Re: [PATCH v8 3/4] efi: Load efi_secret module if EFI secret area is populated

Ard Biesheuvel
2022-02-28T12:49:37Z

On Mon, 28 Feb 2022 at 12:43, Dov Murik <dovmurik@linux.ibm.com> wrote:
>
> If the efi_secret module is built, register a late_initcall in the EFI
> driver which checks whether the EFI secret area is available and
> populated, and then requests to load the efi_secret module.
>
> This will cause the <securityfs>/secrets/coco directory to appear in
> guests into which secrets were injected; in other cases, the module is
> not loaded.
>
> Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
> Reviewed-by: Gerd Hoffmann <kraxel@redhat.com>

It would be better to simply expose a platform device and associated
driver, instead of hooking into the module machinery directly.

We already do something similar for the EFI rtc and the efivars
subsystem, using platform_device_register_simple()

> ---
> drivers/firmware/efi/Makefile | 1 +
> drivers/firmware/efi/coco.c | 58 ++++++++++++++++++++
> drivers/virt/coco/efi_secret/Kconfig | 3 +
> 3 files changed, 62 insertions(+)
>
> diff --git a/drivers/firmware/efi/Makefile b/drivers/firmware/efi/Makefile
> index c02ff25dd477..49c4a8c0bfc4 100644
> --- a/drivers/firmware/efi/Makefile
> +++ b/drivers/firmware/efi/Makefile
> @@ -32,6 +32,7 @@ obj-$(CONFIG_APPLE_PROPERTIES) += apple-properties.o
> obj-$(CONFIG_EFI_RCI2_TABLE) += rci2-table.o
> obj-$(CONFIG_EFI_EMBEDDED_FIRMWARE) += embedded-firmware.o
> obj-$(CONFIG_LOAD_UEFI_KEYS) += mokvar-table.o
> +obj-$(CONFIG_EFI_COCO_SECRET) += coco.o
>
> fake_map-y += fake_mem.o
> fake_map-$(CONFIG_X86) += x86_fake_mem.o
> diff --git a/drivers/firmware/efi/coco.c b/drivers/firmware/efi/coco.c
> new file mode 100644
> index 000000000000..f8efd240ab05
> --- /dev/null
> +++ b/drivers/firmware/efi/coco.c
> @@ -0,0 +1,58 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Confidential computing (coco) secret area handling
> + *
> + * Copyright (C) 2021 IBM Corporation
> + * Author: Dov Murik <dovmurik@linux.ibm.com>
> + */
> +
> +#define pr_fmt(fmt) "efi: " fmt
> +
> +#include <linux/efi.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kmod.h>
> +
> +#ifdef CONFIG_EFI_SECRET_MODULE
> +
> +/*
> + * Load the efi_secret module if the EFI secret area is populated
> + */
> +static int __init load_efi_secret_module(void)
> +{
> + struct linux_efi_coco_secret_area *area;
> + efi_guid_t *header_guid;
> + int ret = 0;
> +
> + if (efi.coco_secret == EFI_INVALID_TABLE_ADDR)
> + return 0;
> +
> + area = memremap(efi.coco_secret, sizeof(*area), MEMREMAP_WB);
> + if (!area) {
> + pr_err("Failed to map confidential computing secret area descriptor\n");
> + return -ENOMEM;
> + }
> + if (!area->base_pa || area->size < sizeof(*header_guid))
> + goto unmap_desc;
> +
> + header_guid = (void __force *)ioremap_encrypted(area->base_pa, sizeof(*header_guid));
> + if (!header_guid) {
> + pr_err("Failed to map secret area\n");
> + ret = -ENOMEM;
> + goto unmap_desc;
> + }
> + if (efi_guidcmp(*header_guid, EFI_SECRET_TABLE_HEADER_GUID))
> + goto unmap_encrypted;
> +
> + ret = request_module("efi_secret");
> +
> +unmap_encrypted:
> + iounmap((void __iomem *)header_guid);
> +
> +unmap_desc:
> + memunmap(area);
> + return ret;
> +}
> +late_initcall(load_efi_secret_module);
> +
> +#endif
> diff --git a/drivers/virt/coco/efi_secret/Kconfig b/drivers/virt/coco/efi_secret/Kconfig
> index 4404d198f3b2..dc8da2921e36 100644
> --- a/drivers/virt/coco/efi_secret/Kconfig
> +++ b/drivers/virt/coco/efi_secret/Kconfig
> @@ -14,3 +14,6 @@ config EFI_SECRET
>
> To compile this driver as a module, choose M here.
> The module will be called efi_secret.
> +
> + The module is loaded automatically by the EFI driver if the EFI
> + secret area is populated.
> --
> 2.25.1
>