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

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Message-ID: <CAMzpN2jnyLGNvLbBjtc_U9C1D2nA8wqeGErUcS-HghD_vG6B9g@mail.gmail.com>
Date:	Thu, 23 Apr 2015 07:11:52 -0400
From:	Brian Gerst <brgerst@...il.com>
To:	Borislav Petkov <bp@...en8.de>
Cc:	Denys Vlasenko <dvlasenk@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Ingo Molnar <mingo@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andy Lutomirski <luto@...capital.net>,
	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
Subject: Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32_DS to %ss

On Thu, Apr 23, 2015 at 5:56 AM, Borislav Petkov <bp@...en8.de> wrote:
> On Thu, Apr 23, 2015 at 11:20:56AM +0200, Denys Vlasenko wrote:
>> * what if %ss before syscall was NOT the usual value of 0x2b, but some
>> other segment, not the typical 0-base, 0xffffffff limit 32-bit expand-up one?
>> Not restoring proper %ss would not go well.
>> [but then, Intel CPUs work, and old code worked....]
>
> Have we run the exact same reproducer on Intel already?
>
> Brian, can you run the same thing on an Intel box, if you haven't done
> so already?
>
> Thanks.

Tested it on a Intel(R) Core(TM)2 Duo CPU T6400 @ 2.00GHz and cannot
reproduce it there.  Note that on Intel CPUs, we use the sysenter VDSO
but return with sysret.

--
Brian Gerst
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