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
| ||
|
Date: Fri, 28 Aug 2020 08:41:18 +0200 From: Uros Bizjak <ubizjak@...il.com> To: Al Viro <viro@...iv.linux.org.uk> Cc: X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com> Subject: Re: [PATCH v2] x86: Use xorl %0,%0 in __get_user_asm On Thu, Aug 27, 2020 at 10:14 PM Al Viro <viro@...iv.linux.org.uk> wrote: > > On Thu, Aug 27, 2020 at 08:09:04PM +0200, Uros Bizjak wrote: > > xorl %0,%0 is equivalent to xorq %0,%0 as both will zero the > > entire register. Use xorl %0,%0 for all operand sizes to avoid > > REX prefix byte when legacy registers are used and to avoid size > > prefix byte when 16bit registers are used. > > > > Zeroing the full register is OK in this use case. xorl %0,%0 also > > breaks register dependency chains, avoiding potential partial > > register stalls with 8 and 16bit operands. > > No objections, but talking about stalls is more than slightly > ridiculous - we'd just taken a #PF, failed there, flipped > pt_regs %rip to fixup section, returned from fault and are > about to fail whatever syscall that had been; a stall here > is really not an issue... Should I submit a v3 with the offending sentence removed, or could I just ask a committer to remove it on the fly? Uros.
Powered by blists - more mailing lists