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-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 <soura@imap.linux.ibm.com>
Signed-off-by: Souradeep <soura@imap.linux.ibm.com>
Signed-off-by: Srish Srinivasan <ssrish@linux.ibm.com>
Tested-by: R Nageswara Sastry <rnsastry@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>
Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250610211907.101384-2-ssrish@linux.ibm.com

diff --git a/Documentation/ABI/testing/sysfs-secvar b/Documentation/ABI/testing/sysfs-secvar
index 857cf12b0904a51102844d0226bb31397b6f652a..f001a4f4bd2ebbe020a56ea04200aca8440f13d8 100644 (file)
--- a/Documentation/ABI/testing/sysfs-secvar
+++ b/Documentation/ABI/testing/sysfs-secvar
@@ -22,9 +22,13 @@ 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. 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.
 
 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 257fd1f8bc191b22e5342040d50191155d2f9db9..767e5e8c69900ba2fe28b48476004831e2d84a76 100644 (file)
--- a/arch/powerpc/platforms/pseries/plpks-secvar.c
+++ b/arch/powerpc/platforms/pseries/plpks-secvar.c
@@ -152,39 +152,55 @@ err:
        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)