linux-kernel - Re: [PATCH 3/3] hwrng: Don't default to HW_RANDOM when UML

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Message-ID: <1b5988c648403676342b4340c3d78023@manjaro.org>
Date: Sun, 09 Feb 2025 10:37:52 +0100
From: Dragan Simic <dsimic@...jaro.org>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
 olivia@...enic.com, didi.debian@...ow.org, heiko@...ech.de
Subject: Re: [PATCH 3/3] hwrng: Don't default to HW_RANDOM when UML_RANDOM is
 the trigger

Hello Herbert,

On 2025-02-09 10:15, Herbert Xu wrote:
> On Wed, Jan 15, 2025 at 02:07:02PM +0100, Dragan Simic wrote:
>> Since the commit 72d3e093afae (um: random: Register random as 
>> hwrng-core
>> device), selecting the UML_RANDOM option may result in various 
>> HW_RANDOM_*
>> options becoming selected as well, which doesn't make much sense for 
>> UML
>> that obviously cannot use any of those HWRNG devices.
>> 
>> Let's have the HW_RANDOM_* options selected by default only when 
>> UML_RANDOM
>> actually isn't already selected.  With that in place, selecting 
>> UML_RANDOM
>> no longer "triggers" the selection of various HW_RANDOM_* options.
>> 
>> Fixes: 72d3e093afae (um: random: Register random as hwrng-core device)
>> Reported-by: Diederik de Haas <didi.debian@...ow.org>
>> Signed-off-by: Dragan Simic <dsimic@...jaro.org>
>> ---
>>  drivers/char/hw_random/Kconfig | 76 
>> +++++++++++++++++-----------------
>>  1 file changed, 38 insertions(+), 38 deletions(-)
>> 
>> diff --git a/drivers/char/hw_random/Kconfig 
>> b/drivers/char/hw_random/Kconfig
>> index e84c7f431840..283aba711af5 100644
>> --- a/drivers/char/hw_random/Kconfig
>> +++ b/drivers/char/hw_random/Kconfig
>> @@ -38,47 +38,47 @@ config HW_RANDOM_TIMERIOMEM
>>  config HW_RANDOM_INTEL
>>  	tristate "Intel HW Random Number Generator support"
>>  	depends on (X86 || COMPILE_TEST) && PCI
>> -	default HW_RANDOM
>> +	default HW_RANDOM if !UML_RANDOM
> 
> This is disgusting.  Just remove all the defaults, and we can
> add back the ones actually needed.  Just remember to set the
> default to something sane like HW_RANDOM && dependencies.

Could you, please, clarify why we need(ed) the defaults at all?
Also, I'm a bit puzzled about what would be the defaults that are
actually needed?  Are you actually referring to what I proposed
in my earlier response? [1]  I'd appreciate a clarification.

As a note, I tried to kind of "fix" it in a least intrusive way,
but I'll gladly have it fixed properly in the v2.  To me, getting
rid of the defaults completely would be the proper way.

[1] 
https://lore.kernel.org/linux-crypto/78b97c27314bfa1c7f0f17a90e623821@manjaro.org/