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

[Ilias Apalodimas <ilias.apalodimas@linaro.org>]

Hi Heinrich,

On Sat, Sep 14, 2024 at 06:08:12PM +0200, Heinrich Schuchardt 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@canonical.com>
> ---
> v2:
> 	put log_debug() in else branch
> ---
>  include/efi_loader.h          |  2 +-
>  lib/efi_loader/efi_dt_fixup.c | 16 +++++++++++-----
>  lib/efi_loader/efi_helper.c   |  2 +-
>  3 files changed, 13 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..b97758d1305 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 +68,14 @@ 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 (const char * const *pos = prop; pos < &prop[ARRAY_SIZE(prop)];

I think
for (int i = 0; i < ARRAY_SIZE(prop); i++)
    fdt_delprop(fdt, nodeoff, prop[i]);

is a lot easier to read

Other than that, the patch looks fine

Thanks
/Ilias

> +	     ++pos) {
> +		err = fdt_delprop(fdt, nodeoff, *pos);
> +		if (err < 0 && err != -FDT_ERR_NOTFOUND)
> +			log_err("Error deleting %s\n", *pos);
> +		else
> +			log_debug("Deleted /chosen/%s\n", *pos);
> +	}
>  }
>
>  /**
> 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
>