[PATCH 4/5] efi_capsule: Add a weak function to get the public key needed for capsule authentication

[Sughosh Ganu]

Define a weak function which would be used in the scenario where the
public key is stored on the platform's dtb. This dtb is concatenated
with the u-boot binary during the build process. Platforms which have
a different mechanism for getting the public key would define their
own platform specific function.

Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org>
---
 lib/efi_loader/efi_capsule.c | 38 ++++++++++++++++++++++++++++++++----
 1 file changed, 34 insertions(+), 4 deletions(-)

diff --git a/lib/efi_loader/efi_capsule.c b/lib/efi_loader/efi_capsule.c
index 1423b675c8..fc5e1c0856 100644
--- a/lib/efi_loader/efi_capsule.c
+++ b/lib/efi_loader/efi_capsule.c
@@ -14,10 +14,13 @@
 #include <mapmem.h>
 #include <sort.h>
 
+#include <asm/global_data.h>
 #include <crypto/pkcs7.h>
 #include <crypto/pkcs7_parser.h>
 #include <linux/err.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 const efi_guid_t efi_guid_capsule_report = EFI_CAPSULE_REPORT_GUID;
 static const efi_guid_t efi_guid_firmware_management_capsule_id =
 		EFI_FIRMWARE_MANAGEMENT_CAPSULE_ID_GUID;
@@ -210,11 +213,38 @@ const efi_guid_t efi_guid_capsule_root_cert_guid =
 
 __weak int efi_get_public_key_data(void **pkey, efi_uintn_t *pkey_len)
 {
-	/* The platform is supposed to provide
-	 * a method for getting the public key
-	 * stored in the form of efi signature
-	 * list
+	/*
+	 * This is a function for retrieving the public key from the
+	 * platform's device tree. The platform's device tree has been
+	 * concatenated with the u-boot binary.
+	 * If a platform has a different mechanism to get the public
+	 * key, it can define it's own function.
 	 */
+	const void *fdt_blob = gd->fdt_blob;
+	const void *blob;
+	const char *cnode_name = "capsule-key";
+	const char *snode_name = "signature";
+	int sig_node;
+	int len;
+
+	sig_node = fdt_subnode_offset(fdt_blob, 0, snode_name);
+	if (sig_node < 0) {
+		EFI_PRINT("Unable to get signature node offset\n");
+		return -FDT_ERR_NOTFOUND;
+	}
+
+	blob = fdt_getprop(fdt_blob, sig_node, cnode_name, &len);
+
+	if (!blob || len < 0) {
+		EFI_PRINT("Unable to get capsule-key value\n");
+		*pkey = NULL;
+		*pkey_len = 0;
+		return -FDT_ERR_NOTFOUND;
+	}
+
+	*pkey = (void *)blob;
+	*pkey_len = len;
+
 	return 0;
 }
 
-- 
2.17.1