linux-kernel - Re: [PATCH v2] aarch64: vdso: Wire up getrandom() vDSO implementation

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Message-ID: <ZtDeGbgdpeI082i6@zx2c4.com>
Date: Thu, 29 Aug 2024 22:46:17 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Adhemerval Zanella <adhemerval.zanella@...aro.org>
Cc: Theodore Ts'o <tytso@....edu>, linux-kernel@...r.kernel.org,
	linux-crypto@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-arch@...r.kernel.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, Thomas Gleixner <tglx@...utronix.de>,
	Eric Biggers <ebiggers@...nel.org>,
	Christophe Leroy <christophe.leroy@...roup.eu>
Subject: Re: [PATCH v2] aarch64: vdso: Wire up getrandom() vDSO implementation

Hi Catalin, Will, Adhemerval,

On Thu, Aug 29, 2024 at 08:17:14PM +0000, Adhemerval Zanella wrote:
> Hook up the generic vDSO implementation to the aarch64 vDSO data page.
> The _vdso_rng_data required data is placed within the _vdso_data vvar
> page, by using a offset larger than the vdso_data.
> 
> The vDSO function requires a ChaCha20 implementation that does not
> write to the stack, and that can do an entire ChaCha20 permutation.
> The one provided is based on the current chacha-neon-core.S and uses NEON
> on the permute operation. The fallback for chips that do not support
> NEON issues the syscall.
> 
> This also passes the vdso_test_chacha test along with
> vdso_test_getrandom. The vdso_test_getrandom bench-single result on
> Neoverse-N1 shows:
> 
>    vdso: 25000000 times in 0.746506464 seconds
>    libc: 25000000 times in 8.849179444 seconds
> syscall: 25000000 times in 8.818726425 seconds

Aside from the big endian concerns we discussed on IRC, this is looking
fine to me, and I'd like to get some variant of this queued up in my
random.git tree for 6.12 soon.

But first, Catalin or Will -- could one of you take a look and provide
your Acked-by for that, if the patch looks good to you?

Thanks,
Jason