linux-kernel - Re: [PATCH v10 4/4] x86: vdso: Wire up getrandom() vDSO implementation

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Date:   Tue, 29 Nov 2022 21:22:11 -0800
From:   Eric Biggers <ebiggers@...nel.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     linux-kernel@...r.kernel.org, patches@...ts.linux.dev,
        tglx@...utronix.de, 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>,
        Arnd Bergmann <arnd@...db.de>,
        Christian Brauner <brauner@...nel.org>,
        Samuel Neves <sneves@....uc.pt>
Subject: Re: [PATCH v10 4/4] x86: vdso: Wire up getrandom() vDSO
 implementation

On Tue, Nov 29, 2022 at 10:06:39PM +0100, Jason A. Donenfeld wrote:
> diff --git a/arch/x86/entry/vdso/vgetrandom-chacha.S b/arch/x86/entry/vdso/vgetrandom-chacha.S
> new file mode 100644
> index 000000000000..91fbb7ac7af4
> --- /dev/null
> +++ b/arch/x86/entry/vdso/vgetrandom-chacha.S
> @@ -0,0 +1,177 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2022 Jason A. Donenfeld <Jason@...c4.com>. All Rights Reserved.
> + */
> +
> +#include <linux/linkage.h>
> +#include <asm/frame.h>
> +
> +.section	.rodata.cst16.CONSTANTS, "aM", @progbits, 16
> +.align 16
> +CONSTANTS:	.octa 0x6b20657479622d323320646e61707865
> +.text
> +
> +/*
> + * Very basic SSE2 implementation of ChaCha20. Produces a given positive number
> + * of blocks of output with a nonce of 0, taking an input key and 8-byte
> + * counter. Importantly does not spill to the stack. Its arguments are:
> + *
> + *	rdi: output bytes
> + *	rsi: 32-byte key input
> + *	rdx: 8-byte counter input/output
> + *	rcx: number of 64-byte blocks to write to output
> + */
> +SYM_FUNC_START(__arch_chacha20_blocks_nostack)

How was this ChaCha20 implementation tested?

It really ought to have some sort of test.

Wouldn't this be a good candidate for a KUnit test?

- Eric