1 files changed, 362 insertions, 0 deletions
diff --git a/drivers/firmware/efi/mokvar-table.c b/drivers/firmware/efi/mokvar-table.c
new file mode 100644
index 000000000..38722d200
--- /dev/null
+++ b/drivers/firmware/efi/mokvar-table.c
@@ -0,0 +1,362 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * mokvar-table.c
+ *
+ * Copyright (c) 2020 Red Hat
+ * Author: Lenny Szubowicz <lszubowi@redhat.com>
+ *
+ * This module contains the kernel support for the Linux EFI Machine
+ * Owner Key (MOK) variable configuration table, which is identified by
+ * the LINUX_EFI_MOK_VARIABLE_TABLE_GUID.
+ *
+ * This EFI configuration table provides a more robust alternative to
+ * EFI volatile variables by which an EFI boot loader can pass the
+ * contents of the Machine Owner Key (MOK) certificate stores to the
+ * kernel during boot. If both the EFI MOK config table and corresponding
+ * EFI MOK variables are present, the table should be considered as
+ * more authoritative.
+ *
+ * This module includes code that validates and maps the EFI MOK table,
+ * if it's presence was detected very early in boot.
+ *
+ * Kernel interface routines are provided to walk through all the
+ * entries in the MOK config table or to search for a specific named
+ * entry.
+ *
+ * The contents of the individual named MOK config table entries are
+ * made available to user space via read-only sysfs binary files under:
+ *
+ * /sys/firmware/efi/mok-variables/
+ *
+ */
+#define pr_fmt(fmt) "mokvar: " fmt
+
+#include <linux/capability.h>
+#include <linux/efi.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+
+#include <asm/early_ioremap.h>
+
+/*
+ * The LINUX_EFI_MOK_VARIABLE_TABLE_GUID config table is a packed
+ * sequence of struct efi_mokvar_table_entry, one for each named
+ * MOK variable. The sequence is terminated by an entry with a
+ * completely NULL name and 0 data size.
+ *
+ * efi_mokvar_table_size is set to the computed size of the
+ * MOK config table by efi_mokvar_table_init(). This will be
+ * non-zero if and only if the table if present and has been
+ * validated by efi_mokvar_table_init().
+ */
+static size_t efi_mokvar_table_size;
+
+/*
+ * efi_mokvar_table_va is the kernel virtual address at which the
+ * EFI MOK config table has been mapped by efi_mokvar_sysfs_init().
+ */
+static struct efi_mokvar_table_entry *efi_mokvar_table_va;
+
+/*
+ * Each /sys/firmware/efi/mok-variables/ sysfs file is represented by
+ * an instance of struct efi_mokvar_sysfs_attr on efi_mokvar_sysfs_list.
+ * bin_attr.private points to the associated EFI MOK config table entry.
+ *
+ * This list is created during boot and then remains unchanged.
+ * So no synchronization is currently required to walk the list.
+ */
+struct efi_mokvar_sysfs_attr {
+	struct bin_attribute bin_attr;
+	struct list_head node;
+};
+
+static LIST_HEAD(efi_mokvar_sysfs_list);
+static struct kobject *mokvar_kobj;
+
+/*
+ * efi_mokvar_table_init() - Early boot validation of EFI MOK config table
+ *
+ * If present, validate and compute the size of the EFI MOK variable
+ * configuration table. This table may be provided by an EFI boot loader
+ * as an alternative to ordinary EFI variables, due to platform-dependent
+ * limitations. The memory occupied by this table is marked as reserved.
+ *
+ * This routine must be called before efi_free_boot_services() in order
+ * to guarantee that it can mark the table as reserved.
+ *
+ * Implicit inputs:
+ * efi.mokvar_table:	Physical address of EFI MOK variable config table
+ *			or special value that indicates no such table.
+ *
+ * Implicit outputs:
+ * efi_mokvar_table_size: Computed size of EFI MOK variable config table.
+ *			The table is considered present and valid if this
+ *			is non-zero.
+ */
+void __init efi_mokvar_table_init(void)
+{
+	efi_memory_desc_t md;
+	void *va = NULL;
+	unsigned long cur_offset = 0;
+	unsigned long offset_limit;
+	unsigned long map_size = 0;
+	unsigned long map_size_needed = 0;
+	unsigned long size;
+	struct efi_mokvar_table_entry *mokvar_entry;
+	int err;
+
+	if (!efi_enabled(EFI_MEMMAP))
+		return;
+
+	if (efi.mokvar_table == EFI_INVALID_TABLE_ADDR)
+		return;
+	/*
+	 * The EFI MOK config table must fit within a single EFI memory
+	 * descriptor range.
