID event starts
> + *
> + * Return:		status code
> + * @pos			Offset in the eventlog where the specID event ends

Duplicate line

> + * @digest_list:	list of digests in the event

Misplaced line

> + */
> +efi_status_t parse_specid_event(struct udevice *dev, void *buffer, u32 log_size,
> +				u32 *pos,
> +				struct tpml_digest_values *digest_list)
> +{

This function should be declared in a header or be static.

> +	struct tcg_efi_spec_id_event *spec_event;
> +	struct tcg_pcr_event *event_header = (struct tcg_pcr_event *)buffer;
> +	size_t spec_event_size;
> +	u32 active = 0, supported = 0, pcr_count = 0, alg_count = 0;
> +	u32 spec_active = 0;
> +	u16 hash_alg, hash_sz;
> +	u8 vendor_sz;
> +	int err, i;
> +
> +	/* Check specID event data */
> +	spec_event = (struct tcg_efi_spec_id_event *)((uintptr_t)buffer + *pos);
> +	/* Check for signature */
> +	if (memcmp(spec_event->signature, TCG_EFI_SPEC_ID_EVENT_SIGNATURE_03,
> +		   sizeof(TCG_EFI_SPEC_ID_EVENT_SIGNATURE_03))) {
> +		log_err("specID Event: Signature mismatch\n");
> +		return EFI_COMPROMISED_DATA;
> +	}
> +
> +	if (spec_event->spec_version_minor !=
> +			TCG_EFI_SPEC_ID_EVENT_SPEC_VERSION_MINOR_TPM2 ||
> +	    spec_event->spec_version_major !=
> +			TCG_EFI_SPEC_ID_EVENT_SPEC_VERSION_MAJOR_TPM2)
> +		return EFI_COMPROMISED_DATA;
> +
> +	if (spec_event->number_of_algorithms > MAX_HASH_COUNT ||
> +	    spec_event->number_of_algorithms < 1) {
> +		log_err("specID Event: Number of algorithms incorrect\n");
> +		return EFI_COMPROMISED_DATA;
> +	}
> +
> +	alg_count = spec_event->number_of_algorithms;
> +
> +	err = tpm2_get_pcr_info(dev, &supported, &active, &pcr_count);
> +	if (err)
> +		return EFI_DEVICE_ERROR;
> +
> +	digest_list->count = 0;
> +	/*
> +	 * We may need to worry about the order of algs in this structure as

%s/algs/algorithms/

> +	 * subsequent entries in event should be in same order

"We need to worry" sounds like a FIXME. Is there anything to fix or do
you mean:

We have to take care that the sequence of algorithms that we record in
digest_list matches the sequence in the event log.

> +	 */
> +	for (i = 0; i < alg_count; i++) {
> +		hash_alg =
> +		  get_unaligned_le16(&spec_event->digest_sizes[i].algorithm_id);
> +		hash_sz =
> +		   get_unaligned_le16(&spec_event->digest_sizes[i].digest_size);
> +
> +		if (!(supported & alg_to_mask(hash_alg))) {
> +			log_err("specID Event: Unsupported algorithm\n");
> +			return EFI_COMPROMISED_DATA;
> +		}
> +		digest_list->digests[digest_list->count++].hash_alg = hash_alg;
> +
> +		spec_active |= alg_to_mask(hash_alg);
> +	}
> +
> +	/* TCG spec expects the event log to have hashes for all active PCR's */

