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. > > [ 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. > > If performance is a concern, let's look at that in more detail. But I > don't see how the solution to a performance issue could possibly be > "leave (almost) all tasks vulnerable by default." > Thanks. Tim
