Kernel Page Table Isolation (was KAISER) (original) (raw)

This series is a major overhaul of the KAISER patches:

  1. Entry code

Mostly the same, except for a handful of fixlets and delta
improvements folded into the corresponding patches

New: Map TSS read only into the user space visible mapping

This is 64bit only, as 32bit needs the TSS mapped RW

AMD confirmed that there is no issue with that. It would be nice to
get confirmation from Intel as well.

  1. Namespace

Several people including Linus requested to change the KAISER name.

We came up with a list of technically correct acronyms:

User Address Space Separation, prefix uass_

Forcefully Unmap Complete Kernel With Interrupt Trampolines, prefix fuckwit_

but we are politically correct people so we settled for

Kernel Page Table Isolation, prefix kpti_

Linus, your call :)

  1. The actual isolation patches

- Replaced the magic kaiser_add/remove_mapping() code by mapping everything
which needs to be shared with user space into the fixmap

- PMD aligned the shared fixmap so the PTE page can be shared between
user and kernel space page tables

- Integrated all fixes and Peters rewrite of the PCID/TLB flush code.

- Restructured the patch set in a way that it is simpler to review

- Got rid of the strange wording of shadow page tables, because they are
not shadowish at all. KASAN, virt etc. use shadows, but these tables
are actively in use and integral part of the functionality

- Moved the debugfs files into a new directory so they don't clutter the
debugfs root directory.

LIMITATIONS:

- allmod/yes config builds fail right now because the fixmap grows
too large and breaks the EFI assumptions. This is still investigated.

A possible solution is just to use one of the address space holes
and grab a separate pgdir to map the cpu entry area. Not hard to do
and it wont change much of the principle of these patches.

TODOs:

- This needs a thorough review again. Sorry.

- Please verify that all fixlets have been integrated. The mail threads
are horribly scattered so I might have missed something.

- Rewrite documentation. I dropped the documentation patch as it not
longer applies.

- Handle native vsyscalls. Right now the patch set supports only
emulation, but it should be possible to support native as well.
Nothing urgent, I'd rather prefer to kill them completely.

- Populate a branch with minimal prerequisite patches to apply.

Thanks to Andy Lutomirsky, Peter Zijlstra, Ingo Molnar, Borislav Petkov and
Dave Hansen for all the help with this.

The patches apply on top of

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/urgent

and are available from git in

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git WIP.x86/kpti

and as tarball from

https://tglx.de/~tglx/patches-kpti-119.tar.bz2

Signature file for the uncompressed tarball

https://tglx.de/~tglx/patches-kpti-119.tar.sig

Thanks,

tglx