linux-kernel - Re: [patch 15/24] x86/speculation: Add command line control for indirect branch speculation

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]

Date:   Thu, 22 Nov 2018 09:14:47 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>
cc:     Tom Lendacky <thomas.lendacky@....com>,
        LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Stewart <david.c.stewart@...el.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 15/24] x86/speculation: Add command line control for
 indirect branch speculation

On Thu, 22 Nov 2018, Borislav Petkov wrote:
> > +
> > +	/* Initialize Indirect Branch Prediction Barrier */
> > +	if (boot_cpu_has(X86_FEATURE_IBPB)) {
> > +		setup_force_cpu_cap(X86_FEATURE_USE_IBPB);
> > +		pr_info("Spectre v2 mitigation: Enabling Indirect Branch Prediction Barrier\n");
> > +	}
> 
> So AFAICT, if coming in here with AUTO, we won't enable IBPB and I
> *think* AMD wants IBPB enabled. At least the whitepaper says:
> 
> "IBPB combined with Reptoline software support is the AMD recommended
> setting for Linux mitigation of Google Project Zero Variant 2
> (Spectre)."

Ok. That's indeed a step backwards, because we don't do IBPB in KVM
anymore. I'll fix that tomorrow morning when brain is more awake.

IBPB on context switch is controlled separately anyway now, so that's a
nobrainer to sort out.

Though I wait for Toms answer whether we really want IBPB on context switch
for AMD by default.

Thanks,

	tglx