powerpc: expose secure variables to userspace via sysfs

PowerNV secure variables, which store the keys used for OS kernel
verification, are managed by the firmware. These secure variables need to
be accessed by the userspace for addition/deletion of the certificates.

This patch adds the sysfs interface to expose secure variables for PowerNV
secureboot. The users shall use this interface for manipulating
the keys stored in the secure variables.

Signed-off-by: Nayna Jain <nayna@linux.ibm.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Eric Richter <erichte@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1573441836-3632-3-git-send-email-nayna@linux.ibm.com

2 files changed, 249 insertions, 0 deletions

diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 3cf26427334f..b216e9f316ee 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -162,6 +162,7 @@ obj-y				+= ucall.o
 endif
 
 obj-$(CONFIG_PPC_SECURE_BOOT)	+= secure_boot.o ima_arch.o secvar-ops.o
+obj-$(CONFIG_PPC_SECVAR_SYSFS)	+= secvar-sysfs.o
 
 # Disable GCOV, KCOV & sanitizers in odd or sensitive code
 GCOV_PROFILE_prom_init.o := n
diff --git a/arch/powerpc/kernel/secvar-sysfs.c b/arch/powerpc/kernel/secvar-sysfs.c
new file mode 100644
index 000000000000..a0a78aba2083
--- /dev/null
+++ b/arch/powerpc/kernel/secvar-sysfs.c
@@ -0,0 +1,248 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2019 IBM Corporation <nayna@linux.ibm.com>
+ *
+ * This code exposes secure variables to user via sysfs
+ */
+
+#define pr_fmt(fmt) "secvar-sysfs: "fmt
+
+#include <linux/slab.h>
+#include <linux/compat.h>
+#include <linux/string.h>
+#include <linux/of.h>
+#include <asm/secvar.h>
+
+#define NAME_MAX_SIZE	   1024
+
+static struct kobject *secvar_kobj;
+static struct kset *secvar_kset;
+
+static ssize_t format_show(struct kobject *kobj, struct kobj_attribute *attr,
+			   char *buf)
+{
+	ssize_t rc = 0;
+	struct device_node *node;
+	const char *format;
+
+	node = of_find_compatible_node(NULL, NULL, "ibm,secvar-backend");
+	if (!of_device_is_available(node))
+		return -ENODEV;
+
+	rc = of_property_read_string(node, "format", &format);
+	if (rc)
+		return rc;
+
+	rc = sprintf(buf, "%s\n", format);
+
+	of_node_put(node);
+
+	return rc;
+}
+
+
+static ssize_t size_show(struct kobject *kobj, struct kobj_attribute *attr,
+			 char *buf)
+{
+	uint64_t dsize;
+	int rc;
+
+	rc = secvar_ops->get(kobj->name, strlen(kobj->name) + 1, NULL, &dsize);
+	if (rc) {
+		pr_err("Error retrieving %s variable size %d\n", kobj->name,
+		       rc);
+		return rc;
+	}
+
+	return sprintf(buf, "%llu\n", dsize);
+}
+
+static ssize_t data_read(struct file *filep, struct kobject *kobj,
+			 struct bin_attribute *attr, char *buf, loff_t off,
+			 size_t count)
+{
+	uint64_t dsize;
+	char *data;
+	int rc;
+
+	rc = secvar_ops->get(kobj->name, strlen(kobj->name) + 1, NULL, &dsize);
+	if (rc) {
+		pr_err("Error getting %s variable size %d\n", kobj->name, rc);
+		return rc;
+	}
+	pr_debug("dsize is %llu\n", dsize);
+
+	data = kzalloc(dsize, GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	rc = secvar_ops->get(kobj->name, strlen(kobj->name) + 1, data, &dsize);
+	if (rc) {
+		pr_err("Error getting %s variable %d\n", kobj->name, rc);
+		goto data_fail;
+	}
+
+	rc = memory_read_from_buffer(buf, count, &off, data, dsize);
