linux-kernel - RE: [PATCH 14/15] x86/fsgsbase/64: Support legacy behavior when FS/GS updated by ptracer

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Message-ID: <C9BB696F3A938947B10DCAD29FAB8FFA66AC932C@CRSMSX101.amr.corp.intel.com>
Date:   Thu, 22 Mar 2018 21:17:49 +0000
From:   "Bae, Chang Seok" <chang.seok.bae@...el.com>
To:     Andy Lutomirski <luto@...nel.org>
CC:     X86 ML <x86@...nel.org>, Andi Kleen <ak@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        "Metzger, Markus T" <markus.t.metzger@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 14/15] x86/fsgsbase/64: Support legacy behavior when
 FS/GS updated by ptracer


________________________________________
From: Andy Lutomirski [luto@...nel.org]
Sent: Thursday, March 22, 2018 09:53
>>> But your patch doesn't actually do this, since gdb will just do
>>> SETREGS anyway, right?
>> GDB does SETREGS on any exclusive (FS/GS) updates in inferior call.

> This means that your patch has exactly the same effect as the code in
> my git tree, right?  Then let's stick with something like what's in my
> git tree, since it's far simpler.

Difference is if flipping FS/GS multiple times, user may check the base from LDT.
But I don't have strong will to keep arguing this; Markus or somebody might 
want to say something.

The whole point as I understand is to avoid any regression on legacy ptracers.
If a strong confidence lies on the simple version, let me. My first thought bought
this in fact.

Thanks,
Chang