[PATCH 5/9] virt: efi_secret: Transition to the faux device interface

Sudeep Holla
2025-03-17T10:13:58Z

The EFI secret area driver does not require the creation of a platform
device. Originally, this approach was chosen for simplicity when the
driver was first implemented.

With the introduction of the lightweight faux device interface, we now
have a more appropriate alternative. Migrate the driver to utilize the
faux bus, given that the platform device it previously created was not
a real one anyway. This will simplify the code, reducing its footprint
while maintaining functionality.

Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: linux-efi@vger.kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
---
drivers/firmware/efi/efi.c | 6 -----
drivers/virt/coco/efi_secret/efi_secret.c | 41 ++++++++++++++++++-------------
2 files changed, 24 insertions(+), 23 deletions(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 18deb2d212ce6944927f5e3a9a40bb6754e7ffa9..4654a88d4e12f354a891118edf9001755285c69a 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -24,7 +24,6 @@
#include <linux/initrd.h>
#include <linux/io.h>
#include <linux/kexec.h>
-#include <linux/platform_device.h>
#include <linux/random.h>
#include <linux/reboot.h>
#include <linux/slab.h>
@@ -464,11 +463,6 @@ static int __init efisubsys_init(void)
if (efi_enabled(EFI_DBG) && efi_enabled(EFI_PRESERVE_BS_REGIONS))
efi_debugfs_init();

-#ifdef CONFIG_EFI_COCO_SECRET
- if (efi.coco_secret != EFI_INVALID_TABLE_ADDR)
- platform_device_register_simple("efi_secret", 0, NULL, 0);
-#endif
-
return 0;

err_remove_group:
diff --git a/drivers/virt/coco/efi_secret/efi_secret.c b/drivers/virt/coco/efi_secret/efi_secret.c
index 1864f9f80617e082feb574a15327949972c8cc1e..4ba1a9f3b8a90981795d296d0a8dfdc9edb22966 100644
--- a/drivers/virt/coco/efi_secret/efi_secret.c
+++ b/drivers/virt/coco/efi_secret/efi_secret.c
@@ -16,7 +16,7 @@
* is the GUID of the secret entry, and its content is the secret data.
*/

-#include <linux/platform_device.h>
+#include <linux/device/faux.h>
#include <linux/seq_file.h>
#include <linux/fs.h>
#include <linux/kernel.h>
@@ -152,17 +152,12 @@ static const struct inode_operations efi_secret_dir_inode_operations = {
.unlink = efi_secret_unlink,
};

-static int efi_secret_map_area(struct platform_device *dev)
+static int efi_secret_map_area(struct faux_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");
@@ -191,7 +186,7 @@ static int efi_secret_map_area(struct platform_device *dev)
return ret;
}

-static void efi_secret_securityfs_teardown(struct platform_device *dev)
+static void efi_secret_securityfs_teardown(struct faux_device *dev)
{
struct efi_secret *s = efi_secret_get();
int i;
@@ -210,7 +205,7 @@ static void efi_secret_securityfs_teardown(struct platform_device *dev)
dev_dbg(&dev->dev, "Removed securityfs entries\n");
}

-static int efi_secret_securityfs_setup(struct platform_device *dev)
+static int efi_secret_securityfs_setup(struct faux_device *dev)
{
struct efi_secret *s = efi_secret_get();
int ret = 0, i = 0, bytes_left;
@@ -307,7 +302,7 @@ static void efi_secret_unmap_area(void)
}
}

-static int efi_secret_probe(struct platform_device *dev)
+static int efi_secret_probe(struct faux_device *dev)
{
int ret;

@@ -326,23 +321,35 @@ static int efi_secret_probe(struct platform_device *dev)
return ret;
}

-static void efi_secret_remove(struct platform_device *dev)
+static void efi_secret_remove(struct faux_device *dev)
{
efi_secret_securityfs_teardown(dev);
efi_secret_unmap_area();
}

-static struct platform_driver efi_secret_driver = {
+static struct faux_device_ops efi_secret_ops = {
.probe = efi_secret_probe,
.remove = efi_secret_remove,
- .driver = {
- .name = "efi_secret",
- },
};

-module_platform_driver(efi_secret_driver);
+static int __init efi_secret_init(void)
+{
+ struct faux_device *fdev;
+
+ if (efi.coco_secret == EFI_INVALID_TABLE_ADDR)
+ return 0;
+
+ fdev = faux_device_create("efi_secret", NULL, &efi_secret_ops);
+ if (!fdev) {
+ pr_err("efi_secret: could not create the device\n");
+ return -ENODEV;
+ }
+
+ return 0;
+}
+device_initcall(efi_secret_init);

MODULE_DESCRIPTION("Confidential computing EFI secret area access");
MODULE_AUTHOR("IBM");
MODULE_LICENSE("GPL");
-MODULE_ALIAS("platform:efi_secret");
+MODULE_ALIAS("faux:efi_secret");

--
2.34.1