[PATCH v2 7/7] powerpc/pseries: Implement secvars for dynamic secure boot

Russell Currey
2022-12-30T04:22:27Z

The pseries platform can support dynamic secure boot (i.e. secure boot
using user-defined keys) using variables contained with the PowerVM LPAR
Platform KeyStore (PLPKS). Using the powerpc secvar API, expose the
relevant variables for pseries dynamic secure boot through the existing
secvar filesystem layout.

The relevant variables for dynamic secure boot are signed in the
keystore, and can only be modified using the H_PKS_SIGNED_UPDATE hcall.
Object labels in the keystore are encoded using ucs2 format. With our
fixed variable names we don't have to care about encoding outside of the
necessary byte padding.

When a user writes to a variable, the first 8 bytes of data must contain
the signed update flags as defined by the hypervisor.

When a user reads a variable, the first 4 bytes of data contain the
policies defined for the object.

Limitations exist due to the underlying implementation of sysfs binary
attributes, as is the case for the OPAL secvar implementation -
partial writes are unsupported and writes cannot be larger than PAGE_SIZE.

Co-developed-by: Nayna Jain <nayna@linux.ibm.com>
Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Co-developed-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Russell Currey <ruscur@russell.cc>
---
v2: Remove unnecessary config vars from sysfs and document the others,
thanks to review from Greg. If we end up needing to expose more, we
can add them later and update the docs.

Use sysfs_emit() instead of sprintf(), thanks to Greg.

Change the size of the sysfs binary attributes to include the 8-byte
flags header, preventing truncation of large writes.

Documentation/ABI/testing/sysfs-secvar | 67 ++++-
arch/powerpc/platforms/pseries/Kconfig | 13 +
arch/powerpc/platforms/pseries/Makefile | 4 +-
arch/powerpc/platforms/pseries/plpks-secvar.c | 245 ++++++++++++++++++
4 files changed, 326 insertions(+), 3 deletions(-)
create mode 100644 arch/powerpc/platforms/pseries/plpks-secvar.c

diff --git a/Documentation/ABI/testing/sysfs-secvar b/Documentation/ABI/testing/sysfs-secvar
index feebb8c57294..466a8cb92b92 100644
--- a/Documentation/ABI/testing/sysfs-secvar
+++ b/Documentation/ABI/testing/sysfs-secvar
@@ -34,7 +34,7 @@ Description: An integer representation of the size of the content of the

What: /sys/firmware/secvar/vars/<variable_name>/data
Date: August 2019
-Contact: Nayna Jain h<nayna@linux.ibm.com>
+Contact: Nayna Jain <nayna@linux.ibm.com>
Description: A read-only file containing the value of the variable. The size
of the file represents the maximum size of the variable data.

@@ -44,3 +44,68 @@ Contact: Nayna Jain <nayna@linux.ibm.com>
Description: A write-only file that is used to submit the new value for the
variable. The size of the file represents the maximum size of
the variable data that can be written.
+
+What: /sys/firmware/secvar/config
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: This optional directory contains read-only config attributes as
+ defined by the secure variable implementation. All data is in
+ ASCII format. The directory is only created if the backing
+ implementation provides variables to populate it, which at
+ present is only PLPKS on the pseries platform.
+
+What: /sys/firmware/secvar/config/version
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: RO file, only present if the secvar implementation is PLPKS.
+
+ Contains the config version as reported by the hypervisor in
+ ASCII decimal format.
+
+What: /sys/firmware/secvar/config/max_object_size
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: RO file, only present if the secvar implementation is PLPKS.
+
+ Contains the maximum allowed size of objects in the keystore
+ in bytes, represented in ASCII decimal format.
+
+ This is not necessarily the same as the max size that can be
+ written to an update file as writes can contain more than
+ object data, you should use the size of the update file for
+ that purpose.
+
+What: /sys/firmware/secvar/config/total_size
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: RO file, only present if the secvar implementation is PLPKS.
+
+ Contains the total size of the PLPKS in bytes, represented in
+ ASCII decimal format.
+
+What: /sys/firmware/secvar/config/used_space
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: RO file, only present if the secvar implementation is PLPKS.
+
+ Contains the current space consumed of the PLPKS in bytes,
+ represented in ASCII decimal format.
+
+What: /sys/firmware/secvar/config/supported_policies
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: RO file, only present if the secvar implementation is PLPKS.
+
+ Contains a bitmask of supported policy flags by the hypervisor,
+ represented as an 8 byte hexadecimal ASCII string. Consult the
+ hypervisor documentation for what these flags are.
+
+What: /sys/firmware/secvar/config/signed_update_algorithms
+Date: December 2022
+Contact: Nayna Jain <nayna@linux.ibm.com>
+Description: RO file, only present if the secvar implementation is PLPKS.
+
+ Contains a bitmask of flags indicating which algorithms the
+ hypervisor supports objects to be signed with when modifying
+ secvars, represented as a 16 byte hexadecimal ASCII string.
+ Consult the hypervisor documentation for what these flags mean.
diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index a3b4d99567cb..94e08c405d50 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -162,6 +162,19 @@ config PSERIES_PLPKS

If unsure, select N.

