[PATCH v3 1/3] vboot: add DTB policy for supporting multiple required conf keys

[Thirupathaiah Annapureddy]

Currently FIT image must be signed by all required conf keys. This means
Verified Boot fails if there is a signature verification failure
using any required key in U-Boot DTB.

This patch introduces a new policy in DTB that can be set to any required
conf key. This means if verified boot passes with one of the required
keys, U-Boot will continue the OS hand off.

There were prior attempts to address this:
https://lists.denx.de/pipermail/u-boot/2019-April/366047.html
The above patch was failing "make tests".
https://lists.denx.de/pipermail/u-boot/2020-January/396629.html

Signed-off-by: Thirupathaiah Annapureddy <thiruan at linux.microsoft.com>
Reviewed-by: Simon Glass <sjg at chromium.org>
---

Changes in v3:
- Replaced 'u-boot' with 'U-Boot' in commit message.
- Added an explicit print message to indicate that no required signature
was verified.

Changes in v2:
- Modify fit_config_verify_required_sigs() to process required-mode
policy variable in U-boot DTB.

 common/image-fit-sig.c | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/common/image-fit-sig.c b/common/image-fit-sig.c
index cc1967109e..5401d9411b 100644
--- a/common/image-fit-sig.c
+++ b/common/image-fit-sig.c
@@ -416,6 +416,10 @@ int fit_config_verify_required_sigs(const void *fit, int conf_noffset,
 {
 	int noffset;
 	int sig_node;
+	int verified = 0;
+	int reqd_sigs = 0;
+	bool reqd_policy_all = true;
+	const char *reqd_mode;
 
 	/* Work out what we need to verify */
 	sig_node = fdt_subnode_offset(sig_blob, 0, FIT_SIG_NODENAME);
@@ -425,6 +429,14 @@ int fit_config_verify_required_sigs(const void *fit, int conf_noffset,
 		return 0;
 	}
 
+	/* Get required-mode policy property from DTB */
+	reqd_mode = fdt_getprop(sig_blob, sig_node, "required-mode", NULL);
+	if (reqd_mode && !strcmp(reqd_mode, "any"))
+		reqd_policy_all = false;
+
+	debug("%s: required-mode policy set to '%s'\n", __func__,
+	      reqd_policy_all ? "all" : "any");
+
 	fdt_for_each_subnode(noffset, sig_blob, sig_node) {
 		const char *required;
 		int ret;
@@ -433,15 +445,29 @@ int fit_config_verify_required_sigs(const void *fit, int conf_noffset,
 				       NULL);
 		if (!required || strcmp(required, "conf"))
 			continue;
+
+		reqd_sigs++;
+
 		ret = fit_config_verify_sig(fit, conf_noffset, sig_blob,
 					    noffset);
 		if (ret) {
-			printf("Failed to verify required signature '%s'\n",
-			       fit_get_name(sig_blob, noffset, NULL));
-			return ret;
+			if (reqd_policy_all) {
+				printf("Failed to verify required signature '%s'\n",
+				       fit_get_name(sig_blob, noffset, NULL));
+				return ret;
+			}
+		} else {
+			verified++;
+			if (!reqd_policy_all)
+				break;
 		}
 	}
 
+	if (reqd_sigs && !verified) {
+		printf("Failed to verify 'any' of the required signature(s)\n");
+		return -EPERM;
+	}
+
 	return 0;
 }
 
-- 
2.25.2