The TCG specification

> +	if (spec_active != active) {
> +		/*
> +		 * Previous stage bootloader should know all the active PCR's
> +		 * and use them in the Eventlog.
> +		 */
> +		log_err("specID Event: All active hash alg not present\n");
> +		return EFI_COMPROMISED_DATA;
> +	}
> +
> +	/*
> +	 * the size of the spec event and placement of vendor_info_size
> +	 * depends on supported algoriths
> +	 */
> +	spec_event_size =
> +		offsetof(struct tcg_efi_spec_id_event, digest_sizes) +
> +		alg_count * sizeof(spec_event->digest_sizes[0]);
> +
> +	vendor_sz = *(uint8_t *)((uintptr_t)buffer + *pos + spec_event_size);
> +
> +	spec_event_size += sizeof(vendor_sz) + vendor_sz;
> +	*pos += spec_event_size;
> +
> +	if (get_unaligned_le32(&event_header->event_size) != spec_event_size) {
> +		log_err("specID event: header event size mismatch\n");
> +		/* Right way to handle this can be to call SetActive PCR's */
> +		return EFI_COMPROMISED_DATA;
> +	}
> +
> +	return EFI_SUCCESS;
> +}
> +

Missing function description

> +efi_status_t tcg2_parse_event(struct udevice *dev, void *buffer, u32 log_size,
> +			      u32 *offset, struct tpml_digest_values *digest_list,
> +			      u32 *pcr)

Exported functions should be declared in a header.
Or should this function be static?

> +{
> +	struct tcg_pcr_event2 *event = NULL;
> +	u32 event_type, count, size, event_size;
> +	size_t pos;
> +
> +	if (*offset > log_size)
> +		return EFI_COMPROMISED_DATA;
> +
> +	event = (struct tcg_pcr_event2 *)((uintptr_t)buffer + *offset);
> +
> +	*pcr = get_unaligned_le32(&event->pcr_index);
> +
> +	event_size = tcg_event_final_size(digest_list);
> +
> +	if (*offset + event_size > log_size) {
> +		log_err("Event exceeds log size\n");
> +		return EFI_COMPROMISED_DATA;
> +	}
> +
> +	event_type = get_unaligned_le32(&event->event_type);
> +
> +	/* get the count */
> +	count = get_unaligned_le32(&event->digests.count);
> +	if (count != digest_list->count)
> +		return EFI_COMPROMISED_DATA;
> +
> +	pos = offsetof(struct tcg_pcr_event2, digests);
> +	pos += offsetof(struct tpml_digest_values, digests);
> +
> +	for (int i = 0; i < digest_list->count; i++) {
> +		u16 alg;
> +		u16 hash_alg = digest_list->digests[i].hash_alg;
> +		u8 *digest = (u8 *)&digest_list->digests[i].digest;
> +
> +		alg = get_unaligned_le16((void *)((uintptr_t)event + pos));
> +
> +		if (alg != hash_alg)
> +			return EFI_COMPROMISED_DATA;
> +
> +		pos += offsetof(struct tpmt_ha, digest);
> +		memcpy(digest, (void *)((uintptr_t)event + pos), alg_to_len(hash_alg));
> +		pos += alg_to_len(hash_alg);
> +	}
> +
> +	size = get_unaligned_le32((void *)((uintptr_t)event + pos));
> +	event_size += size;
> +	pos += sizeof(u32); /* tcg_pcr_event2 event_size*/
> +	pos += size;
> +
> +	/* make sure the calculated buffer is what we checked against */
> +	if (pos != event_size)
> +		return EFI_COMPROMISED_DATA;
> +
> +	if (pos > log_size)
> +		return EFI_COMPROMISED_DATA;
> +
> +	*offset += pos;
> +
> +	return EFI_SUCCESS;
> +}
> +

Missing function description.

> +efi_status_t tcg2_get_fw_eventlog(struct udevice *dev, void *log_buffer,
> +				  size_t *log_sz)

This function should be declared in a header or should be static.

> +{
> +	struct tpml_digest_values digest_list;
> +	void *buffer;
> +	efi_status_t ret;
> +	u32 pcr, pos;
> +	u64 base;
> +	u32 sz;
> +
> +	ret = platform_get_eventlog(dev, &base, &sz);
> +	if (ret != EFI_SUCCESS)
> +		return ret;
> +
> +	if (sz > TPM2_EVENT_LOG_SIZE)
> +		return EFI_VOLUME_FULL;
> +
> +	buffer = (void *)base;

Superfluous conversion.

