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

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Date: Fri, 22 Mar 2024 14:28:15 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "hjl.tools@...il.com" <hjl.tools@...il.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, 2024-03-22 at 07:07 -0700, Rick Edgecombe 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.

To elaborate more on this... The main usage of shadow stack is
security, and comes with some overhead. IIUC the main usage of x32 is
performance benchmarking type stuff. Why would someone want to use
shadow stack and x32 together?

> 
> > > 
> > > 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?