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Date: Sun, 14 Aug 2011 15:29:22 +0400
From: Solar Designer <>
Cc: Chris Evans <>,
Subject: Re: 32/64 bitness restriction for pid namespace


On Sun, Aug 14, 2011 at 02:16:58PM +0400, Vasiliy Kulikov wrote:
> My current non-posted-yet patch handles the current process rather than
> a namespace.  It sets a task-related flag(s), which is checked/dropped on
> execve().  On execve() an actual locking is handled.  A locked process
> may not drop the lock.

Sounds good.

> On Sun, Aug 14, 2011 at 13:50 +0400, Solar Designer wrote:
> > So maybe the restriction should apply to a process tree rather than to a
> > namespace?
> A process tree is a horrible term.  What if some elements of fork chain
> died?

Then it's a torn tree. ;-)  OK, let's not use this term.

> > 5 - lock current process to current bitness, but execve() to 32-bit ELF
> > 6 - lock current process to current bitness, but execve() to 64-bit ELF
> > 7 - lock current process to current bitness, but next execve() to its actual bitness
> > 
> > 5 to 7 are probably not very useful, but are defined for consistency.
> These are confusing and IMO meaningless modes.

I agree.

> I think a simple way to go is an addition of PR_BITNESS_LOCK prctl() option,
> which calls __task_bitness_lock(current, current_bitness()).

I am fine with this.  I don't know which approach the LKML folks will
like best.

> Also, I try to handle syscalls as if they are not setup, but there are
> trivial ways to do something more than just 32 bit task of 32 bit kernel
> or 64 bit task of 64 bit kernel with IA32_EMULATION=n.  The obvious way
> is using CS segment of another bitness.  I bet procfs has something
> similar.  64 bit locking is rather simple as grep CONFIG_IA32_EMULATION
> shows only tens of lines (so, it can be fixed), but emulated 32 bit task
> might significantly differ from usual 32 task on 32 bit kernel.

OK, you don't have to emulate the exact same behavior.  Maybe ENOSYS
like you implemented initially would be fine.


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