linux-kernel - Re: [PATCH v4 0/4] x86: sigcontext fixes, again

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Date:	Tue, 16 Feb 2016 11:23:28 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	x86@...nel.org, Denys Vlasenko <dvlasenk@...hat.com>,
	Stas Sergeev <stsp@...t.ru>,
	Cyrill Gorcunov <gorcunov@...il.com>,
	Pavel Emelyanov <xemul@...allels.com>,
	Brian Gerst <brgerst@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v4 0/4] x86: sigcontext fixes, again

On Mon, Feb 15, 2016 at 06:38:12PM -0800, Andy Lutomirski wrote:
> This is take 2 at fixing x86 64-bit signals wrt SS.  After a lot of
> thought, this is not controlled by any flags -- I would much prefer
> to avoid opt-in behavior.  Instead, it just tries hard to avoid
> triggering the cases that break DOSEMU.
> 
> Stas, this now seems to pass the test you sent me.  It works with
> stock dosemu2 (I haven't tested classic dosemu because I can't get it
> to work regardless).  It also works with a patched dosemu2 that bypasses
> the userspace trampoline:
> 
> https://github.com/amluto/dosemu2/commit/571b4d08dc885b7a133e444a2ad23e0d21366206
> 
> With this applied, all of the x86 selftests pass on x86_64.  That
> wasn't the case before -- ldt_gdt_64 was broken.
> 
> This is a bit risky, and another option would be to do nothing at
> all.  Then we'd disable the problematic self-tests (sigh), and
> DOSEMU and similar tools will be stuck using gross hacks even on new
> kernels.
> 
> Changes from v3:
>  - Comment fixes from Borislav.
>  - Improve AR_xyz comments to better match SDM.  (Borislav, is this good?)

Yep, nice.

Thanks!

-- 
Regards/Gruss,
    Boris.

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