linux-kernel - Re: [PATCH 2/2] x86_64,signal: Remove 'fs' and 'gs' from sigcontext

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Message-ID: <20140712183748.GW18735@two.firstfloor.org>
Date:	Sat, 12 Jul 2014 20:37:48 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	the arch/x86 maintainers <x86@...nel.org>
Subject: Re: [PATCH 2/2] x86_64,signal: Remove 'fs' and 'gs' from sigcontext

> This seems like it's asking for trouble.  I think wxe'd have to
> separately save the selectors and the base registers to avoid breaking
> something, especially once wrgsbase, etc are enabled.

I agree, it would likely break existing code.

> Linus, for context, the other patch in this series saves and restores
> SS. 

> Without that, 64-bit sigreturn to a nondefault stack segment is
> basically impossible.  

Why would you ever want to do that?

-Andi
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