linux-kernel - Re: [PATCH v7 0/3] hwrng: add hwrng support for Rockchip RK3568

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Message-ID: <d5071401e8032af610c01a9d5887f186@manjaro.org>
Date: Wed, 17 Jul 2024 05:34:41 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: wens@...nel.org
Cc: Daniel Golle <daniel@...rotopia.org>, Diederik de Haas
 <didi.debian@...ow.org>, linux-rockchip@...ts.infradead.org,
 linux-arm-kernel@...ts.infradead.org, Rob Herring <robh@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, linux-kernel@...r.kernel.org, Herbert Xu
 <herbert@...dor.apana.org.au>, Martin Kaiser <martin@...ser.cx>, Sascha
 Hauer <s.hauer@...gutronix.de>, Sebastian Reichel
 <sebastian.reichel@...labora.com>, Ard Biesheuvel <ardb@...nel.org>,
 Uwe Kleine-König <ukleinek@...ian.org>,
 devicetree@...r.kernel.org, linux-crypto@...r.kernel.org, Philipp Zabel
 <p.zabel@...gutronix.de>, Olivia Mackall <olivia@...enic.com>, Krzysztof
 Kozlowski <krzk+dt@...nel.org>, Aurelien Jarno <aurelien@...el32.net>, Heiko
 Stuebner <heiko@...ech.de>, Anand Moon <linux.amoon@...il.com>
Subject: Re: [PATCH v7 0/3] hwrng: add hwrng support for Rockchip RK3568

Hello Chen-Yu,

On 2024-07-17 04:58, Chen-Yu Tsai wrote:
> On Wed, Jul 17, 2024 at 10:25 AM Daniel Golle <daniel@...rotopia.org> 
> wrote:
>> 
>> On Tue, Jul 16, 2024 at 07:19:35PM +0200, Diederik de Haas wrote:
>> > On Tuesday, 16 July 2024 18:53:43 CEST Diederik de Haas wrote:
>> > > rngtest: FIPS 140-2(2001-10-10) Long run: 0
>> >
>> > I don't know if it means something, but I noticed that I have
>> > ``Long run: 0`` with all my poor results,
>> > while Chen-Yu had ``Long run: 1``.
>> >
>> > Different SoC (RK3399), but Anand had ``Long run: 0`` too on their
>> > very poor result (100% failure):
>> > https://lore.kernel.org/linux-rockchip/CANAwSgTTzZOwBaR9zjJ5VMpxm5BydtW6rB2S7jg+dnoX8hAoWg@mail.gmail.com/
>> 
>> The conclusions I draw from that rather ugly situation are:
>>  - The hwrng should not be enabled by default, but it should by done
>>    for each board on which it is known to work well.
>>  - RK_RNG_SAMPLE_CNT as well as the assumed rng quality should be
>>    defined in DT for each board:
>>    * introduce new 'rochchip,rng-sample-count' property
>>    * read 'quality' property already used for timeriomem_rng
>> 
>> I will prepare a follow-up patch taking those conclusions into 
>> account.
>> 
>> Just for completeness, here my test result on the NanoPi R5C:
>> root@...nWrt:~# cat /dev/hwrng | rngtest -c 1000
>> rngtest 6.15
>> Copyright (c) 2004 by Henrique de Moraes Holschuh
>> This is free software; see the source for copying conditions.  There 
>> is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A 
>> PARTICULAR PURPOSE.
>> 
>> rngtest: starting FIPS tests...
>> rngtest: bits received from input: 20000032
>> rngtest: FIPS 140-2 successes: 875
>> rngtest: FIPS 140-2 failures: 125
>> rngtest: FIPS 140-2(2001-10-10) Monobit: 123
>> rngtest: FIPS 140-2(2001-10-10) Poker: 5
>> rngtest: FIPS 140-2(2001-10-10) Runs: 4
>> rngtest: FIPS 140-2(2001-10-10) Long run: 0
>> rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
>> rngtest: input channel speed: (min=85.171; avg=141.102; 
>> max=4882812.500)Kibits/s
>> rngtest: FIPS tests speed: (min=17.809; avg=19.494; 
>> max=60.169)Mibits/s
>> rngtest: Program run time: 139628605 microseconds
> 
> I doubt this is per-board. The RNG is inside the SoC, so it
> could be a chip quality thing.

Totally agreed.  I see no way how a board design could affect the
HWRNGs built into Rockchip SoCs.  I even checked the RK3399 and
RK3566 Hardware Design Guides to be extra sure.

> On the RK3399 we also saw wildly varying results.

In my opinion, that qualifies the RK3399's HWRNG as unsuitable for
general use.  Having a HWRNG that fails to pass the tests on _some_
units is simply not acceptable from the security standpoint.