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

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Message-ID: <CA+55aFwoxXmY0u84iPT-RP8DoG+Qb8t-mh2r8RLhKVAH3jm6qg@mail.gmail.com>
Date:   Sun, 21 Jan 2018 14:27:58 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     KarimAllah Ahmed <karahmed@...zon.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "H . Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Laura Abbott <labbott@...hat.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        KVM list <kvm@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>
Subject: Re: [RFC 09/10] x86/enter: Create macros to restrict/unrestrict
 Indirect Branch Speculation

On Sun, Jan 21, 2018 at 2:00 PM, David Woodhouse <dwmw2@...radead.org> wrote:
>>
>> The patches do things like add the garbage MSR writes to the kernel
>> entry/exit points. That's insane. That says "we're trying to protect
>> the kernel".  We already have retpoline there, with less overhead.
>
> You're looking at IBRS usage, not IBPB. They are different things.

Ehh. Odd intel naming detail.

If you look at this series, it very much does that kernel entry/exit
stuff. It was patch 10/10, iirc. In fact, the patch I was replying to
was explicitly setting that garbage up.

And I really don't want to see these garbage patches just mindlessly
sent around.

                  Linus