Messages in this thread | | | Subject | Re: [PATCH] x86/speculation: Use Indirect Branch Prediction Barrier in context switch | From | Tim Chen <> | Date | Tue, 30 Jan 2018 13:23:17 -0800 |
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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.chen@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
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