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

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Message-ID: <20150423171440.GP28327@pd.tnic>
Date:	Thu, 23 Apr 2015 19:14:40 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Denys Vlasenko <vda.linux@...glemail.com>,
	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 09:50:17AM -0700, Andy Lutomirski wrote:
> 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

[  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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