On 6/4/25 10:11 PM, Michal Suchánek wrote:

On Thu, May 29, 2025 at 10:39:58PM +0530, Srish Srinivasan wrote:

quoted

On 5/23/25 11:49 AM, Michal Suchánek wrote:

quoted

Hello,

On Wed, May 21, 2025 at 04:27:58PM +0530, Srish Srinivasan wrote:

quoted

The PLPKS enabled PowerVM LPAR sysfs exposes all of the secure boot
secvars irrespective of the key management mode.

The PowerVM LPAR supports static and dynamic key management for secure
boot. The key management option can be updated in the management
console. Only in the dynamic key mode can the user modify the secure
boot secvars db, dbx, grubdb, grubdbx, and sbat, which are exposed via
the sysfs interface. But the sysfs interface exposes these secvars even
in the static key mode. This could lead to errors when reading them or
writing to them in the static key mode.

would it cause an error when reading these variables or only when
writing them?

Thanks

Michal

Hi Michal,
Thanks for taking a look.


Yes, when PKS is enabled without enabling dynamic key secure boot, the
secvars
are NOT yet initialized with the default keys built into the binaries, and
therefore
reading them will result in an error.

That suggests that 'cannot be written' as said in the documentation and
commit message, which would imply readonly, is misleading. The value is
not accessible at all.

Hi Michal.

Yes, this seems to be misleading.

Will address this.

quoted

Now, while in static key management mode with PKS enabled, if one tries to
populate secvars that are relevant to dynamic key management, the write does
not fail as long as the "Platform KeyStore Signed Update Infrastructure"
flag on
the HMC is enabled and the signed updates are authorized by valid PK/KEK
keys.

Which suggests that some variables can if fact be written

quoted

However, secvars like db and grubdb populated while in static key management
mode are not used by the Partition Firmware or grub as SB_VERSION is not
present,

but are not used until the key management is switched to dynamic

quoted

i.e dynamic key secure boot has not been enabled yet. In this case, when
there is a
transition from static key management to dynamic key management, secvars
with
the signed update policy bit set will not be overwritten by the hypervisor
with the
default keys. Now, if the keys written into these secvars were not the ones
that were
used to sign the grub and kernel, it would fail to verify them.

Which is the case even for the case the system is already in dynamic key
mode, unless the variables are append-only.

Yes, that is correct. The main intention of this patch is to not expose 
secvars that are

to be consumed only in the dynamic key management mode while in static key

management mode.


I will post v4 with the updated patch description and documentation.

Thanks

Michal

quoted

These are the reasons behind the decision to expose only those secvars that
are
relevant to the key management mode.

quoted

quoted

Expose only PK, trustedcadb, and moduledb in the static key mode to
enable loading of signed third-party kernel modules.

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>
Reviewed-by: Andrew Donnellan <redacted>
---
   Documentation/ABI/testing/sysfs-secvar        |  6 ++++
   arch/powerpc/platforms/pseries/plpks-secvar.c | 28 ++++++++++++++++---
   2 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-secvar b/Documentation/ABI/testing/sysfs-secvar
index 45281888e520..948df3446a03 100644
--- a/Documentation/ABI/testing/sysfs-secvar
+++ b/Documentation/ABI/testing/sysfs-secvar

@@ -37,6 +37,12 @@ Description:	Each secure variable is represented as a directory named as
   		representation. The data and size can be determined by reading
   		their respective attribute files.
+		Only secvars relevant to the key management mode are exposed.
+		Only in the dynamic key mode can the user modify the secure boot
+		secvars db, dbx, grubdb, grubdbx, and sbat. PK, trustedcadb and
+		moduledb are the secvars common to both static and dynamic key
+		management modes.
+
   What:		/sys/firmware/secvar/vars/<variable_name>/size
   Date:		August 2019
   Contact:	Nayna Jain <nayna@linux.ibm.com>

diff --git a/arch/powerpc/platforms/pseries/plpks-secvar.c b/arch/powerpc/platforms/pseries/plpks-secvar.c
index 767e5e8c6990..f9e9cc40c9d0 100644
--- a/arch/powerpc/platforms/pseries/plpks-secvar.c
+++ b/arch/powerpc/platforms/pseries/plpks-secvar.c

@@ -59,7 +59,14 @@ static u32 get_policy(const char *name)
   		return PLPKS_SIGNEDUPDATE;
   }
-static const char * const plpks_var_names[] = {
+static const char * const plpks_var_names_static[] = {
+	"PK",
+	"moduledb",
+	"trustedcadb",
+	NULL,
+};
+
+static const char * const plpks_var_names_dynamic[] = {
   	"PK",
   	"KEK",
   	"db",

@@ -213,21 +220,34 @@ static int plpks_max_size(u64 *max_size)
   	return 0;
   }
+static const struct secvar_operations plpks_secvar_ops_static = {
+	.get = plpks_get_variable,
+	.set = plpks_set_variable,
+	.format = plpks_secvar_format,
+	.max_size = plpks_max_size,
+	.config_attrs = config_attrs,
+	.var_names = plpks_var_names_static,
+};
-static const struct secvar_operations plpks_secvar_ops = {
+static const struct secvar_operations plpks_secvar_ops_dynamic = {
   	.get = plpks_get_variable,
   	.set = plpks_set_variable,
   	.format = plpks_secvar_format,
   	.max_size = plpks_max_size,
   	.config_attrs = config_attrs,
-	.var_names = plpks_var_names,
+	.var_names = plpks_var_names_dynamic,
   };
   static int plpks_secvar_init(void)
   {
+	u8 mode;
+
   	if (!plpks_is_available())
   		return -ENODEV;
-	return set_secvar_ops(&plpks_secvar_ops);
+	mode = plpks_get_sb_keymgmt_mode();
+	if (mode)
+		return set_secvar_ops(&plpks_secvar_ops_dynamic);
+	return set_secvar_ops(&plpks_secvar_ops_static);
   }
   machine_device_initcall(pseries, plpks_secvar_init);

-- 
2.47.1