> +	pos = 0;
> +	/* Parse the eventlog to check for its validity */
> +	ret = parse_event_log_header(buffer, sz, &pos);
> +	if (ret || pos > sz)

if (ret != EFI_SUCCESS

The check pos > sz should be done in the called function to avoid a
buffer overlow.

> +		return EFI_COMPROMISED_DATA;

Simply return ret.

> +
> +	ret = parse_specid_event(dev, buffer, sz, &pos, &digest_list);
> +	if (ret || pos > sz) {

ditto

> +		log_err("Error parsing SPEC ID Event\n");
> +		return EFI_COMPROMISED_DATA;
> +	}
> +
> +	while (pos < sz) {
> +		ret = tcg2_parse_event(dev, buffer, sz, &pos, &digest_list,
> +				       &pcr);
> +		if (ret) {
> +			log_err("Error parsing event\n");
> +			return ret;
> +		}
> +	}
> +
> +	memcpy(log_buffer, buffer, sz);
> +	*log_sz = sz;
> +
> +	return ret;
> +}
> +
>   /**
>    * create_specid_event() - Create the first event in the eventlog
>    *
> @@ -1312,69 +1595,6 @@ out:
>   	return ret;
>   }
>
> -/**
> - * efi_init_event_log() - initialize an eventlog
> - */
> -static efi_status_t efi_init_event_log(void)
> -{
> -	/*
> -	 * vendor_info_size is currently set to 0, we need to change the length
> -	 * and allocate the flexible array member if this changes
> -	 */
> -	struct tcg_pcr_event *event_header = NULL;
> -	struct udevice *dev;
> -	size_t spec_event_size;
> -	efi_status_t ret;
> -
> -	ret = platform_get_tpm2_device(&dev);
> -	if (ret != EFI_SUCCESS)
> -		goto out;
> -
> -	ret = efi_allocate_pool(EFI_BOOT_SERVICES_DATA, TPM2_EVENT_LOG_SIZE,
> -				(void **)&event_log.buffer);
> -	if (ret != EFI_SUCCESS)
> -		goto out;
> -
> -	/*
> -	 * initialize log area as 0xff so the OS can easily figure out the
> -	 * last log entry
> -	 */
> -	memset(event_log.buffer, 0xff, TPM2_EVENT_LOG_SIZE);
> -	event_log.pos = 0;
> -	event_log.last_event_size = 0;
> -	event_log.get_event_called = false;
> -	event_log.ebs_called = false;
> -	event_log.truncated = false;
> -
> -	/*
> -	 * The log header is defined to be in SHA1 event log entry format.
> -	 * Setup event header
> -	 */
> -	event_header =  (struct tcg_pcr_event *)event_log.buffer;
> -	put_unaligned_le32(0, &event_header->pcr_index);
> -	put_unaligned_le32(EV_NO_ACTION, &event_header->event_type);
> -	memset(&event_header->digest, 0, sizeof(event_header->digest));
> -	ret = create_specid_event(dev, (void *)((uintptr_t)event_log.buffer + sizeof(*event_header)),
> -				  &spec_event_size);
> -	if (ret != EFI_SUCCESS)
> -		goto free_pool;
> -	put_unaligned_le32(spec_event_size, &event_header->event_size);
> -	event_log.pos = spec_event_size + sizeof(*event_header);
> -	event_log.last_event_size = event_log.pos;
> -
> -	ret = create_final_event();
> -	if (ret != EFI_SUCCESS)
> -		goto free_pool;
> -
> -out:
> -	return ret;
> -
> -free_pool:
> -	efi_free_pool(event_log.buffer);
> -	event_log.buffer = NULL;
> -	return ret;
> -}
> -
>   /**
>    * tcg2_measure_event() - common function to add event log and extend PCR
>    *
> @@ -1427,6 +1647,92 @@ static efi_status_t efi_append_scrtm_version(struct udevice *dev)
>   	return ret;
>   }
>
> +/**
> + * efi_init_event_log() - initialize an eventlog

Please, add a line describing the return value.

