linux-kernel - Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support

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, 04 Jan 2018 19:27:58 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>,
        One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Subject: Re: [PATCH v3 01/13] x86/retpoline: Add initial retpoline support

On Thu, 2018-01-04 at 10:36 -0800, Alexei Starovoitov wrote:
> 
> Pretty much.
> Paul's writeup: https://support.google.com/faqs/answer/7625886
> tldr: jmp *%r11 gets converted to:
> call set_up_target;
> capture_spec:
>   pause;
>   jmp capture_spec;
> set_up_target:
>   mov %r11, (%rsp);
>   ret;
> where capture_spec part will be looping speculatively.

That is almost identical to what's in my latest patch set, except that
the capture_spec loop has 'lfence' instead of 'pause'.

As Andi says, I'd want to see explicit approval from the CPU architects
for making that change.

We've already had false starts there — for a long time, Intel thought
that a much simpler option with an lfence after the register load was
sufficient, and then eventually worked out that in some rare cases it
wasn't. While AMD still seem to think it *is* sufficient for them,
apparently.
Download attachment "smime.p7s" of type "application/x-pkcs7-signature" (5213 bytes)