Re: [PATCH] mm: Add new vma flag VM_LOCAL_CPU

From: Matthew Wilcox
Date: Tue May 15 2018 - 13:37:45 EST

On Tue, May 15, 2018 at 02:41:41PM +0300, Boaz Harrosh wrote:
> That would be very hard. Because that program would:
> - need to be root
> - need to start and pretend it is zus Server with the all mount
> thread thing, register new filesystem, grab some pmem devices.
> - Mount the said filesystem on said pmem. Create core-pinned ZT threads
> for all CPUs, start accepting IO.
> - And only then it can start leaking the pointer and do bad things.

All of these things you've done for me by writing zus Server. All I
have to do now is compromise zus Server.

> The bad things it can do to the application, not to the Kernel.
> And as a full filesystem it can do those bad things to the application
> through the front door directly not needing the mismatch tlb at all.

That's not true. When I have a TLB entry that points to a page of kernel
ram, I can do almost anything, depending on what the kernel decides to
do with that ram next. Maybe it's page cache again, in which case I can
affect whatever application happens to get it allocated. Maybe it's a
kmalloc page next, in which case I can affect any part of the kernel.
Maybe it's a page table, then I can affect any process.

> That said. It brings up a very important point that I wanted to talk about.
> In this design the zuf(Kernel) and the zus(um Server) are part of the distribution.
> I would like to have the zus module be signed by the distro's Kernel's key and
> checked on loadtime. I know there is an effort by Redhat guys to try and sign all
> /sbin/* servers and have Kernel check these. So this is not the first time people
> have thought about that.

You're getting dangerously close to admitting that the entire point
of this exercise is so that you can link non-GPL NetApp code into the
kernel in clear violation of the GPL.