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From:   Florian Weimer <fweimer@redhat.com>
To:     Cristian =?utf-8?Q?Rodr=C3=ADguez?= <crrodriguez@opensuse.org>
Cc:     "Jason A. Donenfeld" <Jason@zx2c4.com>, libc-alpha@sourceware.org,
        Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>,
        Yann Droneaud <ydroneaud@opteya.com>, jann@thejh.net,
        Michael@phoronix.com, linux-crypto@vger.kernel.org
Subject: Re: arc4random - are you sure we want these?
References: <YtwgTySJyky0OcgG@zx2c4.com> <Ytwg8YEJn+76h5g9@zx2c4.com>
        <CAPBLoAdtEcpJg7sZQ7+z7HeCQzAs7Am7ep9GBFuBGxUeC3NyEw@mail.gmail.com>
Date:   Mon, 25 Jul 2022 12:14:08 +0200
In-Reply-To: <CAPBLoAdtEcpJg7sZQ7+z7HeCQzAs7Am7ep9GBFuBGxUeC3NyEw@mail.gmail.com>
        ("Cristian =?utf-8?Q?Rodr=C3=ADguez=22's?= message of "Sat, 23 Jul 2022
 15:04:36 -0400")
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* Cristian Rodr=C3=ADguez:

> On Sat, Jul 23, 2022 at 12:25 PM Jason A. Donenfeld via Libc-alpha
> <libc-alpha@sourceware.org> wrote:
>
>> For that reason, past discussion of having some random number generation
>> in userspace libcs has geared toward doing this in the vDSO, somehow,
>> where the kernel can be part and parcel of that effort.
>
> On linux just making this interface call "something" from the VDSO that
>
> - does not block.
> - cannot ever fail or if it does indeed need to bail out it kills the
> calling thread as last resort.
>
> (if neither of those can be provided, we are back to square one)
>
> Will be beyond awesome because it could be usable everywhere,
> including the dynamic linker, malloc or whatever else
> question is..is there any at least experimental patch  with a hope of
> beign accepted available ?

I agree that this would be nice, but we'd like have to donate
thread-specific data for kernel use, and that's currently totally
vaporware.

The =E2=80=9Ccannot ever fail=E2=80=9D part is impossible to achieve due to=
 old kernels
and seccomp filters.  Low-level userspace needs to paper over it in some
way, so that applications don't have to deal with it.

Thanks,
Florian