[PATCH v2 1/1] efi_leader: delete rng-seed if having EFI RNG protocol

[Ilias Apalodimas]

Hi Heinrich,

On Tue, 17 Sept 2024 at 11:49, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
> For measured be boot we must avoid any volatile values in the device-tree.
> We already delete /chosen/kaslr-seed if we provide and EFI RNG protocol.
>
> Additionally remove /chosen/rng-seed provided by QEMU or U-Boot.
>
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
> ---
> v2:
>         Use an index instead of a position pointer for better readability
> ---
>  include/efi_loader.h          |  2 +-
>  lib/efi_loader/efi_dt_fixup.c | 15 ++++++++++-----
>  lib/efi_loader/efi_helper.c   |  2 +-
>  3 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/include/efi_loader.h b/include/efi_loader.h
> index f84852e384f..511281e150e 100644
> --- a/include/efi_loader.h
> +++ b/include/efi_loader.h
> @@ -567,7 +567,7 @@ efi_status_t EFIAPI efi_convert_pointer(efi_uintn_t debug_disposition,
>  /* Carve out DT reserved memory ranges */
>  void efi_carve_out_dt_rsv(void *fdt);
>  /* Purge unused kaslr-seed */
> -void efi_try_purge_kaslr_seed(void *fdt);
> +void efi_try_purge_rng_seed(void *fdt);
>  /* Called by bootefi to make console interface available */
>  efi_status_t efi_console_register(void);
>  /* Called by efi_init_obj_list() to proble all block devices */
> diff --git a/lib/efi_loader/efi_dt_fixup.c b/lib/efi_loader/efi_dt_fixup.c
> index 9d017804eea..0dac94b0c6c 100644
> --- a/lib/efi_loader/efi_dt_fixup.c
> +++ b/lib/efi_loader/efi_dt_fixup.c
> @@ -41,7 +41,7 @@ static void efi_reserve_memory(u64 addr, u64 size, bool nomap)
>  }
>
>  /**
> - * efi_try_purge_kaslr_seed() - Remove unused kaslr-seed
> + * efi_try_purge_rng_seed() - Remove unused kaslr-seed, rng-seed
>   *
>   * Kernel's EFI STUB only relies on EFI_RNG_PROTOCOL for randomization
>   * and completely ignores the kaslr-seed for its own randomness needs
> @@ -51,8 +51,9 @@ static void efi_reserve_memory(u64 addr, u64 size, bool nomap)
>   *
>   * @fdt: Pointer to device tree
>   */
> -void efi_try_purge_kaslr_seed(void *fdt)
> +void efi_try_purge_rng_seed(void *fdt)
>  {
> +       const char * const prop[] = {"kaslr-seed", "rng-seed"};
>         const efi_guid_t efi_guid_rng_protocol = EFI_RNG_PROTOCOL_GUID;
>         struct efi_handler *handler;
>         efi_status_t ret;
> @@ -67,9 +68,13 @@ void efi_try_purge_kaslr_seed(void *fdt)
>         if (nodeoff < 0)
>                 return;
>
> -       err = fdt_delprop(fdt, nodeoff, "kaslr-seed");
> -       if (err < 0 && err != -FDT_ERR_NOTFOUND)
> -               log_err("Error deleting kaslr-seed\n");
> +       for (size_t i = 0; i < ARRAY_SIZE(prop); ++i) {
> +               err = fdt_delprop(fdt, nodeoff, prop[i]);
> +               if (err < 0 && err != -FDT_ERR_NOTFOUND)
> +                       log_err("Error deleting %s\n", prop[i]);
> +               else
> +                       log_debug("Deleted /chosen/%s\n", prop[i]);
> +       }
>  }
>
>  /**
> diff --git a/lib/efi_loader/efi_helper.c b/lib/efi_loader/efi_helper.c
> index 96f847652ec..a481eb4b7e3 100644
> --- a/lib/efi_loader/efi_helper.c
> +++ b/lib/efi_loader/efi_helper.c
> @@ -522,7 +522,7 @@ efi_status_t efi_install_fdt(void *fdt)
>         /* Create memory reservations as indicated by the device tree */
>         efi_carve_out_dt_rsv(fdt);
>
> -       efi_try_purge_kaslr_seed(fdt);
> +       efi_try_purge_rng_seed(fdt);
>
>         if (CONFIG_IS_ENABLED(EFI_TCG2_PROTOCOL_MEASURE_DTB)) {
>                 ret = efi_tcg2_measure_dtb(fdt);
> --
> 2.45.2
>

I saw the comment on RISC-V. If there's size issues you are concerned,
I am fine with v2 as well -- just add a comment on why if you decide
to merge that

For v2 & v3
Reviewed-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>