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

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Message-ID: <CAMj1kXFybkGtxH2U6oAi_Qeqe-i_kH-hZjUZKY3-UzPHUg55vg@mail.gmail.com>
Date:   Mon, 28 Feb 2022 13:49:19 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Dov Murik <dovmurik@...ux.ibm.com>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Gerd Hoffmann <kraxel@...hat.com>,
        Borislav Petkov <bp@...e.de>,
        Ashish Kalra <ashish.kalra@....com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrew Scull <ascull@...gle.com>,
        Dave Hansen <dave.hansen@...el.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Lenny Szubowicz <lszubowi@...hat.com>,
        Peter Gonda <pgonda@...gle.com>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        James Bottomley <jejb@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@...ux.ibm.com>,
        Jim Cadden <jcadden@....com>,
        Daniele Buono <dbuono@...ux.vnet.ibm.com>,
        linux-coco@...ts.linux.dev, linux-security-module@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 3/4] efi: Load efi_secret module if EFI secret area is populated

On Mon, 28 Feb 2022 at 12:43, Dov Murik <dovmurik@...ux.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@...ux.ibm.com>
> Reviewed-by: Gerd Hoffmann <kraxel@...hat.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@...ux.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
>