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Date: Thu, 23 Apr 2015 07:11:52 -0400
Message-ID: <CAMzpN2jnyLGNvLbBjtc_U9C1D2nA8wqeGErUcS-HghD_vG6B9g@mail.gmail.com>
Subject: Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32_DS to %ss
From: Brian Gerst <brgerst@gmail.com>
To: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>, Steven Rostedt <rostedt@goodmis.org>,
        Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>, Will Drewry <wad@chromium.org>,
        =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-tip-commits@vger.kernel.org
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On Thu, Apr 23, 2015 at 5:56 AM, Borislav Petkov <bp@alien8.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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