Commit fbf355f3 authored by Srish Srinivasan's avatar Srish Srinivasan Committed by Madhavan Srinivasan
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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: default avatarSouradeep <soura@imap.linux.ibm.com>
Signed-off-by: default avatarSouradeep <soura@imap.linux.ibm.com>
Signed-off-by: default avatarSrish Srinivasan <ssrish@linux.ibm.com>
Tested-by: default avatarR Nageswara Sastry <rnsastry@linux.ibm.com>
Reviewed-by: default avatarMimi Zohar <zohar@linux.ibm.com>
Reviewed-by: default avatarStefan Berger <stefanb@linux.ibm.com>
Reviewed-by: default avatarNayna Jain <nayna@linux.ibm.com>
Reviewed-by: default avatarAndrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: default avatarMadhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20250610211907.101384-2-ssrish@linux.ibm.com
parent 760b9b4f

Documentation/ABI/testing/sysfs-secvar

+7 −3
Original line number Diff line number Diff line
@@ -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

arch/powerpc/platforms/pseries/plpks-secvar.c

+46 −30
Original line number Diff line number Diff line
@@ -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;

	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;

	}

		goto err;

	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)