Re: [PATCH] mm: optionally disable brk()

[Topi Miettinen]

On 5.10.2020 15.25, David Laight wrote:
> From: David Hildenbrand
> > Sent: 05 October 2020 13:19
> >
> > On 05.10.20 13:21, David Laight wrote:
> > > From: David Hildenbrand
> > > > Sent: 05 October 2020 10:55
> > > ...
> > > > > If hardening and compatibility are seen as tradeoffs, perhaps there
> > > > > could be a top level config choice (CONFIG_HARDENING_TRADEOFF) for this.
> > > > > It would have options
> > > > > - "compatibility" (default) to gear questions for maximum compatibility,
> > > > > deselecting any hardening options which reduce compatibility
> > > > > - "hardening" to gear questions for maximum hardening, deselecting any
> > > > > compatibility options which reduce hardening
> > > > > - "none/manual": ask all questions like before
> > > >
> > > > I think the general direction is to avoid an exploding set of config
> > > > options. So if there isn't a *real* demand, I guess gluing this to a
> > > > single option ("CONFIG_SECURITY_HARDENING") might be good enough.
> > >
> > > Wouldn't that be better achieved by run-time clobbering
> > > of the syscall vectors?
> >
> > You mean via something like a boot parameter? Possibly yes.
>
> I was thinking of later.
> Some kind of restricted system might want the 'clobber'
> mount() after everything is running.

Perhaps suitably privileged tasks should be able to install global 
seccomp filters which would disregard any NoNewPrivileges requirements 
and would apply immediately to all tasks. The boot parameter would be 
also nice so that initrd and PID1 would be also restricted. Seccomp 
would also allow more specific filtering than messing with the syscall 
tables.

-Topi