On Tue, Jan 30, 2018 at 01:23:17PM -0800, Tim Chen wrote: > On 01/30/2018 09:48 AM, Josh Poimboeuf wrote: > > On Mon, Jan 29, 2018 at 10:04:47PM +0000, David Woodhouse wrote: > >> From: Tim Chen <tim.c.c...@linux.intel.com> > >> > >> Flush indirect branches when switching into a process that marked itself > >> non dumpable. This protects high value processes like gpg better, > >> without having too high performance overhead. > > > > I wonder what the point of this patch is. An audit of my laptop shows > > only a single user of PR_SET_DUMPABLE: systemd-coredump. > > This is an opt in approach. For processes who need extra > security, it set itself as non-dumpable. Then it can > ensure that it doesn't see any poisoned BTB.
I don't want other users reading my applications' memory. I don't want other containers reading my containers' memory. I don't want *any* user tasks reading root daemons' memory. Those are not unreasonable expectations. So now I have to go and modify all my containers and applications to set PR_SET_DUMPABLE? That seems highly impractical and unlikely. Plus, I happen to *like* core dumps. The other option is to rebuild the entire userland with retpolines, but again, that would make this patch completely pointless. > > [ And yes, I have gpg-agent running. Also, a grep of the gnupg source > > doesn't show any evidence of it being used there. So the gpg thing > > seems to be a myth. ] > > I'm less familiar with gpg-agent. Dave was the one who > put in comments about gpg-agent in this patch so perhaps > he can comment. > > > > > But also, I much preferred the original version of the patch which only > > skipped IBPB when 'prev' could ptrace 'next'. > > For the A->kernel thread->B scenario, you will need context of A > to decide if you need IBPB when switching to B. You need to > worry about whether the context of A has been released ... etc if > you want to use ptrace. Is that why the ptrace approach was abandoned? Surely that's a solvable problem? We have some smart people on lkml. And anyway I didn't see it discussed anywhere. In the worst case we could just always do IBPB when switching between kernel and user tasks. -- Josh