+	 */
+	err = efi_mem_desc_lookup(efi.mokvar_table, &md);
+	if (err) {
+		pr_warn("EFI MOKvar config table is not within the EFI memory map\n");
+		return;
+	}
+
+	offset_limit = efi_mem_desc_end(&md) - efi.mokvar_table;
+
+	/*
+	 * Validate the MOK config table. Since there is no table header
+	 * from which we could get the total size of the MOK config table,
+	 * we compute the total size as we validate each variably sized
+	 * entry, remapping as necessary.
+	 */
+	err = -EINVAL;
+	while (cur_offset + sizeof(*mokvar_entry) <= offset_limit) {
+		mokvar_entry = va + cur_offset;
+		map_size_needed = cur_offset + sizeof(*mokvar_entry);
+		if (map_size_needed > map_size) {
+			if (va)
+				early_memunmap(va, map_size);
+			/*
+			 * Map a little more than the fixed size entry
+			 * header, anticipating some data. It's safe to
+			 * do so as long as we stay within current memory
+			 * descriptor.
+			 */
+			map_size = min(map_size_needed + 2*EFI_PAGE_SIZE,
+				       offset_limit);
+			va = early_memremap(efi.mokvar_table, map_size);
+			if (!va) {
+				pr_err("Failed to map EFI MOKvar config table pa=0x%lx, size=%lu.\n",
+				       efi.mokvar_table, map_size);
+				return;
+			}
+			mokvar_entry = va + cur_offset;
+		}
+
+		/* Check for last sentinel entry */
+		if (mokvar_entry->name[0] == '\0') {
+			if (mokvar_entry->data_size != 0)
+				break;
+			err = 0;
+			break;
+		}
+
+		/* Sanity check that the name is null terminated */
+		size = strnlen(mokvar_entry->name,
+			       sizeof(mokvar_entry->name));
+		if (size >= sizeof(mokvar_entry->name))
+			break;
+
+		/* Advance to the next entry */
+		cur_offset = map_size_needed + mokvar_entry->data_size;
+	}
+
+	if (va)
+		early_memunmap(va, map_size);
+	if (err) {
+		pr_err("EFI MOKvar config table is not valid\n");
+		return;
+	}
+
+	if (md.type == EFI_BOOT_SERVICES_DATA)
+		efi_mem_reserve(efi.mokvar_table, map_size_needed);
+
+	efi_mokvar_table_size = map_size_needed;
+}
+
+/*
+ * efi_mokvar_entry_next() - Get next entry in the EFI MOK config table
+ *
+ * mokvar_entry:	Pointer to current EFI MOK config table entry
+ *			or null. Null indicates get first entry.
+ *			Passed by reference. This is updated to the
+ *			same value as the return value.
+ *
+ * Returns:		Pointer to next EFI MOK config table entry
+ *			or null, if there are no more entries.
+ *			Same value is returned in the mokvar_entry
+ *			parameter.
+ *
+ * This routine depends on the EFI MOK config table being entirely
+ * mapped with it's starting virtual address in efi_mokvar_table_va.
+ */
+struct efi_mokvar_table_entry *efi_mokvar_entry_next(
+			struct efi_mokvar_table_entry **mokvar_entry)
+{
+	struct efi_mokvar_table_entry *mokvar_cur;
+	struct efi_mokvar_table_entry *mokvar_next;
+	size_t size_cur;
+
+	mokvar_cur = *mokvar_entry;
+	*mokvar_entry = NULL;
+
+	if (efi_mokvar_table_va == NULL)
+		return NULL;
+
+	if (mokvar_cur == NULL) {
+		mokvar_next = efi_mokvar_table_va;
+	} else {
+		if (mokvar_cur->name[0] == '\0')
+			return NULL;
+		size_cur = sizeof(*mokvar_cur) + mokvar_cur->data_size;
+		mokvar_next = (void *)mokvar_cur + size_cur;
+	}
+
+	if (mokvar_next->name[0] == '\0')
+		return NULL;
+
+	*mokvar_entry = mokvar_next;
+	return mokvar_next;
+}
+
+/*
+ * efi_mokvar_entry_find() - Find EFI MOK config entry by name
+ *
+ * name:	Name of the entry to look for.
+ *
+ * Returns:	Pointer to EFI MOK config table entry if found;
+ *		null otherwise.
+ *
+ * This routine depends on the EFI MOK config table being entirely
+ * mapped with it's starting virtual address in efi_mokvar_table_va.
