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

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Message-ID: <CALCETrUHUJeVWC+qAwvrDF1dvPMY7jZcNNVh2gM77pw3db9JVg@mail.gmail.com>
Date:	Thu, 23 Apr 2015 09:50:17 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Denys Vlasenko <vda.linux@...glemail.com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Denys Vlasenko <dvlasenk@...hat.com>,
	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 9:41 AM, Denys Vlasenko
<vda.linux@...glemail.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

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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