linux-kernel - Re: [PATCH 20/35] x86: Force asm-goto

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: <1516292748.4937.159.camel@infradead.org>
Date:   Thu, 18 Jan 2018 17:25:48 +0100
From:   David Woodhouse <dwmw2@...radead.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Dave Hansen <dave.hansen@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Arjan Van De Ven <arjan.van.de.ven@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH 20/35] x86: Force asm-goto

On Thu, 2018-01-18 at 14:48 +0100, Peter Zijlstra wrote:
> Now that we have objtool to validate the correctness of asm-goto
> constructs we can start using it to guarantee the absence of dynamic
> branches (and thus speculation).
> 
> A primary prerequisite for this is of course that the compiler
> supports asm-goto. This effecively lifts the minimum GCC version to
> build an x86 kernel to gcc-4.5.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

This is cute, but it's the wrong way round. We *know* people will be
immediately backporting this to every stable kernel they're still
using.

Let's put it in using alternatives (or the 'else lfence' version,
even), and then clean it up with static_cpu_has() on *top* of that, so
that the latter doesn't have to be backported.
Download attachment "smime.p7s" of type "application/x-pkcs7-signature" (5213 bytes)