On Wed, 2025-04-30 at 14:33 +0530, Srish Srinivasan wrote:
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 <so...@imap.linux.ibm.com>
Signed-off-by: Souradeep <so...@imap.linux.ibm.com>
Signed-off-by: Srish Srinivasan <ssr...@linux.ibm.com>
Reviewed-by: Mimi Zohar <zo...@linux.ibm.com>
Reviewed-by: Stefan Berger <stef...@linux.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.
+ */
This description isn't accurate.
For dynamic mode, it doesn't return 1, it returns whatever version is
defined in SB_VERSION, which could be 1, or could at some later point be
a higher version.
Which makes the function name a bit of a misnomer too - it is returning
the version number, just the version number can now be zero.
+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);
We need to check for -ENOENT, otherwise this message is going to be
printed every time you boot a machine in static mode.
I think you should handle this as the existing code does: if it's
ENOENT, return 0, and for other codes print an error and return -EIO.
+ 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);
It might be better to use something like "ibm,plpks-sb-static" in place
of "ibm,plpks-sb-v0" to make it instantly clear that static mode
doesn't use the same version numbering scheme as dynamic mode.
