linux-kernel - Re: [PATCH v8 3/3] x86: vdso: Wire up getrandom() vDSO implementation

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Message-Id: <8f9326ba-f879-4b9e-9e5d-b65cad7cd726@app.fastmail.com>
Date:   Mon, 28 Nov 2022 20:18:12 +0100
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Jason A . Donenfeld" <Jason@...c4.com>,
        linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        "Thomas Gleixner" <tglx@...utronix.de>
Cc:     linux-crypto@...r.kernel.org, linux-api@...r.kernel.org,
        x86@...nel.org, "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        "Adhemerval Zanella Netto" <adhemerval.zanella@...aro.org>,
        "Carlos O'Donell" <carlos@...hat.com>,
        "Florian Weimer" <fweimer@...hat.com>,
        "Christian Brauner" <brauner@...nel.org>,
        "Samuel Neves" <sneves@....uc.pt>
Subject: Re: [PATCH v8 3/3] x86: vdso: Wire up getrandom() vDSO implementation

On Mon, Nov 28, 2022, at 12:18, Jason A. Donenfeld wrote:
> Hook up the generic vDSO implementation to the x86 vDSO data page. Since
> the existing vDSO infrastructure is heavily based on the timekeeping
> functionality, which works over arrays of bases, a new macro is
> introduced for vvars that are not arrays.
>
> Also enable the vgetrandom_alloc() syscall, which the vDSO
> implementation relies on.
>
> The vDSO function requires a ChaCha20 implementation that does not write
> to the stack, yet can still do an entire ChaCha20 permutation, so
> provide this using SSE2, since this is userland code that must work on
> all x86-64 processors.
>
> Reviewed-by: Samuel Neves <sneves@....uc.pt> # for vgetrandom-chacha.S
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  arch/x86/Kconfig                        |   1 +
>  arch/x86/entry/syscalls/syscall_64.tbl  |   1 +

I see that this enables the syscall in x86-64, while patch 1
adds it to the eight architecures that use 
include/uapi/asm-generic/unistd.h (with the __ARCH_WANT_*
guard at the moment, but you already said that will be removed)

I think ideally the syscall.tbl and unistd.h changes should be done
in one patch for all architectures that doesn't mix it with
any other changes. In particular I think it should be separate
from the vdso changes, but could be in the patch that implements
the syscall.

      Arnd