BTI interaction between seccomp filters in systemd and glibc mprotect calls, causing service failures

[Jordan Glover]

On Saturday, October 24, 2020 2:12 PM, Salvatore Mesoraca <s.mesoraca16 at gmail.com> wrote:

> On Sat, 24 Oct 2020 at 12:34, Topi Miettinen toiwoton at gmail.com wrote:
>
> > On 23.10.2020 20.52, Salvatore Mesoraca wrote:
> >
> > > Hi,
> > > On Thu, 22 Oct 2020 at 23:24, Topi Miettinen toiwoton at gmail.com wrote:
> > >
> > > > SARA looks interesting. What is missing is a prctl() to enable all W^X
> > > > protections irrevocably for the current process, then systemd could
> > > > enable it for services with MemoryDenyWriteExecute=yes.
> > >
> > > SARA actually has a procattr[0] interface to do just that.
> > > There is also a library[1] to help using it.
> >
> > That means that /proc has to be available and writable at that point, so
> > setting up procattrs has to be done before mount namespaces are set up.
> > In general, it would be nice for sandboxing facilities in kernel if
> > there would be a way to start enforcing restrictions only at next
> > execve(), like setexeccon() for SELinux and aa_change_onexec() for
> > AppArmor. Otherwise the exact order of setting up various sandboxing
> > options can be very tricky to arrange correctly, since each option may
> > have a subtle effect to the sandboxing features enabled later. In case
> > of SARA, the operations done between shuffling the mount namespace and
> > before execve() shouldn't be affected so it isn't important. Even if it
> > did (a new sandboxing feature in the future would need trampolines or
> > JIT code generation), maybe the procattr file could be opened early but
> > it could be written closer to execve().
>
> A new "apply on exec" procattr file seems reasonable and relatively easy to add.
> As Kees pointed out, the main obstacle here is the fact that SARA is
> not upstream :(
>
> Salvatore

Is there a chance we will see new SARA iteration soon on lkml? :)

Jordan