1 files changed, 349 insertions, 0 deletions
diff --git a/drivers/virt/coco/efi_secret/efi_secret.c b/drivers/virt/coco/efi_secret/efi_secret.c
new file mode 100644
index 000000000..e700a5ef7
--- /dev/null
+++ b/drivers/virt/coco/efi_secret/efi_secret.c
@@ -0,0 +1,349 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * efi_secret module
+ *
+ * Copyright (C) 2022 IBM Corporation
+ * Author: Dov Murik <dovmurik@linux.ibm.com>
+ */
+
+/**
+ * DOC: efi_secret: Allow reading EFI confidential computing (coco) secret area
+ * via securityfs interface.
+ *
+ * When the module is loaded (and securityfs is mounted, typically under
+ * /sys/kernel/security), a "secrets/coco" directory is created in securityfs.
+ * In it, a file is created for each secret entry.  The name of each such file
+ * is the GUID of the secret entry, and its content is the secret data.
+ */
+
+#include <linux/platform_device.h>
+#include <linux/seq_file.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/io.h>
+#include <linux/security.h>
+#include <linux/efi.h>
+#include <linux/cacheflush.h>
+
+#define EFI_SECRET_NUM_FILES 64
+
+struct efi_secret {
+	struct dentry *secrets_dir;
+	struct dentry *fs_dir;
+	struct dentry *fs_files[EFI_SECRET_NUM_FILES];
+	void __iomem *secret_data;
+	u64 secret_data_len;
+};
+
+/*
+ * Structure of the EFI secret area
+ *
+ * Offset   Length
+ * (bytes)  (bytes)  Usage
+ * -------  -------  -----
+ *       0       16  Secret table header GUID (must be 1e74f542-71dd-4d66-963e-ef4287ff173b)
+ *      16        4  Length of bytes of the entire secret area
+ *
+ *      20       16  First secret entry's GUID
+ *      36        4  First secret entry's length in bytes (= 16 + 4 + x)
+ *      40        x  First secret entry's data
+ *
+ *    40+x       16  Second secret entry's GUID
+ *    56+x        4  Second secret entry's length in bytes (= 16 + 4 + y)
+ *    60+x        y  Second secret entry's data
+ *
+ * (... and so on for additional entries)
+ *
+ * The GUID of each secret entry designates the usage of the secret data.
+ */
+
+/**
+ * struct secret_header - Header of entire secret area; this should be followed
+ * by instances of struct secret_entry.
+ * @guid:	Must be EFI_SECRET_TABLE_HEADER_GUID
+ * @len:	Length in bytes of entire secret area, including header
+ */
+struct secret_header {
+	efi_guid_t guid;
+	u32 len;
+} __attribute((packed));
+
+/**
+ * struct secret_entry - Holds one secret entry
+ * @guid:	Secret-specific GUID (or NULL_GUID if this secret entry was deleted)
+ * @len:	Length of secret entry, including its guid and len fields
+ * @data:	The secret data (full of zeros if this secret entry was deleted)
+ */
+struct secret_entry {
+	efi_guid_t guid;
+	u32 len;
+	u8 data[];
+} __attribute((packed));
+
+static size_t secret_entry_data_len(struct secret_entry *e)
+{
+	return e->len - sizeof(*e);
+}
+
+static struct efi_secret the_efi_secret;
+
+static inline struct efi_secret *efi_secret_get(void)
+{
+	return &the_efi_secret;
+}
+
+static int efi_secret_bin_file_show(struct seq_file *file, void *data)
+{
+	struct secret_entry *e = file->private;
+
+	if (e)
+		seq_write(file, e->data, secret_entry_data_len(e));
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(efi_secret_bin_file);
+
+/*
+ * Overwrite memory content with zeroes, and ensure that dirty cache lines are
+ * actually written back to memory, to clear out the secret.
