linux-kernel - [PATCH 1/3] powerpc/pseries: Correct secvar format representation for static key management

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Message-ID: <20250430090350.30023-2-ssrish@linux.ibm.com>
Date: Wed, 30 Apr 2025 14:33:48 +0530
From: Srish Srinivasan <ssrish@...ux.ibm.com>
To: linux-integrity@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Cc: maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
        christophe.leroy@...roup.eu, naveen@...nel.org, ajd@...ux.ibm.com,
        zohar@...ux.ibm.com, nayna@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: [PATCH 1/3] powerpc/pseries: Correct secvar format representation for static key management

On a PLPKS enabled PowerVM LPAR, the secvar format property for static
key management is misrepresented as "ibm,plpks-sb-unknown", creating
reason for confusion.

Static key management mode uses fixed, built-in keys. Dynamic key
management mode allows keys to be updated in production to handle
security updates without firmware rebuilds.

Define a function named plpks_get_sb_keymgmt_mode() to retrieve the
key management mode based on the existence of the SB_VERSION property
in the firmware.

Set the secvar format property to either "ibm,plpks-sb-v1" or
"ibm,plpks-sb-v0" based on the key management mode, and return the
length of the secvar format property.

Co-developed-by: Souradeep <soura@...p.linux.ibm.com>
Signed-off-by: Souradeep <soura@...p.linux.ibm.com>
Signed-off-by: Srish Srinivasan <ssrish@...ux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
---
 arch/powerpc/platforms/pseries/plpks-secvar.c | 70 +++++++++++--------
 1 file changed, 40 insertions(+), 30 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/plpks-secvar.c b/arch/powerpc/platforms/pseries/plpks-secvar.c
index 257fd1f8bc19..d57067a733ab 100644
--- a/arch/powerpc/platforms/pseries/plpks-secvar.c
+++ b/arch/powerpc/platforms/pseries/plpks-secvar.c
@@ -152,39 +152,49 @@ static int plpks_set_variable(const char *key, u64 key_len, u8 *data,
 	return rc;
 }
 
-// PLPKS dynamic secure boot doesn't give us a format string in the same way OPAL does.
-// Instead, report the format using the SB_VERSION variable in the keystore.
-// The string is made up by us, and takes the form "ibm,plpks-sb-v<n>" (or "ibm,plpks-sb-unknown"
-// if the SB_VERSION variable doesn't exist). Hypervisor defines the SB_VERSION variable as a
-// "1 byte unsigned integer value".
-static ssize_t plpks_secvar_format(char *buf, size_t bufsize)
+/*
+ * Return the key management mode.
+ *
+ * SB_VERSION is defined as a "1 byte unsigned integer value". It is owned by
+ * the Partition Firmware and its presence indicates that the key management
+ * mode is dynamic. Only signed variables have null bytes in their names.
+ * SB_VERSION does not.
+ *
+ * Return 1 to indicate that the key management mode is dynamic. Otherwise
+ * return 0, indicating that the key management mode is static.
+ */
+static u8 plpks_get_sb_keymgmt_mode(void)
 {
-	struct plpks_var var = {0};
-	ssize_t ret;
-	u8 version;
-
-	var.component = NULL;
-	// Only the signed variables have null bytes in their names, this one doesn't
-	var.name = "SB_VERSION";
-	var.namelen = strlen(var.name);
-	var.datalen = 1;
-	var.data = &version;
-
-	// Unlike the other vars, SB_VERSION is owned by firmware instead of the OS
-	ret = plpks_read_fw_var(&var);
-	if (ret) {
-		if (ret == -ENOENT) {
-			ret = snprintf(buf, bufsize, "ibm,plpks-sb-unknown");
-		} else {
-			pr_err("Error %ld reading SB_VERSION from firmware\n", ret);
-			ret = -EIO;
-		}
-		goto err;
+	u8 mode;
+	ssize_t rc;
+	struct plpks_var var = {
+		.component = NULL,
+		.name = "SB_VERSION",
+		.namelen = 10,
+		.datalen = 1,
+		.data = &mode,
+	};
+
+	rc = plpks_read_fw_var(&var);
+	if (rc) {
+		pr_info("Error %ld reading SB_VERSION from firmware\n", rc);
+		mode = 0;
 	}
+	return mode;
+}
 
-	ret = snprintf(buf, bufsize, "ibm,plpks-sb-v%hhu", version);
-err:
-	return ret;
+// PLPKS dynamic secure boot doesn't give us a format string in the same way
+// OPAL does. Instead, report the format using the SB_VERSION variable in the
+// keystore. The string, made up by us, takes the form "ibm,plpks-sb-v<n>".Set
+// the secvar format property to either "ibm,plpks-sb-v1" or "ibm,plpks-sb-v0",
+// based on the key management mode, and return the length of the secvar format
+// property.
+static ssize_t plpks_secvar_format(char *buf, size_t bufsize)
+{
+	u8 mode;
+
+	mode = plpks_get_sb_keymgmt_mode();
+	return snprintf(buf, bufsize, "ibm,plpks-sb-v%hhu", mode);
 }
 
 static int plpks_max_size(u64 *max_size)
-- 
2.47.1