linux-kernel - Re: [PATCH v2 2/4] MIPS: Introduce config options for LLSC availability

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.21.2406211827360.43454@angie.orcam.me.uk>
Date: Fri, 21 Jun 2024 18:40:19 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: Jiaxun Yang <jiaxun.yang@...goat.com>
cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>, 
    Jonas Gorski <jonas.gorski@...il.com>, 
    "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>, 
    linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] MIPS: Introduce config options for LLSC
 availability

On Fri, 21 Jun 2024, Jiaxun Yang wrote:

> >  That might do in the interim as a sanity check, however ultimately the 
> > sole reason these <asm/mach-*/cpu-feature-overrides.h> exist (and the 
> > `cpu_has_llsc' setting there) is so that a dynamic check at run time is 
> > avoided where the result is known from elsewhere beforehand anyway, and 
> > your change effectively supersedes the overrides, and therefore they need 
> > to be removed.
> >
> No, overrides are still valid if platform did CPU_MAY_HAVE_LLSC, this is at
> least valid for R10000 systems (IP28 decided to opt-out from llsc somehow),
> ATH25 (platform made assumption on IP version shipped with CPU), cavium
> octeon (platform decided to opt-out llsc for non-SMP build). I'm not confident
> with handling them all in Kconfig so I think the best approach so far is to do
> build time assertion.

 No, CPU_MAY_HAVE_LLSC is the dynamic case, in which case you need to run 
verification at run time and access the result via the CPU feature vector.  

 If you insist that you need a static override in this case, then you've 
got your CPU_MAY_HAVE_LLSC setting wrong, it should be either CPU_HAS_LLSC 
or nil, according to what <asm/mach-*/cpu-feature-overrides.h> currently 
sets for the platform in question.  Whatever is set statically there at 
build time can be reproduced in Kconfig.

 Going through platforms should be easy if not a bit tedious, but that's 
the cost you sometimes need to pay for progress.

  Maciej