linux-kernel - Re: [PATCH v1 3/8] x86/entry/clearregs: Clear registers for 64bit SYSCALL

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: <20180111184750.y42sv4hn7e3r3f3k@two.firstfloor.org>
Date:   Thu, 11 Jan 2018 10:47:50 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     Brian Gerst <brgerst@...il.com>
Cc:     Andi Kleen <andi@...stfloor.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Paul Turner <pjt@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jiri Kosina <jikos@...nel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1 3/8] x86/entry/clearregs: Clear registers for 64bit
 SYSCALL

On Wed, Jan 10, 2018 at 10:35:58PM -0500, Brian Gerst wrote:
> > @@ -263,6 +271,7 @@ entry_SYSCALL_64_fastpath:
> >  #endif
> >         ja      1f                              /* return -ENOSYS (already in pt_regs->ax) */
> >         movq    %r10, %rcx
> > +       xor     %r10, %r10
> 
> RCX is already clear, so xchgq %r10, %rcx will be simpler.

XOR is special cased by the hardware, so it's always more
efficient.

-Andi
>