[PATCH 1/2] efi_firmware: set EFI capsule dfu_alt_info env explicitly

[Ilias Apalodimas]

Hi Jonathan,

On Mon, 3 Feb 2025 at 23:54, Jonathan Humphreys <j-humphreys at ti.com> wrote:
>
> The current implementation of EFI capsule update uses set_dfu_alt_info() to
> set the dfu_alt_info environment variable with the settings it requires.
> However, set_dfu_alt_info() is doing this for all DFU operations, even
> those unrelated to capsule update.
>
> Thus other uses of DFU, such as DFU boot which sets its own value for the
> dfu_alt_info environment variable, will have that setting overwritten with
> the capsule update setting. Similarly, any user defined value for the
> dfu_alt_info environment variable would get overwritten when any DFU
> operation was performed, including simply performing a "dfu 0 list"
> command.
>
> The solution is stop using the set_dfu_alt_info() mechanism to set the
> dfu_alt_info environment variable and instead explicitly set it to the
> capsule update's setting just before performing the capsule update's DFU
> operation, and then restore the environment variable back to its original
> value.
>
> This patch implements the explicit setting and restoring of the
> dfu_alt_info environment variable as part of the EFI capsule update
> operation.
>
> The fix is fully implemented in a subsequent patch that removes the capsule
> update dfu_alt_info support in set_dfu_alt_info().
>
> Signed-off-by: Jonathan Humphreys <j-humphreys at ti.com>
> ---
>  lib/efi_loader/efi_firmware.c | 29 +++++++++++++++++++++++++++++
>  1 file changed, 29 insertions(+)
>
> diff --git a/lib/efi_loader/efi_firmware.c b/lib/efi_loader/efi_firmware.c
> index 5a754c9cd03..d8b6d34ccab 100644
> --- a/lib/efi_loader/efi_firmware.c
> +++ b/lib/efi_loader/efi_firmware.c
> @@ -649,8 +649,10 @@ efi_status_t EFIAPI efi_firmware_fit_set_image(
>         efi_status_t (*progress)(efi_uintn_t completion),
>         u16 **abort_reason)
>  {
> +       int ret;
>         efi_status_t status;
>         struct fmp_state state = { 0 };
> +       char *orig_dfu_env;
>
>         EFI_ENTRY("%p %d %p %zu %p %p %p\n", this, image_index, image,
>                   image_size, vendor_code, progress, abort_reason);
> @@ -663,9 +665,22 @@ efi_status_t EFIAPI efi_firmware_fit_set_image(
>         if (status != EFI_SUCCESS)
>                 return EFI_EXIT(status);
>
> +       orig_dfu_env = env_get("dfu_alt_info");

I don't think this will work. env_get returns a pointer to the data
which is going to change after the env_set
IOW this piece

        env_set("dfu_alt_info", "test1");
        orig_dfu_env = env_get("dfu_alt_info");
        printf("now %s\n", orig_dfu_env); -> will print test1

        env_set("dfu_alt_info", "test2");
        dfu_env = env_get("dfu_alt_info");
        printf("Orig %s now %s\n", orig_dfu_env, lala); -> will print
test2 test2

You have to copy the value of the pointer to an allocated piece of
memory to restore it

Thanks
/Ilias


> +       ret = env_set("dfu_alt_info", update_info.dfu_string);
> +       if (ret) {
> +               pr_err("unable to set env variable \"dfu_alt_info\"!\n");
> +               return -EINVAL;
> +       }
> +
>         if (fit_update(image))
>                 return EFI_EXIT(EFI_DEVICE_ERROR);
>
> +       ret = env_set("dfu_alt_info", orig_dfu_env);
> +       if (ret) {
> +               pr_err("unable to set env variable \"dfu_alt_info\"!\n");
> +               return -EINVAL;
> +       }
> +
>         efi_firmware_set_fmp_state_var(&state, image_index);
>
>         return EFI_EXIT(EFI_SUCCESS);
> @@ -717,6 +732,7 @@ efi_status_t EFIAPI efi_firmware_raw_set_image(
>         u8 dfu_alt_num;
>         efi_status_t status;
>         struct fmp_state state = { 0 };
> +       char *orig_dfu_env;
>
>         EFI_ENTRY("%p %d %p %zu %p %p %p\n", this, image_index, image,
>                   image_size, vendor_code, progress, abort_reason);
> @@ -747,10 +763,23 @@ efi_status_t EFIAPI efi_firmware_raw_set_image(
>                 }
>         }
>
> +       orig_dfu_env = env_get("dfu_alt_info");
> +       ret = env_set("dfu_alt_info", update_info.dfu_string);
> +       if (ret) {
> +               pr_err("unable to set env variable \"dfu_alt_info\"!\n");
> +               return -EINVAL;
> +       }
> +
>         if (dfu_write_by_alt(dfu_alt_num, (void *)image, image_size,
>                              NULL, NULL))
>                 return EFI_EXIT(EFI_DEVICE_ERROR);
>
> +       ret = env_set("dfu_alt_info", orig_dfu_env);
> +       if (ret) {
> +               pr_err("unable to set env variable \"dfu_alt_info\"!\n");
> +               return -EINVAL;
> +       }
> +
>         efi_firmware_set_fmp_state_var(&state, image_index);
>
>         return EFI_EXIT(EFI_SUCCESS);
> --
> 2.34.1
>