efi_loader: Extend PCR's for firmware measurements

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>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>

1 files changed, 76 insertions, 0 deletions

diff --git a/lib/efi_loader/efi_tcg2.c b/lib/efi_loader/efi_tcg2.c
index 4471479..5f71b18 100644
--- a/lib/efi_loader/efi_tcg2.c
+++ b/lib/efi_loader/efi_tcg2.c
@@ -199,6 +199,44 @@ 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
+ * @pcr_index:		PCR index
+ * @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
@@ -1458,6 +1496,8 @@ static 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)
@@ -1479,6 +1519,26 @@ static efi_status_t tcg2_get_fw_eventlog(struct udevice *dev, void *log_buffer,
 		return ret;
 	}
 
+	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 hash_buf[TPM2_SHA512_DIGEST_SIZE] = { 0 };
+		u16 hash_alg = digest_list.digests[i].hash_alg;
+
+		if (!memcmp((u8 *)&digest_list.digests[i].digest, hash_buf,
+			    alg_to_len(hash_alg)))
+			extend_pcr = true;
+	}
+
 	while (pos < sz) {
 		ret = tcg2_parse_event(dev, buffer, sz, &pos, &digest_list,
 				       &pcr);
@@ -1486,6 +1546,22 @@ static 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);