linux-kernel - Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict Indirect Branch Speculation

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Message-ID: <20180126172712.e6iznttrqzfnwxyw@pd.tnic>
Date:   Fri, 26 Jan 2018 18:27:12 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Liran Alon <liran.alon@...cle.com>,
        Laura Abbott <labbott@...hat.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        "Mallick, Asit K" <asit.k.mallick@...el.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        KarimAllah Ahmed <karahmed@...zon.de>,
        Peter Anvin <hpa@...or.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ashok Raj <ashok.raj@...el.com>,
        "Van De Ven, Arjan" <arjan.van.de.ven@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        KVM list <kvm@...r.kernel.org>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation

On Fri, Jan 26, 2018 at 09:19:09AM -0800, Linus Torvalds wrote:
> But did we do that "disable stuffing with SMEP"? I'm not seeing it. In
> my tree, it's only conditional on X86_FEATURE_RETPOLINE.

Or rather, enable stuffing on !SMEP:

+       if ((!boot_cpu_has(X86_FEATURE_PTI) &&
+            !boot_cpu_has(X86_FEATURE_SMEP)) || is_skylake_era()) {
+               setup_force_cpu_cap(X86_FEATURE_RSB_CTXSW);
+               pr_info("Filling RSB on context switch\n");
+       }

Should be

c995efd5a740 ("x86/retpoline: Fill RSB on context switch for affected CPUs")

in your tree.

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
--