On 5/23/25 11:27 AM, Andrew Donnellan wrote:

On Wed, 2025-05-21 at 16:27 +0530, Srish Srinivasan wrote:

quoted

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-v<version>" or
"ibm,plpks-sb-v0" based on the key management mode, and return the
length of the secvar format property.

Co-developed-by: Souradeep <redacted>
Signed-off-by: Souradeep <redacted>
Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Nayna Jain <nayna@linux.ibm.com>

Thanks for the fixes, minor comment about the docs below.

Reviewed-by: Andrew Donnellan <redacted>

quoted

---
  Documentation/ABI/testing/sysfs-secvar        |  9 ++-
  arch/powerpc/platforms/pseries/plpks-secvar.c | 76 +++++++++++------
--
  2 files changed, 52 insertions(+), 33 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-secvar

b/Documentation/ABI/testing/sysfs-secvar
index 857cf12b0904..45281888e520 100644

--- a/Documentation/ABI/testing/sysfs-secvar
+++ b/Documentation/ABI/testing/sysfs-secvar

@@ -22,9 +22,12 @@ Description:	A string indicating which backend is

in use by the firmware.
  		and is expected to be "ibm,edk2-compat-v1".
  
  		On pseries/PLPKS, this is generated by the kernel
based on the
-		version number in the SB_VERSION variable in the
keystore, and
-		has the form "ibm,plpks-sb-v<version>", or
-		"ibm,plpks-sb-unknown" if there is no SB_VERSION
variable.
+		version number in the SB_VERSION variable in the
keystore. The
+		version numbering in the SB_VERSION variable starts
from 1. The
+		format string takes the form "ibm,plpks-sb-
v<version>" in the
+		case of dynamic key management mode. Otherwise, for
any error in
+		reading SB_VERSION it takes the form "ibm,plpks-sb-
v0",
+		indicating that the key management mode is static.

This last sentence is true, but makes it sound like static mode is only
used in case of errors.

Something like:

"If the SB_VERSION variable does not exist (or there is an error while
reading it), it takes the form "ibm,plpks-sb-v0", indicating that the
key management mode is static."

might be slightly clearer?

Hi Andrew,
Sure, will take this up in v3.

Thank You.

quoted

  
  What:		/sys/firmware/secvar/vars/<variable name>
  Date:		August 2019

diff --git a/arch/powerpc/platforms/pseries/plpks-secvar.c

b/arch/powerpc/platforms/pseries/plpks-secvar.c
index 257fd1f8bc19..767e5e8c6990 100644

--- a/arch/powerpc/platforms/pseries/plpks-secvar.c
+++ b/arch/powerpc/platforms/pseries/plpks-secvar.c

@@ -152,39 +152,55 @@ 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",
taking values
+ * starting from 1. It is owned by the Partition Firmware and its
presence
+ * indicates that the key management mode is dynamic. Any failure in
+ * reading SB_VERSION defaults the key management mode to static.
The error
+ * codes -ENOENT or -EPERM are expected in static key management
mode. An
+ * unexpected error code will have to be investigated. Only signed
variables
+ * have null bytes in their names, SB_VERSION does not.
+ *
+ * Return 0 to indicate that the key management mode is static.
Otherwise
+ * return the SB_VERSION value to indicate that the key management
mode is
+ * dynamic.
+ */
+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) {
+		if (rc != -ENOENT && rc != -EPERM)
+			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 of either
+ * "ibm,plpks-sb-v<n>" 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)