On Thu, Aug 20, 2015 at 09:26:20PM +0100, Matt Fleming wrote:

On Tue, 11 Aug, at 02:16:25PM, Lee, Chun-Yi wrote:

quoted

+
+static unsigned long efi_get_rng64(efi_system_table_t *sys_table,
+				   void **rng_handle)
+{
+	const struct efi_config *efi_early = __efi_early();
+	efi_rng_protocol_64 *rng = NULL;
+	efi_guid_t rng_proto = EFI_RNG_PROTOCOL_GUID;
+	u64 *handles = (u64 *)(unsigned long)rng_handle;
+	efi_status_t status;
+	unsigned long rng_number;
+
+	status = efi_call_early(handle_protocol, handles[0],
+				&rng_proto, (void **)&rng);
+	if (status != EFI_SUCCESS)
+		efi_printk(sys_table, "Failed to get EFI_RNG_PROTOCOL handles\n");
+
+	if (status == EFI_SUCCESS && rng) {
+		status = efi_early->call((unsigned long)rng->get_rng, rng, NULL,
+					sizeof(rng_number), &rng_number);

Actually, one thing just occurred to me - you're not passing an
RNGAlgorithm value and are relying upon the firmware's default
implementation.

I don't think that's a safe bet, the default could be anything and
might vary across implementations.

I didn't set specific RNGAlgorithm because different BIOS may
set different algorithm as default, it's also a kind of random situation
to provide uncertainty.

On the other hand, if the specific RNGAlgorithm doesn't support by BIOS
then EFI stub still need use BIOS's _default_ algorithm to get random
value.

Can we do a little better here and pick a "preferred" algorithm
instead of the default?

-- 
Matt Fleming, Intel Open Source Technology Center

Per EDK2 implementation, EFI_RNG_ALGORITHM_SP800_90_CTR_256 is the default
algorithm that provided by driver, and EFI_RNG_ALGORITHM_RAW is the second
algorithm supported by EDK2. BIOS vendor need to write driver to support
others.

Maybe using EFI_RNG_ALGORITHM_SP800_90_CTR_256 as the default RNGAlgorithm
in efi_random can cover the most widely UEFI implementation, but when BIOS
do not support EFI_RNG_ALGORITHM_SP800_90_CTR_256 then kernel still need
use BIOS's _default_ setting.

I hope your suggestion.


Thanks a lot!
Joey Lee