Re: some possible fixes in the OE web pages

[Martin Jansa <martin.jansa@gmail.com>]

On Thu, May 13, 2010 at 12:23:22PM +0400, Roman I Khimov wrote:
> В сообщении от Четверг 13 мая 2010 10:40:37 автор Martin Jansa написал:
> > On Thu, May 13, 2010 at 09:53:54AM +0400, Roman I Khimov wrote:
> > > В сообщении от Четверг 13 мая 2010 01:30:53 автор Robert P. J. Day 
> написал:
> > > > * on http://wiki.openembedded.net/index.php/OEandYourDistro#Ubuntu,
> > > > there's a reference to configuring for qemu-arm:
> > > >
> > > >   echo 128 > /proc/sys/vm/mmap_min_addr
> > > >
> > > > from memory, i always simply set that to zero on fedora.  is there
> > > > something magic about the value 128?  at the moment, it's at the
> > > > default value of 65536 on this ubuntu system.
> > >
> > > With current qemu in OE mmap_min_addr tricks are not needed at all.
> > 
> > On some systems (I have report from fedora and kubuntu) it still needs 0
> > in mmap_min_addr :/.
> > 
> > Investigating why, but it's slow because it doesn't fail on my box.
> > 
> > My guess is that this chunk from
> > http://git.qemu.org/qemu.git/tree/linux-user/main.c
> > cannot work on systems where normal user is not allowed to read
> > /proc/sys/vm/mmap_min_addr and mmap_min_addr is not initialized with
> > sane value.
> 
> Just checked with Ubuntu and Fedora, it really isn't possible to read 
> /proc/sys/vm/mmap_min_addr as regular user, although it has 644 permissions on 
> it. "Security"? Damn.
> 
> [after 15 minutes]
> 
> OK, actually there is a useful entry on Launchpad:
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/568844
> 
> The real solution is in the kernel, it should be fixed for latest Ubuntu and 
> hopefully Fedora will catch up on this issue too.
> 
> http://git.kernel.org/?p=linux/kernel/git/jmorris/security-
> testing-2.6.git;a=commitdiff;h=822cceec7248013821d655545ea45d1c6a9d15b3
> 
> Interesting that openSUSE with 2.6.31 kernel doesn't have such problems... And 
> our main build machine with Debian stable + 2.6.30 kernel works fine too. 
> Probably this check got introduced in 2.6.32.

Hi,

tt was introduced somewhere in 2.6.33-rc[12]
http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=0e1a6ef2dea88101b056b6d9984f3325c5efced3
see my commit:
http://git.openembedded.org/cgit.cgi/openembedded/commit/?id=1b426b8382d2a7864b63051b0707e577f2c0ce69

but really strange thing is:
bitbake@jama ~/build.dev.shr.gta $ cat /proc/sys/vm/mmap_min_addr
cat: /proc/sys/vm/mmap_min_addr: Operation not permitted
root@jama series # cat /proc/sys/vm/mmap_min_addr
4096
Linux jama 2.6.34-rc7-JaMa-00056-gcea0d76 #7 SMP PREEMPT

and qemu-native/kqemu still works (probably simple cat is not good
test, maybe qemu-arm gets higher capabilities before trying to read it
and it's enough on my box and not enough somewhere else).

> Well, as the problem is in the kernel really, I think everyone having this 
> problem should push distro maintainers to update kernels with the tiny fix 
> mentioned above. But as a workaround, yep, "0" setting might work (beware that 
> it might also not work as in here:
> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/423513
> ).

Another not tested workaround:

as qemu can work with (hopefully any) non-zero mmap_min_addr, maybe add
patch to linux-user/main.c that if it cannot read
/proc/sys/vm/mmap_min_addr then assume 65536 (ubuntu default)?

Regards,

> 
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Jansa Martin                 sip:jamasip@voip.wengo.fr 
JaMa