linux-kernel - Re: [PATCH] ARC: ARCv2: jump label: implement jump label patching

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 for Android: free password hash cracker in your pocket

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

Message-ID: <20190620071514.GR3419@hirez.programming.kicks-ass.net>
Date:   Thu, 20 Jun 2019 09:15:14 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vineet Gupta <Vineet.Gupta1@...opsys.com>
Cc:     Eugeniy Paltsev <Eugeniy.Paltsev@...opsys.com>,
        "linux-snps-arc@...ts.infradead.org" 
        <linux-snps-arc@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexey Brodkin <Alexey.Brodkin@...opsys.com>,
        Jason Baron <jbaron@...mai.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH] ARC: ARCv2: jump label: implement jump label patching

On Wed, Jun 19, 2019 at 11:55:41PM +0000, Vineet Gupta wrote:

> FWIW I tried to avoid all of this by using the 2 byte NOP_S and B_S variants which
> ensures we can never straddle cache line so the alignment issue goes away. There's
> a nice code size reduction too - see [1] . But I get build link errors in
> networking code around DO_ONCE where the unlikely code is too much and offset
> can't be encoded in signed 10 bits which B_S is allowed.

Yeah, so on x86 we have a 2 byte and a 5 byte relative jump and have the
exact same issue. We're currently using 5 byte jumps unconditionally for
the same reason.

Getting it to use the 2 byte one where possible is a 'fun' project for
someone with spare time at some point.  It might need a GCC plugin to
pull off, I've not put too much tought into it.