[PATCH v6 3/3] efi_loader: Extend PCR's for firmware measurements

[Ruchika Gupta]

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 at linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
v6: Changed TPM2_DIGEST_LEN to TPM2_SHA512_DIGEST_SIZE

v5 : No change

v4 : No change

v3 : 
Rebase changes on top of changes made in first patch series

v2 : 
Removed check for PCR0 in eventlog

 lib/efi_loader/efi_tcg2.c | 75 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
index a789c44660..295070f3d8 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
@@ -1428,6 +1465,8 @@ 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)
@@ -1449,6 +1488,26 @@ 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_SHA512_DIGEST_SIZE] =  { 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);
@@ -1456,6 +1515,22 @@ 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