linux-kernel - Re: [PATCH] x86/shstk: Enable shadow stack for x32

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Date: Fri, 22 Mar 2024 08:06:34 -0700
From: "H.J. Lu" <hjl.tools@...il.com>
To: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH] x86/shstk: Enable shadow stack for x32

On Fri, Mar 22, 2024 at 7:07 AM Edgecombe, Rick P
<rick.p.edgecombe@...el.com> wrote:
>
> On Fri, 2024-03-15 at 07:34 -0700, H.J. Lu wrote:
> > > How many people do you think will use this?
>
> I'm concerned that the only use of this will ever be exercise via the
> glibc unit tests, but will still require work to support.

 Correct.  A small glibc change is needed.  Will post it after
my kernel change is merged.

> > >
> > > I would have thought it would require more changes for basic x32
> >
> > This is all needed.
> >
> > > operation. What was the testing exactly?
> >
> > I configured x32 glibc with --enable-cet, build glibc and
> > run all glibc tests with shadow stack enabled.  There are
> > no regressions.  I verified that shadow stack is enabled
> > via /proc/pid/status.
>
> The shadow stack is supposed to be mapped above 4G, so how is this
> supposed to work for x32?

This is not what I see:

(gdb) info reg
..
pl3_ssp        0xf7dcbfe8          0xf7dcbfe8

--
H.J.