[PATCH] efi_loader: Bump the number of shared pages with StandAloneMM

[Heinrich Schuchardt]

On 12/15/21 08:50, Ilias Apalodimas wrote:
> Currently we allow (and explicitly check) a single shared page with
> StandAloneMM.  This is dictated by OP-TEE which runs the application.
> However there's no way for us dynamically discover the number of pages we
> are allowed to use.  Since writing big EFI signature list variables
> requires more than a page, OP-TEE has bumped the number of shared pages to
> four.  Bump our page checks to four as well.
>
> Note here that checking some kind of version and reason with the
> compatibility doesn't make too much sense.  We sanitize the number of pages
> internally in our U-Boot code but eventually OP-TEE will fail if we try to
> write more than it's allowing. The error will just happen later on when we
> access StandAloneMM.  So in order to avoid compatibility checks change the
> number to four unconditionally.
>
> Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
> Tested-by: Ying-Chun Liu (PaulLiu) <paul.liu at linaro.org>
> ---
>   lib/efi_loader/efi_variable_tee.c | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/lib/efi_loader/efi_variable_tee.c b/lib/efi_loader/efi_variable_tee.c
> index 281f886124af..95eaeaa5fd9d 100644
> --- a/lib/efi_loader/efi_variable_tee.c
> +++ b/lib/efi_loader/efi_variable_tee.c
> @@ -261,8 +261,8 @@ efi_status_t EFIAPI get_max_payload(efi_uintn_t *size)
>   	 * with StMM. Since OP-TEE will reject to map anything bigger than that,
>   	 * make sure we are in bounds.
>   	 */
> -	if (*size > OPTEE_PAGE_SIZE)
> -		*size = OPTEE_PAGE_SIZE - MM_COMMUNICATE_HEADER_SIZE  -
> +	if (*size > 4 * OPTEE_PAGE_SIZE)
> +		*size = 4 * OPTEE_PAGE_SIZE - MM_COMMUNICATE_HEADER_SIZE  -
>   			MM_VARIABLE_COMMUNICATE_SIZE;

Why do we need this check at all if OPTEE checks again?

Best regards

Heinrich

>   	/*
>   	 * There seems to be a bug in EDK2 miscalculating the boundaries and