> + */
> +static efi_status_t efi_init_event_log(void)
> +{
> +	/*
> +	 * vendor_info_size is currently set to 0, we need to change the length
> +	 * and allocate the flexible array member if this changes
> +	 */
> +	struct tcg_pcr_event *event_header = NULL;
> +	struct udevice *dev;
> +	size_t spec_event_size;
> +	efi_status_t ret;
> +
> +	ret = platform_get_tpm2_device(&dev);
> +	if (ret != EFI_SUCCESS)
> +		goto out;

return ret;

> +
> +	ret = efi_allocate_pool(EFI_BOOT_SERVICES_DATA, TPM2_EVENT_LOG_SIZE,
> +				(void **)&event_log.buffer);
> +	if (ret != EFI_SUCCESS)
> +		goto out;

return ret;

> +
> +	/*
> +	 * initialize log area as 0xff so the OS can easily figure out the
> +	 * last log entry

Where is this standardized?

EFI_TCG2_PROTOCOL.GetEventLog() returns EventLogLastEntry to indicate
the last log entry.

> +	 */
> +	memset(event_log.buffer, 0xff, TPM2_EVENT_LOG_SIZE);
> +
> +	/*
> +	 * The log header is defined to be in SHA1 event log entry format.
> +	 * Setup event header
> +	 */
> +	event_header =  (struct tcg_pcr_event *)event_log.buffer;
> +	event_log.pos = 0;
> +	event_log.last_event_size = 0;
> +	event_log.get_event_called = false;
> +	event_log.ebs_called = false;
> +	event_log.truncated = false;
> +
> +	/*
> +	 * Check if earlier firmware have passed any eventlog. Different
> +	 * platforms can use different ways to do so
> +	 */
> +	ret = tcg2_get_fw_eventlog(dev, event_log.buffer, &event_log.pos);
> +	/*
> +	 * If earlier firmware hasn't passed any eventlog, go ahead and
> +	 * create the eventlog header

%s/header/header./

> +	 */
> +	if (ret == EFI_NOT_FOUND) {
> +		put_unaligned_le32(0, &event_header->pcr_index);
> +		put_unaligned_le32(EV_NO_ACTION, &event_header->event_type);
> +		memset(&event_header->digest, 0, sizeof(event_header->digest));
> +		ret = create_specid_event(dev,
> +					  (void *)((uintptr_t)event_log.buffer +
> +						   sizeof(*event_header)),
> +					  &spec_event_size);
> +		if (ret != EFI_SUCCESS)
> +			goto free_pool;
> +		put_unaligned_le32(spec_event_size, &event_header->event_size);
> +		event_log.pos = spec_event_size + sizeof(*event_header);
> +		event_log.last_event_size = event_log.pos;
> +
> +		/*
> +		 * Add SCRTM version to the log if previous firmmware
> +		 * doesn't pass an eventlog
> +		 */
> +		ret = efi_append_scrtm_version(dev);
> +	}
> +
> +	if (ret != EFI_SUCCESS)
> +		goto free_pool;
> +
> +	ret = create_final_event();
> +	if (ret != EFI_SUCCESS)
> +		goto free_pool;
> +
> +out:
> +	return ret;

As you don't do anything here I would prefer removing the label out:

Best regards

Heinrich

> +
> +free_pool:
> +	efi_free_pool(event_log.buffer);
> +	event_log.buffer = NULL;
> +	return ret;
> +}
> +
>   /**
>    * tcg2_measure_variable() - add variable event log and extend PCR
>    *
> @@ -1963,12 +2269,6 @@ efi_status_t efi_tcg2_register(void)
>   	if (ret != EFI_SUCCESS)
>   		goto fail;
>
> -	ret = efi_append_scrtm_version(dev);
> -	if (ret != EFI_SUCCESS) {
> -		tcg2_uninit();
> -		goto fail;
> -	}
> -
>   	ret = efi_add_protocol(efi_root, &efi_guid_tcg2_protocol,
>   			       (void *)&efi_tcg2_protocol);
>   	if (ret != EFI_SUCCESS) {
>