+config PSERIES_PLPKS_SECVAR
+ depends on PSERIES_PLPKS
+ depends on PPC_SECURE_BOOT
+ bool "Support for the PLPKS secvar interface"
+ help
+ PowerVM can support dynamic secure boot with user-defined keys
+ through the PLPKS. Keystore objects used in dynamic secure boot
+ can be exposed to the kernel and userspace through the powerpc
+ secvar infrastructure. Select this to enable the PLPKS backend
+ for secvars for use in pseries dynamic secure boot.
+
+ If unsure, select N.
+
config PAPR_SCM
depends on PPC_PSERIES && MEMORY_HOTPLUG && LIBNVDIMM
tristate "Support for the PAPR Storage Class Memory interface"
diff --git a/arch/powerpc/platforms/pseries/Makefile b/arch/powerpc/platforms/pseries/Makefile
index 92310202bdd7..807756991f9d 100644
--- a/arch/powerpc/platforms/pseries/Makefile
+++ b/arch/powerpc/platforms/pseries/Makefile
@@ -27,8 +27,8 @@ obj-$(CONFIG_PAPR_SCM) += papr_scm.o
obj-$(CONFIG_PPC_SPLPAR) += vphn.o
obj-$(CONFIG_PPC_SVM) += svm.o
obj-$(CONFIG_FA_DUMP) += rtas-fadump.o
-obj-$(CONFIG_PSERIES_PLPKS) += plpks.o
-
+obj-$(CONFIG_PSERIES_PLPKS) += plpks.o
+obj-$(CONFIG_PSERIES_PLPKS_SECVAR) += plpks-secvar.o
obj-$(CONFIG_SUSPEND) += suspend.o
obj-$(CONFIG_PPC_VAS) += vas.o vas-sysfs.o

