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powerpc/pseries: Correct secvar format representation for static key management

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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
This commit is contained in:
Srish Srinivasan 2025-06-11 02:49:05 +05:30 committed by Madhavan Srinivasan
parent 760b9b4f6d
commit fbf355f32b
2 changed files with 53 additions and 33 deletions
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10
Documentation/ABI/testing/sysfs-secvar
View File

@ -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

76
arch/powerpc/platforms/pseries/plpks-secvar.c
View File

@ -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".
/*
* 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)
{
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;
}
/*
* 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)
{
struct plpks_var var = {0};
ssize_t ret;
u8 version;
u8 mode;
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;
}
ret = snprintf(buf, bufsize, "ibm,plpks-sb-v%hhu", version);
err:
return ret;
mode = plpks_get_sb_keymgmt_mode();
return snprintf(buf, bufsize, "ibm,plpks-sb-v%hhu", mode);
}
static int plpks_max_size(u64 *max_size)