linux-kernel - Re: [3.1 patch] x86: default to vsyscall=native

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Message-ID: <20111005223055.GG14406@localhost.pp.htv.fi>
Date:	Thu, 6 Oct 2011 01:30:57 +0300
From:	Adrian Bunk <bunk@...sta.de>
To:	richard -rw- weinberger <richard.weinberger@...il.com>
Cc:	Andrew Lutomirski <luto@....edu>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [3.1 patch] x86: default to vsyscall=native

On Thu, Oct 06, 2011 at 12:22:34AM +0200, richard -rw- weinberger wrote:
> On Thu, Oct 6, 2011 at 12:13 AM, Andrew Lutomirski <luto@....edu> wrote:
> > On Mon, Oct 3, 2011 at 10:33 AM, Adrian Bunk <bunk@...sta.de> wrote:
> >> On Mon, Oct 03, 2011 at 06:04:53AM -0700, Andrew Lutomirski wrote:
> >>> On Mon, Oct 3, 2011 at 2:08 AM, Adrian Bunk <bunk@...sta.de> wrote:
> >>> > After upgrading a kernel the existing userspace should just work
> >>> > (assuming it did work before ;-) ), but when I upgraded my kernel
> >>> > from 3.0.4 to 3.1.0-rc8 a UML instance didn't come up properly.
> >>> >
> >>> > dmesg said:
> >>> >  linux-2.6.30.1[3800] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb9c498 ax:ffffffffff600000 si:0 di:606790
> >>> >  linux-2.6.30.1[3856] vsyscall fault (exploit attempt?) ip:ffffffffff600000 cs:33 sp:7fbfb13168 ax:ffffffffff600000 si:0 di:606790
> >>> >
> >>> > Looking throught the changelog I ended up at commit 3ae36655
> >>> > ("x86-64: Rework vsyscall emulation and add vsyscall= parameter").
> >>> >
> >>> > Linus suggested in https://lkml.org/lkml/2011/8/9/376 to default to
> >>> > vsyscall=native.
> >>> >
> >>> > That sounds reasonable to me, and fixes the problem for me.
> >>>
> >>> At this point in the -rc cycle, this sounds fine.
> >>>
> >>> That being said, I'd like to fix it for real for 3.2.  This particular
> >>> failure is suspicious -- the "vsyscall fault" message means that
> >>> sys_gettimeofday returned EFAULT, which means that the old (3.0 and
> >>> before) vgettimeofday should *also* have segfaulted.
> >>
> >> This 2.6.30.1 UML kernel binary from 2009 worked for me for all host
> >> kernels from 2.6.30 to 3.0, and with 3.1.0-rc8 and vsyscall=native
> >> it also seems to run nicely.
> >>
> >> Looking deeper into "a UML instance didn't come up properly",
> >> the problem is that it comes up in a strange (readonly) state.
> >>
> >> There are "Using makefile-style concurrent boot in runlevel S."
> >> and "Using makefile-style concurrent boot in runlevel 2." in the
> >> logs with a Debian userspace, but no output from the init scripts
> >> in these broken bootups (normal messages are in non-broken bootups).
> >>
> >> Perhaps the two the messages I see in dmesg on the host are from the
> >> processes running rcS and rc2 failing early?
> >>
> >> In a working startup with a Debian userspace, I'm getting during rcS
> >>  Setting the system clock.
> >>  Cannot access the Hardware Clock via any known method.
> >>  Use the --debug option to see the details of our search for an access method.
> >>  Unable to set System Clock to: Mon Oct 3 17:01:35 UTC 2011 ... (warning).
> >>
> >>> We do have a bit
> >>> of a bug in that the new code doesn't report si_addr properly, but
> >>> that sounds unlikely as a culprit.  Did you try with the offending
> >>> commit reverted (i.e. fce8dc0)?  I bet that it also fails there.
> >>
> >> fce8dc0 is "x86-64: Wire up getcpu syscall", is that really the one you
> >> want me to revert?
> >>
> >>> What's the .config for your UML binary?  I'd like to see if I can
> >>> reproduce this.
> >>
> >> It's attached.
> >>
> >
> > I can't reproduce it.  What distro is running inside the UML instance?
> 
> Same here.
> Adrian, is the UML kernel crashing before executing init?

As I wrote:
  Looking deeper into "a UML instance didn't come up properly",
  the problem is that it comes up in a strange (readonly) state.

The UML kernel is running happily without crashing, and as I wrote my
guess about my problems is:
  Perhaps the two the messages I see in dmesg on the host are from the
  processes running rcS and rc2 failing early?

> We definitely need more information...

I gave the information that was requested. plus my observations.

What more information exactly do you need from me?

> Thanks,
> //richard

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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