[0/3] kvm: arm64: Pointer Authentication handling fixes

Message

Marc Zyngier June 4, 2020, 1:33 p.m. UTC

I recently discovered that the Pointer Authentication (PtrAuth)
handling code in KVM is busted, and has been for a while. The main
issue is that the we save the host's keys from a preemptible
context. Things will go wrong at some point.

In order to address this, the first patch move the saving of the
host's keys to vcpu_load(). It is done eagerly, which is a bore, but
is at least safe. This is definitely stable material.

The following two patches are adding an optimisation and a fix for a
corner case: we handle key saving and HCR massaging as a fixup, much
like the FPSIMD code. This subsequently allows us to deal with the
ugly case of a guest enabling PtrAuth despite it not being advertised,
resulting in PAC instructions UNDEF'ing while they should be NOPs.

This has been very lightly tested on a model.

Marc Zyngier (3):
  KVM: arm64: Save the host's PtrAuth keys in non-preemptible context
  KVM: arm64: Handle PtrAuth traps early
  KVM: arm64: Enforce PtrAuth being disabled if not advertized

 arch/arm64/include/asm/kvm_emulate.h |  6 ---
 arch/arm64/kvm/arm.c                 |  3 +-
 arch/arm64/kvm/handle_exit.c         | 38 ---------------
 arch/arm64/kvm/hyp/switch.c          | 73 ++++++++++++++++++++++++++++
 arch/arm64/kvm/sys_regs.c            | 13 ++---
 5 files changed, 80 insertions(+), 53 deletions(-)