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

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Message-ID: <CAHmME9o35OwD574x2TyAfp=iRfWD95pvi561+Q=2aAWRORofKg@mail.gmail.com>
Date: Tue, 27 Aug 2024 17:16:16 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>
Cc: Adhemerval Zanella <adhemerval.zanella@...aro.org>, "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>
Subject: Re: [PATCH] aarch64: vdso: Wire up getrandom() vDSO implementation

On Tue, Aug 27, 2024 at 11:02 AM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> On Tue, Aug 27, 2024 at 10:46:21AM +0200, Christophe Leroy wrote:
> > > +/**
> > > + * __arch_chacha20_blocks_nostack - Generate ChaCha20 stream without using the stack.
> > > + * @dst_bytes:     Destination buffer to hold @nblocks * 64 bytes of output.
> > > + * @key:   32-byte input key.
> > > + * @counter:       8-byte counter, read on input and updated on return.
> > > + * @nblocks:       Number of blocks to generate.
> > > + *
> > > + * Generates a given positive number of blocks of ChaCha20 output with nonce=0, and does not write
> > > + * to any stack or memory outside of the parameters passed to it, in order to mitigate stack data
> > > + * leaking into forked child processes.
> > > + */
> > > +extern void __arch_chacha20_blocks_nostack(u8 *dst_bytes, const u32 *key, u32 *counter, size_t nblocks);
> >
> > For Jason: We all redefine this prototype, should we have it in a
> > central place, or do you expect some architecture to provide some static
> > inline for it ?
>
> Given the doc comment and such, that would be nice. But I didn't see a
> straight forward way of doing that when I tried before. If you want to
> try and send another fixup commit, that'd be welcomed.

I'll give it a shot.