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From: Andy Lutomirski <luto@amacapital.net>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Andi Kleen <andi@firstfloor.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: [PATCH 2/2] x86_64,signal: Remove 'fs' and 'gs' from sigcontext
Date: Sat, 12 Jul 2014 01:39:01 -0700	[thread overview]
Message-ID: <CALCETrUqeUJT7xGy0TERVjJUAZUCXJGdgaDWv-f5+vkkArP8ig@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFxc1FWkSzRmtRP3XhEJ1Y1p8bc3SiTShhskwjRLJkTazA@mail.gmail.com>

On Jul 11, 2014 7:21 PM, "Linus Torvalds" <torvalds@linux-foundation.org> wrote:
>
> On Fri, Jul 11, 2014 at 9:29 AM, Andy Lutomirski <luto@amacapital.net> wrote:
> > As far as I can tell, these fields have been set to zero on save and
> > ignored on restore since Linux was imported into git.  Rename them
> > '__pad1' and '__pad2' to avoid confusion and to allow them to be
> > recycled some day.
>
> Shouldn't we actually try to save/restore gs/fs properly? Admittedly,
> changing them in the signal handler would be insane, but still.. See
> our context switching code  with the whole segment selector vs base
> save/restore code. Hmm?

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.

Why would this be needed anyway?

Does anyone implement makecontext, etc using raise/sigreturn?  If so,
they might be in for a surprise when their gs starts getting saved,
too.

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.  But I don't see why any other segments (besides
CS) are needed for 64-bit sigreturn.

--Andy

>
>             Linus

  parent reply	other threads:[~2014-07-12  8:39 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-07-11 16:29 [PATCH 0/2] x86_64,signal: Fix the set of saved segment registers Andy Lutomirski
2014-07-11 16:29 ` [PATCH 1/2] x86_64,signal: Save and restore SS in signal frames Andy Lutomirski
2015-03-09 20:15   ` Andy Lutomirski
2014-07-11 16:29 ` [PATCH 2/2] x86_64,signal: Remove 'fs' and 'gs' from sigcontext Andy Lutomirski
2014-07-11 18:12   ` Andi Kleen
2014-07-11 18:39     ` Andy Lutomirski
2014-07-12  2:09       ` H. Peter Anvin
2014-07-12  2:04   ` H. Peter Anvin
2014-07-12  2:21   ` Linus Torvalds
2014-07-12  2:26     ` H. Peter Anvin
2014-07-12  8:39     ` Andy Lutomirski [this message]
2014-07-12 18:37       ` Andi Kleen
2014-07-12 18:40         ` H. Peter Anvin
2014-07-12 18:52           ` Andi Kleen
2014-07-12 21:17             ` Andy Lutomirski
2014-07-18  1:13               ` Andy Lutomirski

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