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Message-ID: <c06c6a36356ce803654a441d4b8b2901b5f78007.camel@linux.ibm.com>
Date: Fri, 23 May 2025 15:57:08 +1000
From: Andrew Donnellan <ajd@...ux.ibm.com>
To: Srish Srinivasan <ssrish@...ux.ibm.com>, linux-integrity@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org
Cc: maddy@...ux.ibm.com, mpe@...erman.id.au, npiggin@...il.com,
christophe.leroy@...roup.eu, naveen@...nel.org, zohar@...ux.ibm.com,
nayna@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] powerpc/pseries: Correct secvar format
representation for static key management
On Wed, 2025-05-21 at 16:27 +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-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@...p.linux.ibm.com>
> Signed-off-by: Souradeep <soura@...p.linux.ibm.com>
> Signed-off-by: Srish Srinivasan <ssrish@...ux.ibm.com>
> Reviewed-by: Mimi Zohar <zohar@...ux.ibm.com>
> Reviewed-by: Stefan Berger <stefanb@...ux.ibm.com>
> Reviewed-by: Nayna Jain <nayna@...ux.ibm.com>
Thanks for the fixes, minor comment about the docs below.
Reviewed-by: Andrew Donnellan <ajd@...ux.ibm.com>
> ---
> Documentation/ABI/testing/sysfs-secvar | 9 ++-
> arch/powerpc/platforms/pseries/plpks-secvar.c | 76 +++++++++++------
> --
> 2 files changed, 52 insertions(+), 33 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-secvar
> b/Documentation/ABI/testing/sysfs-secvar
> index 857cf12b0904..45281888e520 100644
> --- a/Documentation/ABI/testing/sysfs-secvar
> +++ b/Documentation/ABI/testing/sysfs-secvar
> @@ -22,9 +22,12 @@ 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. Otherwise, for
> any error in
> + reading SB_VERSION it takes the form "ibm,plpks-sb-
> v0",
> + indicating that the key management mode is static.
This last sentence is true, but makes it sound like static mode is only
used in case of errors.
Something like:
"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."
might be slightly clearer?
>
> 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 257fd1f8bc19..767e5e8c6990 100644
> --- a/arch/powerpc/platforms/pseries/plpks-secvar.c
> +++ b/arch/powerpc/platforms/pseries/plpks-secvar.c
> @@ -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;
> - }
> - 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)
--
Andrew Donnellan OzLabs, ADL Canberra
ajd@...ux.ibm.com IBM Australia Limited
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