Re: RELEASE BLOCKER: Linux doesn't follow x86/x86-64 ABI wrt direction flag

Joe Buck
2008-03-06T17:59:01Z

On Thu, Mar 06, 2008 at 03:12:21PM +0100, Olivier Galibert wrote:
> On Thu, Mar 06, 2008 at 03:03:15PM +0100, Paolo Bonzini wrote:
> > Olivier Galibert wrote:
> > >On Wed, Mar 05, 2008 at 05:12:07PM -0800, H. Peter Anvin wrote:
> > >>It's a kernel bug, and it needs to be fixed.
> > >
> > >I'm not convinced. It's been that way for 15 years, it's that way in
> > >the BSD kernels, at that point it's a feature. The bug is in the
> > >documentation, nowhere else. And in gcc for blindly trusting the
> > >documentation.
> >
> > No, the bug *in the kernel* was already present (if you had a signal
> > raised during a call to memmove). It's just more visible with GCC 4.3.
>
> I'm curious, since when paper documentation became the Truth and
> reality became a bug?

If the kernel allows state to leak from one process to another,
for example from a process running as root to a process running as an
ordinary user, it's a bug, with possible security implications.

In this particular case not much can be communicated through a one-bit
flag, so it would only be relevant in those situations where you want
to forbid any communication channels from a given process. So the
kernel developers might consider it a trivial bug. Or, they could just
fix it, which I understand is the plan.