[PATCH v5 25/25] integrity/powerpc: Support loading keys from PLPKS

[Andrew Donnellan <ajd@linux.ibm.com>]

From: Russell Currey <ruscur@russell.cc>

Add support for loading keys from the PLPKS on pseries machines, with the
"ibm,plpks-sb-v1" format.

The object format is expected to be the same, so there shouldn't be any
functional differences between objects retrieved on powernv or pseries.

Unlike on powernv, on pseries the format string isn't contained in the
device tree. Use secvar_ops->format() to fetch the format string in a
generic manner, rather than searching the device tree ourselves.

(The current code searches the device tree for a node compatible with
"ibm,edk2-compat-v1". This patch switches to calling secvar_ops->format(),
which in the case of OPAL/powernv means opal_secvar_format(), which
searches the device tree for a node compatible with "ibm,secvar-backend"
and checks its "format" property. These are equivalent, as skiboot creates
a node with both "ibm,edk2-compat-v1" and "ibm,secvar-backend" as
compatible strings.)

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>

---

v3: New patch

v4: Pass format buffer size (stefanb, npiggin)

v5: Use sizeof(buf) rather than stating the size twice (npiggin)

    Clarify change to DT compatible strings in commit message (zohar)

    Reword commit message a bit (ajd)
---
 .../integrity/platform_certs/load_powerpc.c     | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/security/integrity/platform_certs/load_powerpc.c b/security/integrity/platform_certs/load_powerpc.c
index dee51606d5f4..b9de70b90826 100644
--- a/security/integrity/platform_certs/load_powerpc.c
+++ b/security/integrity/platform_certs/load_powerpc.c
@@ -10,7 +10,6 @@
 #include <linux/cred.h>
 #include <linux/err.h>
 #include <linux/slab.h>
-#include <linux/of.h>
 #include <asm/secure_boot.h>
 #include <asm/secvar.h>
 #include "keyring_handler.h"
@@ -59,16 +58,22 @@ static int __init load_powerpc_certs(void)
 	void *db = NULL, *dbx = NULL;
 	u64 dbsize = 0, dbxsize = 0;
 	int rc = 0;
-	struct device_node *node;
+	ssize_t len;
+	char buf[32];
 
 	if (!secvar_ops)
 		return -ENODEV;
 
-	/* The following only applies for the edk2-compat backend. */
-	node = of_find_compatible_node(NULL, NULL, "ibm,edk2-compat-v1");
-	if (!node)
+	len = secvar_ops->format(buf, sizeof(buf));
+	if (len <= 0)
 		return -ENODEV;
 
+	// Check for known secure boot implementations from OPAL or PLPKS
+	if (strcmp("ibm,edk2-compat-v1", buf) && strcmp("ibm,plpks-sb-v1", buf)) {
+		pr_err("Unsupported secvar implementation \"%s\", not loading certs\n", buf);
+		return -ENODEV;
+	}
+
 	/*
 	 * Get db, and dbx. They might not exist, so it isn't an error if we
 	 * can't get them.
@@ -103,8 +108,6 @@ static int __init load_powerpc_certs(void)
 		kfree(dbx);
 	}
 
-	of_node_put(node);
-
 	return rc;
 }
 late_initcall(load_powerpc_certs);
-- 
2.39.1