Received-SPF: pass (google.com: domain of linux-crypto-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 28 Nov 2022 01:19:36 +0100
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Samuel Neves <sneves@dei.uc.pt>
Cc:     Thomas Gleixner <tglx@linutronix.de>, linux-kernel@vger.kernel.org,
        patches@lists.linux.dev, linux-crypto@vger.kernel.org,
        linux-api@vger.kernel.org, x86@kernel.org,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>,
        Carlos O'Donell <carlos@redhat.com>,
        Florian Weimer <fweimer@redhat.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Christian Brauner <brauner@kernel.org>
Subject: Re: [PATCH v7 3/3] x86: vdso: Wire up getrandom() vDSO implementation
Message-ID: <Y4P+mOFu2A9tj5/y@zx2c4.com>
References: <20221124165536.1631325-1-Jason@zx2c4.com>
 <20221124165536.1631325-4-Jason@zx2c4.com>
 <874jumy6me.ffs@tglx>
 <Y4PfjcQRfezjH4f+@zx2c4.com>
 <CAEX_ruEq8_W8i-+cfri2-BYBNDgZCinsfFKVeFjxNSfnGxW1xg@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Disposition: inline
In-Reply-To: <CAEX_ruEq8_W8i-+cfri2-BYBNDgZCinsfFKVeFjxNSfnGxW1xg@mail.gmail.com>
Precedence: bulk

On Sun, Nov 27, 2022 at 10:39:27PM +0000, Samuel Neves wrote:
> On Sun, Nov 27, 2022 at 10:13 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> >
> > Hi Thomas,
> >
> > On Sat, Nov 26, 2022 at 12:08:41AM +0100, Thomas Gleixner wrote:
> > > Jason!
> > >
> > > On Thu, Nov 24 2022 at 17:55, Jason A. Donenfeld wrote:
> > > > +++ b/arch/x86/entry/vdso/vgetrandom-chacha.S
> > > > +/*
> > > > + * 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:
> > >
> > > Basic or not.
> >
> > Heh, FYI I didn't mean "basic" here as in "doesn't need a review", but
> > just that it's a straightforward technique and doesn't do any
> > complicated multiblock pyrotechnics (which frankly aren't really
> > needed).
> >
> > > This needs a Reviewed-by from someone who understands SSE2
> > > and ChaCha20 before this can go anywhere near the x86 tree.
> >
> > No problem. I'll see to it that somebody qualified gives this a review.
> >
> 
> I did look at this earlier. It looks fine. I would recommend changing
> 
> + /* copy1,copy2 = key */
> + movdqu 0x00(key),copy1
> + movdqu 0x10(key),copy2
> 
> to
> 
> + /* copy1,copy2 = key */
> + movups 0x00(key),copy1
> + movups 0x10(key),copy2
> 
> which has the same semantics, but saves a couple of code bytes. Likewise for
> 
> + movdqu state0,0x00(output)
> + movdqu state1,0x10(output)
> + movdqu state2,0x20(output)
> + movdqu state3,0x30(output)
> 
> Otherwise,
> 
> Reviewed-by: Samuel Neves <sneves@dei.uc.pt> # for vgetrandom-chacha.S

Thanks for the review and for the suggestion. Will do.

Jason