linux-kernel - Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines

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: <CALCETrXFDtZ9qkyaPTNqos+=Q8iDSxbjaC36ikg5dJBc8+sToA@mail.gmail.com>
Date:	Sat, 12 Mar 2016 09:21:16 -0800
From:	Andy Lutomirski <luto@...capital.net>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Fenghua Yu <fenghua.yu@...el.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"x86@...nel.org" <x86@...nel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"Bryan O'Donoghue" <pure.logic@...us-software.ie>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Yu, Yu-cheng" <yu-cheng.yu@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/FPU: Fix FPU handling on legacy FPU machines

On Mar 11, 2016 2:20 PM, "Borislav Petkov" <bp@...en8.de> wrote:
>
> On Fri, Mar 11, 2016 at 02:07:19PM -0800, Dave Hansen wrote:
> > I've actually got 4.0 running on my Quark board.  The FPU rewrite
> > dropped in just after that iirc.
>
> 4.2 or so... Ok, so it looks like we broke it then.
>

For reference, what are the QEMU options and boot options you used to
trigger this?  I'm asking because I tested eagerfpu=on without fxsr a
few weeks ago in QEMU, and I didn't trigger it.  Maybe I needed to
force KVM off or something.  Off the top of my head, I'm guessing that
when I wrote "x86/fpu: Fix FNSAVE usage in eagerfpu mode", I was
inadvertently using a bastardize combination of FNSAVE and
FXRSTOR-of-init-state, KVM let the FXRSTOR through despite not
advertising it in CPUID, and it papered over the init issue because
the wrong init state format was hidden by using the wrong instruction
to load it.

Sigh.  Yet more reason for Intel to add chicken bits to *turn off* new features.

--Andy