+
+data_fail:
+	kfree(data);
+	return rc;
+}
+
+static ssize_t update_write(struct file *filep, struct kobject *kobj,
+			    struct bin_attribute *attr, char *buf, loff_t off,
+			    size_t count)
+{
+	int rc;
+
+	pr_debug("count is %ld\n", count);
+	rc = secvar_ops->set(kobj->name, strlen(kobj->name) + 1, buf, count);
+	if (rc) {
+		pr_err("Error setting the %s variable %d\n", kobj->name, rc);
+		return rc;
+	}
+
+	return count;
+}
+
+static struct kobj_attribute format_attr = __ATTR_RO(format);
+
+static struct kobj_attribute size_attr = __ATTR_RO(size);
+
+static struct bin_attribute data_attr = __BIN_ATTR_RO(data, 0);
+
+static struct bin_attribute update_attr = __BIN_ATTR_WO(update, 0);
+
+static struct bin_attribute *secvar_bin_attrs[] = {
+	&data_attr,
+	&update_attr,
+	NULL,
+};
+
+static struct attribute *secvar_attrs[] = {
+	&size_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group secvar_attr_group = {
+	.attrs = secvar_attrs,
+	.bin_attrs = secvar_bin_attrs,
+};
+__ATTRIBUTE_GROUPS(secvar_attr);
+
+static struct kobj_type secvar_ktype = {
+	.sysfs_ops	= &kobj_sysfs_ops,
+	.default_groups = secvar_attr_groups,
+};
+
+static int update_kobj_size(void)
+{
+
+	struct device_node *node;
+	u64 varsize;
+	int rc = 0;
+
+	node = of_find_compatible_node(NULL, NULL, "ibm,secvar-backend");
+	if (!of_device_is_available(node)) {
+		rc = -ENODEV;
+		goto out;
+	}
+
+	rc = of_property_read_u64(node, "max-var-size", &varsize);
+	if (rc)
+		goto out;
+
+	data_attr.size = varsize;
+	update_attr.size = varsize;
+
+out:
+	of_node_put(node);
+
+	return rc;
+}
+
+static int secvar_sysfs_load(void)
+{
+	char *name;
+	uint64_t namesize = 0;
+	struct kobject *kobj;
+	int rc;
+
+	name = kzalloc(NAME_MAX_SIZE, GFP_KERNEL);
+	if (!name)
+		return -ENOMEM;
+
+	do {
+		rc = secvar_ops->get_next(name, &namesize, NAME_MAX_SIZE);
+		if (rc) {
+			if (rc != -ENOENT)
+				pr_err("error getting secvar from firmware %d\n",
+				       rc);
+			break;
+		}
+
+		kobj = kzalloc(sizeof(*kobj), GFP_KERNEL);
+		if (!kobj) {
+			rc = -ENOMEM;
+			break;
+		}
+
+		kobject_init(kobj, &secvar_ktype);
+
+		rc = kobject_add(kobj, &secvar_kset->kobj, "%s", name);
+		if (rc) {
+			pr_warn("kobject_add error %d for attribute: %s\n", rc,
+				name);
+			kobject_put(kobj);
+			kobj = NULL;
+		}
+
+		if (kobj)
+			kobject_uevent(kobj, KOBJ_ADD);
+
+	} while (!rc);
+
+	kfree(name);
+	return rc;
+}
+
+static int secvar_sysfs_init(void)
+{
+	int rc;
+
+	if (!secvar_ops) {
+		pr_warn("secvar: failed to retrieve secvar operations.\n");
+		return -ENODEV;
+	}
+
+	secvar_kobj = kobject_create_and_add("secvar", firmware_kobj);
+	if (!secvar_kobj) {
+		pr_err("secvar: Failed to create firmware kobj\n");
+		return -ENOMEM;
+	}
+
+	rc = sysfs_create_file(secvar_kobj, &format_attr.attr);
+	if (rc) {
+		kobject_put(secvar_kobj);
+		return -ENOMEM;
+	}
+
+	secvar_kset = kset_create_and_add("vars", NULL, secvar_kobj);
+	if (!secvar_kset) {
+		pr_err("secvar: sysfs kobject registration failed.\n");
+		kobject_put(secvar_kobj);
+		return -ENOMEM;
+	}
+
+	rc = update_kobj_size();
+	if (rc) {
+		pr_err("Cannot read the size of the attribute\n");
+		return rc;
+	}
+
+	secvar_sysfs_load();
+
+	return 0;
+}
+
+late_initcall(secvar_sysfs_init);