From mboxrd@z Thu Jan 1 00:00:00 1970 From: joeyli Subject: Re: [PATCH v2 05/16] x86/efi: Get entropy through EFI random number generator protocol Date: Thu, 27 Aug 2015 14:17:50 +0800 Message-ID: <20150827061750.GE24088@linux-rxt1.site> References: <1439273796-25359-1-git-send-email-jlee@suse.com> <1439273796-25359-6-git-send-email-jlee@suse.com> <20150820202620.GF2567@codeblueprint.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20150820202620.GF2567-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org> Sender: linux-efi-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Matt Fleming Cc: "Lee, Chun-Yi" , linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-pm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, "Rafael J. Wysocki" , Matthew Garrett , Len Brown , Pavel Machek , Josh Boyer , Vojtech Pavlik , Matt Fleming , Jiri Kosina , "H. Peter Anvin" , Ingo Molnar List-Id: linux-pm@vger.kernel.org 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: > > + > > +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