From: David Laight <David.Laight@ACULAB.COM>
To: 'Kees Cook' <keescook@chromium.org>,
Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: Hsin-Yu.Chen <harry021633@gmail.com>,
"andy@kernel.org" <andy@kernel.org>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
"linux-hardening@vger.kernel.org"
<linux-hardening@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 2/2] string: improve strlen performance
Date: Sun, 5 May 2024 13:38:48 +0000 [thread overview]
Message-ID: <7c1565516531425c8f7cf5ffd5582741@AcuMS.aculab.com> (raw)
In-Reply-To: <202405020809.C8973634BF@keescook>
From: Kees Cook
> Sent: 02 May 2024 16:11
>
> On Thu, May 02, 2024 at 06:03:04PM +0300, Andy Shevchenko wrote:
> > On Thu, May 2, 2024 at 5:59 PM Andy Shevchenko
> > <andy.shevchenko@gmail.com> wrote:
> > > On Thu, May 2, 2024 at 5:14 PM Hsin-Yu.Chen <harry021633@gmail.com> wrote:
> >
> > And on top of that, check what this code will do on the architectures
> > that do not support unaligned access. If everything is fine, mention
> > this in the commit message. Btw, your commit message needs
> > elaboration, e.g., pointing to the test case (which is absent in this
> > patch, I assume it's already in the kernel?) and step-by-step
> > instructions on how you got the mentioned results with details of the
> > hardware you used for that.
>
> I might be worth looking at the implementation of strscpy(), which is
> doing similar multi-byte steps and handles unaligned access.
And x86 really doesn't care about unaligned accesses (for normal registers).
But it is important to not accidentally run off the end of a page.
There is also the whole question of the typical string length.
For short strings you've already lost by the time you've aligned
the address.
On 32bit the whole bit-twiddling may not be worth it at all.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
prev parent reply other threads:[~2024-05-05 13:39 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-02 14:13 [PATCH 2/2] string: improve strlen performance Hsin-Yu.Chen
2024-05-02 14:59 ` Andy Shevchenko
2024-05-02 15:03 ` Andy Shevchenko
2024-05-02 15:10 ` Kees Cook
2024-05-02 15:38 ` Andy Shevchenko
2024-05-05 13:38 ` David Laight [this message]
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