Date: Thu, 23 Apr 2015 19:14:40 +0200
From: Borislav Petkov <bp@alien8.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Denys Vlasenko <vda.linux@googlemail.com>,
        Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>, Oleg Nesterov <oleg@redhat.com>,
        Ingo Molnar <mingo@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>, Will Drewry <wad@chromium.org>,
        =?utf-8?B?RnLDqWTDqXJpYw==?= Weisbecker <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" 
	<linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:x86/vdso] x86/vdso32/syscall.S: Do not load __USER32_DS to
 %ss
Message-ID: <20150423171440.GP28327@pd.tnic>
References: <tip-e7d6eefaaa443130079d73cd05039d90b3db7a4a@git.kernel.org>
 <CAMzpN2gD2kfKaXSYsXjZo=bLQYLk3A-sU_8qizfkp5paRuaePQ@mail.gmail.com>
 <CALCETrVH6STDwEuLY3gFaNevtjvtOZ7Ox3e10ZhtmitCJnJUKQ@mail.gmail.com>
 <5538C1C5.7010408@redhat.com>
 <20150423101840.GC28327@pd.tnic>
 <5538C8E3.60009@redhat.com>
 <20150423104401.GF28327@pd.tnic>
 <CALCETrW6E9qrVi-Qiri9eSVRDpDB6iFrqJMdu667cYdF-11YMw@mail.gmail.com>
 <CAK1hOcNTmAjVv5YHPSFUsA40y9dAoHPsQkKOTnYqqAf_gSs9Sg@mail.gmail.com>
 <CALCETrUHUJeVWC+qAwvrDF1dvPMY7jZcNNVh2gM77pw3db9JVg@mail.gmail.com>
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On Thu, Apr 23, 2015 at 09:50:17AM -0700, Andy Lutomirski wrote:
> On Thu, Apr 23, 2015 at 9:41 AM, Denys Vlasenko
> <vda.linux@googlemail.com> wrote:
> > An alternative fix would be, if we decided to schedule
> > in an interrupt, check %ss for zero and reload it
> > with __KERNEL_DS before schedule.
> 
> For anyone who has the right hardware (not me!), a possible reproducer is here:
> 
> https://git.kernel.org/cgit/linux/kernel/git/luto/misc-tests.git/
> 
> make && taskset -c 0 ./sysret_ss_attrs_32

[  195.438441] traps: sysret_ss_attrs[1745] trap stack segment ip:f77dab87 sp:ffdf0b70 error:0
[  196.831952] traps: sysret_ss_attrs[1748] trap stack segment ip:f7786b87 sp:fffc0810 error:0

Ran it twice.

-- 
Regards/Gruss,
    Boris.

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