security/integrity: fix pointer to ESL data and its size on pseries

On PowerVM guest, variable data is prefixed with 8 bytes of timestamp.
Extract ESL by stripping off the timestamp before passing to ESL parser.

Fixes: 4b3e71e ("integrity/powerpc: Support loading keys from PLPKS")
Cc: stable@vger.kenrnel.org # v6.3
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Tested-by: Nageswara R Sastry <rnsastry@linux.ibm.com>
Acked-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230608120444.382527-1-nayna@linux.ibm.com

Author: naynajain

security/integrity/platform_certs/load_powerpc.c

@@ -15,6 +15,9 @@
 #include "keyring_handler.h"
 #include "../integrity.h"
 
+#define extract_esl(db, data, size, offset)	\
+	do { db = data + offset; size = size - offset; } while (0)
+
 /*
  * Get a certificate list blob from the named secure variable.
  *
@@ -55,8 +58,9 @@ static __init void *get_cert_list(u8 *key, unsigned long keylen, u64 *size)
  */
 static int __init load_powerpc_certs(void)
 {
-	void *db = NULL, *dbx = NULL;
-	u64 dbsize = 0, dbxsize = 0;
+	void *db = NULL, *dbx = NULL, *data = NULL;
+	u64 dsize = 0;
+	u64 offset = 0;
 	int rc = 0;
 	ssize_t len;
 	char buf[32];
@@ -74,38 +78,46 @@ static int __init load_powerpc_certs(void)
 		return -ENODEV;
 	}
 
+	if (strcmp("ibm,plpks-sb-v1", buf) == 0)
+		/* PLPKS authenticated variables ESL data is prefixed with 8 bytes of timestamp */
+		offset = 8;
+
 	/*
 	 * Get db, and dbx. They might not exist, so it isn't an error if we
 	 * can't get them.
 	 */
-	db = get_cert_list("db", 3, &dbsize);
-	if (!db) {
+	data = get_cert_list("db", 3, &dsize);
+	if (!data) {
 		pr_info("Couldn't get db list from firmware\n");
-	} else if (IS_ERR(db)) {
-		rc = PTR_ERR(db);
+	} else if (IS_ERR(data)) {
+		rc = PTR_ERR(data);
 		pr_err("Error reading db from firmware: %d\n", rc);
 		return rc;
 	} else {
-		rc = parse_efi_signature_list("powerpc:db", db, dbsize,
+		extract_esl(db, data, dsize, offset);
+
+		rc = parse_efi_signature_list("powerpc:db", db, dsize,
 					      get_handler_for_db);
 		if (rc)
 			pr_err("Couldn't parse db signatures: %d\n", rc);
-		kfree(db);
+		kfree(data);
 	}
 
-	dbx = get_cert_list("dbx", 4,  &dbxsize);
-	if (!dbx) {
+	data = get_cert_list("dbx", 4,  &dsize);
+	if (!data) {
 		pr_info("Couldn't get dbx list from firmware\n");
-	} else if (IS_ERR(dbx)) {
-		rc = PTR_ERR(dbx);
+	} else if (IS_ERR(data)) {
+		rc = PTR_ERR(data);
 		pr_err("Error reading dbx from firmware: %d\n", rc);
 		return rc;
 	} else {
-		rc = parse_efi_signature_list("powerpc:dbx", dbx, dbxsize,
+		extract_esl(dbx, data, dsize, offset);
+
+		rc = parse_efi_signature_list("powerpc:dbx", dbx, dsize,
 					      get_handler_for_dbx);
 		if (rc)
 			pr_err("Couldn't parse dbx signatures: %d\n", rc);
-		kfree(dbx);
+		kfree(data);
 	}
 
 	return rc;