+ */
+static void wipe_memory(void *addr, size_t size)
+{
+	memzero_explicit(addr, size);
+#ifdef CONFIG_X86
+	clflush_cache_range(addr, size);
+#endif
+}
+
+static int efi_secret_unlink(struct inode *dir, struct dentry *dentry)
+{
+	struct efi_secret *s = efi_secret_get();
+	struct inode *inode = d_inode(dentry);
+	struct secret_entry *e = (struct secret_entry *)inode->i_private;
+	int i;
+
+	if (e) {
+		/* Zero out the secret data */
+		wipe_memory(e->data, secret_entry_data_len(e));
+		e->guid = NULL_GUID;
+	}
+
+	inode->i_private = NULL;
+
+	for (i = 0; i < EFI_SECRET_NUM_FILES; i++)
+		if (s->fs_files[i] == dentry)
+			s->fs_files[i] = NULL;
+
+	/*
+	 * securityfs_remove tries to lock the directory's inode, but we reach
+	 * the unlink callback when it's already locked
+	 */
+	inode_unlock(dir);
+	securityfs_remove(dentry);
+	inode_lock(dir);
+
+	return 0;
+}
+
+static const struct inode_operations efi_secret_dir_inode_operations = {
+	.lookup         = simple_lookup,
+	.unlink         = efi_secret_unlink,
+};
+
+static int efi_secret_map_area(struct platform_device *dev)
+{
+	int ret;
+	struct efi_secret *s = efi_secret_get();
+	struct linux_efi_coco_secret_area *secret_area;
+
+	if (efi.coco_secret == EFI_INVALID_TABLE_ADDR) {
+		dev_err(&dev->dev, "Secret area address is not available\n");
+		return -EINVAL;
+	}
+
+	secret_area = memremap(efi.coco_secret, sizeof(*secret_area), MEMREMAP_WB);
+	if (secret_area == NULL) {
+		dev_err(&dev->dev, "Could not map secret area EFI config entry\n");
+		return -ENOMEM;
+	}
+	if (!secret_area->base_pa || secret_area->size < sizeof(struct secret_header)) {
+		dev_err(&dev->dev,
+			"Invalid secret area memory location (base_pa=0x%llx size=0x%llx)\n",
+			secret_area->base_pa, secret_area->size);
+		ret = -EINVAL;
+		goto unmap;
+	}
+
+	s->secret_data = ioremap_encrypted(secret_area->base_pa, secret_area->size);
+	if (s->secret_data == NULL) {
+		dev_err(&dev->dev, "Could not map secret area\n");
+		ret = -ENOMEM;
+		goto unmap;
+	}
+
+	s->secret_data_len = secret_area->size;
+	ret = 0;
+
+unmap:
+	memunmap(secret_area);
+	return ret;
+}
+
+static void efi_secret_securityfs_teardown(struct platform_device *dev)
+{
+	struct efi_secret *s = efi_secret_get();
+	int i;
+
+	for (i = (EFI_SECRET_NUM_FILES - 1); i >= 0; i--) {
+		securityfs_remove(s->fs_files[i]);
+		s->fs_files[i] = NULL;
+	}
+
+	securityfs_remove(s->fs_dir);
+	s->fs_dir = NULL;
+
+	securityfs_remove(s->secrets_dir);
+	s->secrets_dir = NULL;
+
+	dev_dbg(&dev->dev, "Removed securityfs entries\n");
+}
+
+static int efi_secret_securityfs_setup(struct platform_device *dev)
+{
+	struct efi_secret *s = efi_secret_get();
+	int ret = 0, i = 0, bytes_left;
+	unsigned char *ptr;
+	struct secret_header *h;
+	struct secret_entry *e;
+	struct dentry *dent;
+	char guid_str[EFI_VARIABLE_GUID_LEN + 1];
+
+	ptr = (void __force *)s->secret_data;
+	h = (struct secret_header *)ptr;
+	if (efi_guidcmp(h->guid, EFI_SECRET_TABLE_HEADER_GUID)) {
+		/*
+		 * This is not an error: it just means that EFI defines secret
+		 * area but it was not populated by the Guest Owner.
