linux-kernel - Re: [PATCH] random: remove CONFIG_ARCH

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Date:   Tue, 05 Jul 2022 16:11:45 -0700
From:   "H. Peter Anvin" <hpa@...or.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "Jason A. Donenfeld" <Jason@...c4.com>,
        linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] random: remove CONFIG_ARCH_RANDOM and "nordrand"

On July 5, 2022 3:00:04 PM PDT, Borislav Petkov <bp@...en8.de> wrote:
>On Tue, Jul 05, 2022 at 02:50:34PM -0700, H. Peter Anvin wrote:
>> It's just math. The only variable is your confidence level, i.e. at
>> what level do you decide that the likelihood of pure chance is way
>> smaller than the likelihood of hardware failure.
>
>That might be but the likelyhood of certain BIOSes dropping the ball
>after resume is 100%:
>
>7879fc4bdc75 ("x86/rdrand: Sanity-check RDRAND output")
>

What I'm wondering is if we shouldn't be simply instrument *every* invocation, and set the trust to zero if we ever trip it.