diff --git a/arch/powerpc/platforms/pseries/plpks-secvar.c b/arch/powerpc/platforms/pseries/plpks-secvar.c
new file mode 100644
index 000000000000..8298f039bef4
--- /dev/null
+++ b/arch/powerpc/platforms/pseries/plpks-secvar.c
@@ -0,0 +1,245 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Secure variable implementation using the PowerVM LPAR Platform KeyStore (PLPKS)
+ *
+ * Copyright 2022, IBM Corporation
+ * Authors: Russell Currey
+ * Andrew Donnellan
+ * Nayna Jain
+ */
+
+#define pr_fmt(fmt) "secvar: "fmt
+
+#include <linux/printk.h>
+#include <linux/init.h>
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/kobject.h>
+#include <asm/secvar.h>
+#include "plpks.h"
+
+// Config attributes for sysfs
+#define PLPKS_CONFIG_ATTR(name, fmt, func) \
+ static ssize_t name##_show(struct kobject *kobj, \
+ struct kobj_attribute *attr, \
+ char *buf) \
+ { \
+ return sysfs_emit(buf, fmt, func()); \
+ } \
+ static struct kobj_attribute attr_##name = __ATTR_RO(name)
+
+PLPKS_CONFIG_ATTR(version, "%u\n", plpks_get_version);
+PLPKS_CONFIG_ATTR(max_object_size, "%u\n", plpks_get_maxobjectsize);
+PLPKS_CONFIG_ATTR(total_size, "%u\n", plpks_get_totalsize);
+PLPKS_CONFIG_ATTR(used_space, "%u\n", plpks_get_usedspace);
+PLPKS_CONFIG_ATTR(supported_policies, "%08x\n", plpks_get_supportedpolicies);
+PLPKS_CONFIG_ATTR(signed_update_algorithms, "%016llx\n", plpks_get_signedupdatealgorithms);
+
+static const struct attribute *config_attrs[] = {
+ &attr_version.attr,
+ &attr_max_object_size.attr,
+ &attr_total_size.attr,
+ &attr_used_space.attr,
+ &attr_supported_policies.attr,
+ &attr_signed_update_algorithms.attr,
+ NULL,
+};
+
+static u16 get_ucs2name(const char *name, uint8_t **ucs2_name)
+{
+ int namelen = strlen(name) * 2;
+ *ucs2_name = kzalloc(namelen, GFP_KERNEL);
+
+ if (!*ucs2_name)
+ return 0;
+
+ for (int i = 0; name[i]; i++) {
+ (*ucs2_name)[i * 2] = name[i];
+ (*ucs2_name)[i * 2 + 1] = '\0';
+ }
+
+ return namelen;
+}
+
+static u32 get_policy(const char *name)
+{
+ if ((strcmp(name, "db") == 0) ||
+ (strcmp(name, "dbx") == 0) ||
+ (strcmp(name, "grubdb") == 0) ||
+ (strcmp(name, "sbat") == 0))
+ return (WORLDREADABLE | SIGNEDUPDATE);
+ else
+ return SIGNEDUPDATE;
+}
+
+#define PLPKS_SECVAR_COUNT 8
+static char *var_names[PLPKS_SECVAR_COUNT] = {
+ "PK",
+ "KEK",
+ "db",
+ "dbx",
+ "grubdb",
+ "sbat",
+ "moduledb",
+ "trustedcadb",
+};
+
+static int plpks_get_variable(const char *key, uint64_t key_len,
+ u8 *data, uint64_t *data_size)
+{
+ struct plpks_var var = {0};
+ u16 ucs2_namelen;
+ u8 *ucs2_name;
+ int rc = 0;
+
+ ucs2_namelen = get_ucs2name(key, &ucs2_name);
+ if (!ucs2_namelen)
+ return -ENOMEM;
+
+ var.name = ucs2_name;
+ var.namelen = ucs2_namelen;
+ var.os = PLPKS_VAR_LINUX;
+ rc = plpks_read_os_var(&var);
+
+ if (rc)
+ goto err;
+
+ *data_size = var.datalen + sizeof(var.policy);
+
+ // We can be called with data = NULL to just get the object size.
+ if (data) {
+ memcpy(data, &var.policy, sizeof(var.policy));
+ memcpy(data + sizeof(var.policy), var.data, var.datalen);
+ }
+
+ kfree(var.data);
+err:
+ kfree(ucs2_name);
+ return rc;
+}
+
+static int plpks_set_variable(const char *key, uint64_t key_len,
+ u8 *data, uint64_t data_size)
+{
+ struct plpks_var var = {0};
+ u16 ucs2_namelen;
+ u8 *ucs2_name;
+ int rc = 0;
+ u64 flags;
+
+ // Secure variables need to be prefixed with 8 bytes of flags.
+ // We only want to perform the write if we have at least one byte of data.
+ if (data_size <= sizeof(flags))
+ return -EINVAL;
+
+ ucs2_namelen = get_ucs2name(key, &ucs2_name);
+ if (!ucs2_namelen)
+ return -ENOMEM;
+
+ memcpy(&flags, data, sizeof(flags));
+
+ var.datalen = data_size - sizeof(flags);
+ var.data = kzalloc(var.datalen, GFP_KERNEL);
+ if (!var.data) {
+ rc = -ENOMEM;
+ goto err;
+ }
+
+ memcpy(var.data, data + sizeof(flags), var.datalen);
+
+ var.name = ucs2_name;
+ var.namelen = ucs2_namelen;
+ var.os = PLPKS_VAR_LINUX;
+ var.policy = get_policy(key);
+
+ rc = plpks_signed_update_var(var, flags);
+
+ kfree(var.data);
+err:
+ kfree(ucs2_name);
+ return rc;
+}
+
+/*
+ * get_next() in the secvar API is designed for the OPAL API.
+ * If *key is 0, it returns the first variable in the keystore.
+ * Otherwise, you pass the name of a key and it returns next in line.
+ *
+ * We're going to cheat here - since we have fixed keys and don't care about
+ * key_len, we can just use it as an index.
+ */
+static int plpks_get_next_variable(const char *key, uint64_t *key_len, uint64_t keybufsize)
+{
+ if (!key || !key_len)
+ return -EINVAL;
+
+ if (*key_len >= PLPKS_SECVAR_COUNT)
+ return -ENOENT;
+
+ if (strscpy((char *)key, var_names[(*key_len)++], keybufsize) < 0)
+ return -E2BIG;
+
+ return 0;
+}
+
+// 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.
+static ssize_t plpks_secvar_format(char *buf)
+{
+ struct plpks_var var = {0};
+ ssize_t ret;
+
+ var.component = NULL;
+ // Only the signed variables have ucs2-encoded names, this one doesn't
+ var.name = "SB_VERSION";
+ var.namelen = 10;
+ var.datalen = 0;
+ var.data = NULL;
+
+ // 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)
+ return sysfs_emit(buf, "ibm,plpks-sb-unknown\n");
+
+ pr_err("Error %ld reading SB_VERSION from firmware\n", ret);
+ return ret;
+ }
+
+ // Hypervisor defines SB_VERSION as a "1 byte unsigned integer value"
+ ret = sysfs_emit(buf, "ibm,plpks-sb-%hhu\n", var.data[0]);
+
+ kfree(var.data);
+ return ret;
+}
+
+static int plpks_max_size(uint64_t *max_size)
+{
+ // The max object size reported by the hypervisor is accurate for the
+ // object itself, but we use the first 8 bytes of data on write as the
+ // signed update flags, so the max size a user can write is larger.
+ *max_size = (uint64_t)plpks_get_maxobjectsize() + 8;
+
+ return 0;
+}
+
+
+static const struct secvar_operations plpks_secvar_ops = {
+ .get = plpks_get_variable,
+ .get_next = plpks_get_next_variable,
+ .set = plpks_set_variable,
+ .format = plpks_secvar_format,
+ .max_size = plpks_max_size,
+};
+
+static int plpks_secvar_init(void)
+{
+ if (!plpks_is_available())
+ return -ENODEV;
+
+ set_secvar_ops(&plpks_secvar_ops);
+ set_secvar_config_attrs(config_attrs);
+ return 0;
+}
+device_initcall(plpks_secvar_init);
--
2.38.1