linux-kernel - Re: [PATCH v2 5/8] virt: efi_secret: Transition to the faux device interface

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Message-ID: <CAMj1kXGJkApH73r9qEGABe3M4pXP2gMW3tDXfz2F6WGPZ3nhug@mail.gmail.com>
Date: Tue, 18 Mar 2025 18:10:41 +0100
From: Ard Biesheuvel <ardb@...nel.org>
To: Sudeep Holla <sudeep.holla@....com>
Cc: linux-kernel@...r.kernel.org, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, linux-efi@...r.kernel.org
Subject: Re: [PATCH v2 5/8] virt: efi_secret: Transition to the faux device interface

On Tue, 18 Mar 2025 at 18:02, Sudeep Holla <sudeep.holla@....com> wrote:
>
> 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@...nel.org>
> Cc: linux-efi@...r.kernel.org
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>

So how is module autoload supposed to work with this driver?


> ---
>  drivers/firmware/efi/efi.c                |  5 -----
>  drivers/virt/coco/efi_secret/efi_secret.c | 29 ++++++++---------------------
>  2 files changed, 8 insertions(+), 26 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 8aebc747c65bc1b63d514a50fe6f35a9e3c1af0a..862b7744c28ecc9e5a64bbb3533c34119f50267f 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -465,11 +465,6 @@ 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..a60976750bef787c78401bf4569ee5d0c7d2b5f4 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 +321,15 @@ 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 = {
> -       .probe = efi_secret_probe,
> -       .remove = efi_secret_remove,
> -       .driver = {
> -               .name = "efi_secret",
> -       },
> -};
> -
> -module_platform_driver(efi_secret_driver);
> +module_faux_driver(efi_secret, efi_secret_probe, efi_secret_remove,
> +                  efi.coco_secret != EFI_INVALID_TABLE_ADDR);
>
>  MODULE_DESCRIPTION("Confidential computing EFI secret area access");
>  MODULE_AUTHOR("IBM");
>  MODULE_LICENSE("GPL");
> -MODULE_ALIAS("platform:efi_secret");
>
> --
> 2.34.1
>