linux-kernel - Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32

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Message-ID: <20150423104401.GF28327@pd.tnic>
Date:	Thu, 23 Apr 2015 12:44:02 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Denys Vlasenko <dvlasenk@...hat.com>
Cc:	Andy Lutomirski <luto@...capital.net>,
	Brian Gerst <brgerst@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Will Drewry <wad@...omium.org>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kees Cook <keescook@...omium.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32_DS to
 %ss

On Thu, Apr 23, 2015 at 12:26:43PM +0200, Denys Vlasenko wrote:
> Yes. It loads *selector*. AMD docs say that selector is loaded as you say,
> but *cached descriptor* of SS (which is a different entity) is not modified.
> 
> If *cached descriptor* is invalid, in 32-bit mode stack ops
> will fail. (In 64-bit mode, CPU doesn't do those checks).

So how can that happen with wine? Something's changing the cached
descriptor and only the write to %ss reloads it with the correct value?

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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