+ */
+struct efi_mokvar_table_entry *efi_mokvar_entry_find(const char *name)
+{
+	struct efi_mokvar_table_entry *mokvar_entry = NULL;
+
+	while (efi_mokvar_entry_next(&mokvar_entry)) {
+		if (!strncmp(name, mokvar_entry->name,
+			     sizeof(mokvar_entry->name)))
+			return mokvar_entry;
+	}
+	return NULL;
+}
+
+/*
+ * efi_mokvar_sysfs_read() - sysfs binary file read routine
+ *
+ * Returns:	Count of bytes read.
+ *
+ * Copy EFI MOK config table entry data for this mokvar sysfs binary file
+ * to the supplied buffer, starting at the specified offset into mokvar table
+ * entry data, for the specified count bytes. The copy is limited by the
+ * amount of data in this mokvar config table entry.
+ */
+static ssize_t efi_mokvar_sysfs_read(struct file *file, struct kobject *kobj,
+				 struct bin_attribute *bin_attr, char *buf,
+				 loff_t off, size_t count)
+{
+	struct efi_mokvar_table_entry *mokvar_entry = bin_attr->private;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return 0;
+
+	if (off >= mokvar_entry->data_size)
+		return 0;
+	if (count >  mokvar_entry->data_size - off)
+		count = mokvar_entry->data_size - off;
+
+	memcpy(buf, mokvar_entry->data + off, count);
+	return count;
+}
+
+/*
+ * efi_mokvar_sysfs_init() - Map EFI MOK config table and create sysfs
+ *
+ * Map the EFI MOK variable config table for run-time use by the kernel
+ * and create the sysfs entries in /sys/firmware/efi/mok-variables/
+ *
+ * This routine just returns if a valid EFI MOK variable config table
+ * was not found earlier during boot.
+ *
+ * This routine must be called during a "middle" initcall phase, i.e.
+ * after efi_mokvar_table_init() but before UEFI certs are loaded
+ * during late init.
+ *
+ * Implicit inputs:
+ * efi.mokvar_table:	Physical address of EFI MOK variable config table
+ *			or special value that indicates no such table.
+ *
+ * efi_mokvar_table_size: Computed size of EFI MOK variable config table.
+ *			The table is considered present and valid if this
+ *			is non-zero.
+ *
+ * Implicit outputs:
+ * efi_mokvar_table_va:	Start virtual address of the EFI MOK config table.
+ */
+static int __init efi_mokvar_sysfs_init(void)
+{
+	void *config_va;
+	struct efi_mokvar_table_entry *mokvar_entry = NULL;
+	struct efi_mokvar_sysfs_attr *mokvar_sysfs = NULL;
+	int err = 0;
+
+	if (efi_mokvar_table_size == 0)
+		return -ENOENT;
+
+	config_va = memremap(efi.mokvar_table, efi_mokvar_table_size,
+			     MEMREMAP_WB);
+	if (!config_va) {
+		pr_err("Failed to map EFI MOKvar config table\n");
+		return -ENOMEM;
+	}
+	efi_mokvar_table_va = config_va;
+
+	mokvar_kobj = kobject_create_and_add("mok-variables", efi_kobj);
+	if (!mokvar_kobj) {
+		pr_err("Failed to create EFI mok-variables sysfs entry\n");
+		return -ENOMEM;
+	}
+
+	while (efi_mokvar_entry_next(&mokvar_entry)) {
+		mokvar_sysfs = kzalloc(sizeof(*mokvar_sysfs), GFP_KERNEL);
+		if (!mokvar_sysfs) {
+			err = -ENOMEM;
+			break;
+		}
+
+		sysfs_bin_attr_init(&mokvar_sysfs->bin_attr);
+		mokvar_sysfs->bin_attr.private = mokvar_entry;
+		mokvar_sysfs->bin_attr.attr.name = mokvar_entry->name;
+		mokvar_sysfs->bin_attr.attr.mode = 0400;
+		mokvar_sysfs->bin_attr.size = mokvar_entry->data_size;
+		mokvar_sysfs->bin_attr.read = efi_mokvar_sysfs_read;
+
+		err = sysfs_create_bin_file(mokvar_kobj,
+					   &mokvar_sysfs->bin_attr);
+		if (err)
+			break;
+
+		list_add_tail(&mokvar_sysfs->node, &efi_mokvar_sysfs_list);
+	}
+
+	if (err) {
+		pr_err("Failed to create some EFI mok-variables sysfs entries\n");
+		kfree(mokvar_sysfs);
+	}
+	return err;
+}
+device_initcall(efi_mokvar_sysfs_init);