linux-kernel - Re: [BUG] x86 : i486 reporting to be vulnerable to Meltdown/Spectre_V1/Spectre

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Message-ID: <20180208134908.4b516794@alans-desktop>
Date:   Thu, 8 Feb 2018 13:49:08 +0000
From:   Alan Cox <gnomes@...rguk.ukuu.org.uk>
To:     Ondrej Zary <linux@...nbow-software.org>
Cc:     whiteheadm@....org, David Woodhouse <dwmw2@...radead.org>,
        Guenter Roeck <linux@...ck-us.net>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Hugh Dickins <hughd@...gle.com>, dave.hansen@...ux.intel.com,
        jikos@...nel.org, Borislav Petkov <bp@...en8.de>,
        Kees Cook <keescook@...omium.org>,
        Jamie Iles <jamie@...ieiles.com>, eduval@...zon.com,
        labbott@...hat.com, Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [BUG] x86 : i486 reporting to be vulnerable to
 Meltdown/Spectre_V1/Spectre_V2

> What about Pentium II and 3? I'm using 5 such machines (and also a Pentium 
> MMX). I've tried a spectre test before and it wasn't reading anything useful. 
> Don't know about meltdown. Is there a complete test program? (The web is so 
> full of crap that even google can't find anything useful.)

Pentium MMX does not speculate. Pentium II does.

For meltdown there are some reasonably easy tests to run to look for a
positive. Proving a negative is much much harder however and as far as I
am aware nobody has done a full evaluation of processors that old.

For x86 speculation came in (as far as I can tell) in

AMD Am5x86
Cyrix 5x86, but branch predictors are disabled by default according to
the docs
Cyrix 6x86, branch prediction on by default
Pentium Pro

There are later processors that don't have speculation: Quark series, Nat
Semi/Cyrix Geode, earliest AMD geode (I think), some Intel Atom
processors.

The more obscure ones - the Transmeta apparently may, the IDT Winchip
documentation strongly implies it doesn't, the Vortex86 (aka
SiS55X/Rise mP6) says it doesn't and things like the NexGen I have no
idea about.

The problem is that it's very hard to definitively answer questions on
these processors and vulnerabilities like they are obsolete, almost
nobody uses them for anything but retro stuff and the return on the effort
of figuring out defiitive answers is close to nil.

Alan