linux-kernel - Re: [PATCH v8 1/4] efi: Introduce EFI_FIRMWARE_MANAGEMENT_CAPSULE

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Date:   Thu, 18 Nov 2021 16:49:35 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>, Len Brown <lenb@...nel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...el.com>,
        Mike Rapoport <rppt@...nel.org>,
        Aubrey Li <aubrey.li@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 1/4] efi: Introduce EFI_FIRMWARE_MANAGEMENT_CAPSULE_HEADER
 and corresponding structures

On Wed, Nov 3, 2021 at 4:44 PM Chen Yu <yu.c.chen@...el.com> wrote:
>
> Platform Firmware Runtime Update image starts with UEFI headers, and the
> headers are defined in UEFI specification, but some of them have not been
> defined in the kernel yet.
>
> For example, the header layout of a capsule file looks like this:
>
> EFI_CAPSULE_HEADER
> EFI_FIRMWARE_MANAGEMENT_CAPSULE_HEADER
> EFI_FIRMWARE_MANAGEMENT_CAPSULE_IMAGE_HEADER
> EFI_FIRMWARE_IMAGE_AUTHENTICATION
>
> These structures would be used by the Platform Firmware Runtime Update
> driver to parse the format of capsule file to verify if the corresponding
> version number is valid.

Why does the driver need to do that?

The firmware will reject the update if the version is invalid anyway, won't it?

> The EFI_CAPSULE_HEADER has been defined in the
> kernel, however the rest are not, thus introduce corresponding UEFI
> structures accordingly.

I would change the above in the following way:

"EFI_CAPSULE_HEADER has been defined in the kernel, but the other
structures have not been defined yet, so do that."

> Besides, EFI_FIRMWARE_MANAGEMENT_CAPSULE_HEADER
> and EFI_FIRMWARE_MANAGEMENT_CAPSULE_IMAGE_HEADER are required to be packed
> in the uefi specification.

> Ard has pointed out that, the __packed
> attribute does indicate to the compiler that the entire thing can appear
> misaligned in memory. So if one follows the other in the capsule header,
> the __packed attribute may be appropriate to ensure that the second one
> is not accessed using misaligned loads and stores.

"For this reason, use the __packed attribute to indicate to the
compiler that the entire structure can appear misaligned in memory (as
suggested by Ard) in case one of them follows the other directly in a
capsule header."

>
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
> v8: Use efi_guid_t instead of guid_t. (Andy Shevchenko)
> v7: Use __packed instead of pragma pack(1). (Greg Kroah-Hartman, Ard Biesheuve)
> v6: No change since v5.
> v5: No change since v4.
> v4: Revise the commit log to make it more clear. (Rafael J. Wysocki)
> ---
>  include/linux/efi.h | 46 +++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 46 insertions(+)
>
> diff --git a/include/linux/efi.h b/include/linux/efi.h
> index 6b5d36babfcc..1ec73c5ab6c9 100644
> --- a/include/linux/efi.h
> +++ b/include/linux/efi.h
> @@ -148,6 +148,52 @@ typedef struct {
>         u32 imagesize;
>  } efi_capsule_header_t;
>
> +/* EFI_FIRMWARE_MANAGEMENT_CAPSULE_HEADER */
> +struct efi_manage_capsule_header {
> +       u32 ver;
> +       u16 emb_drv_cnt;
> +       u16 payload_cnt;
> +       /*
> +        * Variable array indicated by number of
> +        * (emb_drv_cnt + payload_cnt)

* Variable-size array of the size given by the sum of
* emb_drv_cnt and payload_cnt.

> +        */
> +       u64 offset_list[];
> +} __packed;
> +
> +/* EFI_FIRMWARE_MANAGEMENT_CAPSULE_IMAGE_HEADER */
> +struct efi_manage_capsule_image_header {
> +       u32 ver;
> +       efi_guid_t image_type_id;
> +       u8 image_index;
> +       u8 reserved_bytes[3];
> +       u32 image_size;
> +       u32 vendor_code_size;
> +       /* ver = 2. */

What does this mean?

> +       u64 hw_ins;
> +       /* ver = v3. */

And same here?

> +       u64 capsule_support;
> +} __packed;
> +
> +/* WIN_CERTIFICATE */
> +struct win_cert {
> +       u32 len;
> +       u16 rev;
> +       u16 cert_type;
> +};
> +
> +/* WIN_CERTIFICATE_UEFI_GUID */
> +struct win_cert_uefi_guid {
> +       struct win_cert hdr;
> +       efi_guid_t cert_type;
> +       u8 cert_data[];
> +};
> +
> +/* EFI_FIRMWARE_IMAGE_AUTHENTICATIO */

The "N" character at the end is missing.

> +struct efi_image_auth {
> +       u64 mon_count;
> +       struct win_cert_uefi_guid auth_info;
> +};
> +
>  /*
>   * EFI capsule flags
>   */
> --