powerpc/pseries: Implement secvars for dynamic secure boot

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.
(Even when using bin_attributes, which can be larger than a single page,
sysfs only gives us one page's worth of write buffer at a time, and the
hypervisor does not expose an interface for partial writes.)

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>
[mpe: Add NLS dependency to fix build errors, squash fix from ajd]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20230210080401.345462-25-ajd@linux.ibm.com

3 files changed, 219 insertions, 2 deletions

diff --git a/arch/powerpc/platforms/pseries/Kconfig b/arch/powerpc/platforms/pseries/Kconfig
index e51d65969318..b481c5c8bae1 100644
--- a/arch/powerpc/platforms/pseries/Kconfig
+++ b/arch/powerpc/platforms/pseries/Kconfig
@@ -151,6 +151,7 @@ config IBMEBUS
 
 config PSERIES_PLPKS
 	depends on PPC_PSERIES
+	select NLS
 	bool
 	# PowerVM provides an isolated Platform Keystore (PKS) storage
 	# allocation for each LPAR with individually managed access
diff --git a/arch/powerpc/platforms/pseries/Makefile b/arch/powerpc/platforms/pseries/Makefile
index 92310202bdd7..20a0f3c3fe04 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-$(CONFIG_PPC_SECURE_BOOT)	+= plpks-secvar.o
 obj-$(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..f6c8888f4076
--- /dev/null
+++ b/arch/powerpc/platforms/pseries/plpks-secvar.c
@@ -0,0 +1,216 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+// Secure variable implementation using the PowerVM LPAR Platform KeyStore (PLPKS)
+//
+// Copyright 2022, 2023 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 <linux/nls.h>
+#include <asm/machdep.h>
+#include <asm/secvar.h>
+#include <asm/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 u32 get_policy(const char *name)
+{
+	if ((strcmp(name, "db") == 0) ||
+	    (strcmp(name, "dbx") == 0) ||
+	    (strcmp(name, "grubdb") == 0) ||
+	    (strcmp(name, "grubdbx") == 0) ||
+	    (strcmp(name, "sbat") == 0))
+		return (PLPKS_WORLDREADABLE | PLPKS_SIGNEDUPDATE);
+	else
+		return PLPKS_SIGNEDUPDATE;
+}
+
+static const char * const plpks_var_names[] = {
+	"PK",
+	"KEK",
+	"db",
+	"dbx",
+	"grubdb",
+	"grubdbx",
+	"sbat",
+	"moduledb",
+	"trustedcadb",
+	NULL,
+};
+
+static int plpks_get_variable(const char *key, u64 key_len, u8 *data,
+			      u64 *data_size)
+{
+	struct plpks_var var = {0};
+	int rc = 0;
+
+	// We subtract 1 from key_len because we don't need to include the
+	// null terminator at the end of the string
+	var.name = kcalloc(key_len - 1, sizeof(wchar_t), GFP_KERNEL);
+	if (!var.name)
+		return -ENOMEM;
+	rc = utf8s_to_utf16s(key, key_len - 1, UTF16_LITTLE_ENDIAN, (wchar_t *)var.name,
+			     key_len - 1);
+	if (rc < 0)
+		goto err;
+	var.namelen = rc * 2;
+
+	var.os = PLPKS_VAR_LINUX;
+	if (data) {
+		var.data = data;
+		var.datalen = *data_size;
+	}
+	rc = plpks_read_os_var(&var);
+
+	if (rc)
+		goto err;
+
+	*data_size = var.datalen;
+
+err:
+	kfree(var.name);
+	if (rc && rc != -ENOENT) {
+		pr_err("Failed to read variable '%s': %d\n", key, rc);
+		// Return -EIO since userspace probably doesn't care about the
+		// specific error
+		rc = -EIO;
+	}
+	return rc;
+}
+
+static int plpks_set_variable(const char *key, u64 key_len, u8 *data,
+			      u64 data_size)
+{
+	struct plpks_var var = {0};
+	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;
+
+	// We subtract 1 from key_len because we don't need to include the
+	// null terminator at the end of the string
+	var.name = kcalloc(key_len - 1, sizeof(wchar_t), GFP_KERNEL);
+	if (!var.name)
+		return -ENOMEM;
+	rc = utf8s_to_utf16s(key, key_len - 1, UTF16_LITTLE_ENDIAN, (wchar_t *)var.name,
+			     key_len - 1);
+	if (rc < 0)
+		goto err;
+	var.namelen = rc * 2;
+
+	memcpy(&flags, data, sizeof(flags));
+
+	var.datalen = data_size - sizeof(flags);
+	var.data = data + sizeof(flags);
+	var.os = PLPKS_VAR_LINUX;
+	var.policy = get_policy(key);
+
+	// Unlike in the read case, the plpks error code can be useful to
+	// userspace on write, so we return it rather than just -EIO
+	rc = plpks_signed_update_var(&var, flags);
+
+err:
+	kfree(var.name);
+	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)
+{
+	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;
+	}
+
+	ret = snprintf(buf, bufsize, "ibm,plpks-sb-v%hhu", version);
+err:
+	return ret;
+}
+
+static int plpks_max_size(u64 *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 = (u64)plpks_get_maxobjectsize() + sizeof(u64);
+
+	return 0;
+}
+
+
+static const struct secvar_operations plpks_secvar_ops = {
+	.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 int plpks_secvar_init(void)
+{
+	if (!plpks_is_available())
+		return -ENODEV;
+
+	return set_secvar_ops(&plpks_secvar_ops);
+}
+machine_device_initcall(pseries, plpks_secvar_init);