+		 */
+		dev_dbg(&dev->dev, "EFI secret area does not start with correct GUID\n");
+		return -ENODEV;
+	}
+	if (h->len < sizeof(*h)) {
+		dev_err(&dev->dev, "EFI secret area reported length is too small\n");
+		return -EINVAL;
+	}
+	if (h->len > s->secret_data_len) {
+		dev_err(&dev->dev, "EFI secret area reported length is too big\n");
+		return -EINVAL;
+	}
+
+	s->secrets_dir = NULL;
+	s->fs_dir = NULL;
+	memset(s->fs_files, 0, sizeof(s->fs_files));
+
+	dent = securityfs_create_dir("secrets", NULL);
+	if (IS_ERR(dent)) {
+		dev_err(&dev->dev, "Error creating secrets securityfs directory entry err=%ld\n",
+			PTR_ERR(dent));
+		return PTR_ERR(dent);
+	}
+	s->secrets_dir = dent;
+
+	dent = securityfs_create_dir("coco", s->secrets_dir);
+	if (IS_ERR(dent)) {
+		dev_err(&dev->dev, "Error creating coco securityfs directory entry err=%ld\n",
+			PTR_ERR(dent));
+		return PTR_ERR(dent);
+	}
+	d_inode(dent)->i_op = &efi_secret_dir_inode_operations;
+	s->fs_dir = dent;
+
+	bytes_left = h->len - sizeof(*h);
+	ptr += sizeof(*h);
+	while (bytes_left >= (int)sizeof(*e) && i < EFI_SECRET_NUM_FILES) {
+		e = (struct secret_entry *)ptr;
+		if (e->len < sizeof(*e) || e->len > (unsigned int)bytes_left) {
+			dev_err(&dev->dev, "EFI secret area is corrupted\n");
+			ret = -EINVAL;
+			goto err_cleanup;
+		}
+
+		/* Skip deleted entries (which will have NULL_GUID) */
+		if (efi_guidcmp(e->guid, NULL_GUID)) {
+			efi_guid_to_str(&e->guid, guid_str);
+
+			dent = securityfs_create_file(guid_str, 0440, s->fs_dir, (void *)e,
+						      &efi_secret_bin_file_fops);
+			if (IS_ERR(dent)) {
+				dev_err(&dev->dev, "Error creating efi_secret securityfs entry\n");
+				ret = PTR_ERR(dent);
+				goto err_cleanup;
+			}
+
+			s->fs_files[i++] = dent;
+		}
+		ptr += e->len;
+		bytes_left -= e->len;
+	}
+
+	dev_info(&dev->dev, "Created %d entries in securityfs secrets/coco\n", i);
+	return 0;
+
+err_cleanup:
+	efi_secret_securityfs_teardown(dev);
+	return ret;
+}
+
+static void efi_secret_unmap_area(void)
+{
+	struct efi_secret *s = efi_secret_get();
+
+	if (s->secret_data) {
+		iounmap(s->secret_data);
+		s->secret_data = NULL;
+		s->secret_data_len = 0;
+	}
+}
+
+static int efi_secret_probe(struct platform_device *dev)
+{
+	int ret;
+
+	ret = efi_secret_map_area(dev);
+	if (ret)
+		return ret;
+
+	ret = efi_secret_securityfs_setup(dev);
+	if (ret)
+		goto err_unmap;
+
+	return ret;
+
+err_unmap:
+	efi_secret_unmap_area();
+	return ret;
+}
+
+static int efi_secret_remove(struct platform_device *dev)
+{
+	efi_secret_securityfs_teardown(dev);
+	efi_secret_unmap_area();
+	return 0;
+}
+
+static struct platform_driver efi_secret_driver = {
+	.probe = efi_secret_probe,
+	.remove = efi_secret_remove,
+	.driver = {
+		.name = "efi_secret",
+	},
+};
+
+module_platform_driver(efi_secret_driver);
+
+MODULE_DESCRIPTION("Confidential computing EFI secret area access");
+MODULE_AUTHOR("IBM");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:efi_secret");