[v2,0/4] Fix some KVM/HYP interactions with kprobes
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Message ID 20190124163257.233929-1-james.morse@arm.com
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  • Fix some KVM/HYP interactions with kprobes
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James Morse Jan. 24, 2019, 4:32 p.m. UTC
Hi guys,

When looking at Masami Hiramatsu's kprobe cleanup series, it occurred
to me the 'no KVM' isn't just about the EL1/EL2  split on non-VHE systems,
but whether KVM is prepared to handle stepping on a breakpoint. It's not.

This labels all the VHE-only KVM functions that run during world switch
with NOKPROBE_SYMBOL(), and always blacklists __hyp_text for kprobes
to cover the common guest entry/exit code.

I anticipate patch 1 going via the KVM tree to avoid conflicts.
Patch 2 will conflict with [0].


I'm not sure what the best thing to do with the hyp-stub is.
Patch 3 moves it to __hyp_text, and patch 4 covers the hibernate fallout
from doing that. We don't have any other mmu-off but not idmap'd text.
Probing the hyp-stub has to be done by address as the symbol names
alias those in the __entry_text, which is blacklisted. (although this
might depend on link order). I think anyone doing this is trying to
shoot themselves in the foot.


Know issues:
* Other regions we should blacklist are the kexec and hibernate 'copy
  everything' code, as the vectors may have been overwritten by the time
  we step on the probe. cpu-suspend needs investigating...


Thanks,

James

[0] lore.kernel.org/r/154753341900.31541.8135985235882849464.stgit@devbox

James Morse (4):
  KVM: arm64: Forbid kprobing of the VHE world-switch code
  arm64: kprobe: Always blacklist the KVM world-switch code
  arm64: hyp-stub: Forbid kprobing of the hyp-stub
  arm64: hibernate: Clean the __hyp_text to PoC after resume

 arch/arm64/kernel/hibernate.c      | 4 +++-
 arch/arm64/kernel/hyp-stub.S       | 2 ++
 arch/arm64/kernel/probes/kprobes.c | 6 +++---
 arch/arm64/kvm/hyp/switch.c        | 5 +++++
 arch/arm64/kvm/hyp/sysreg-sr.c     | 5 +++++
 5 files changed, 18 insertions(+), 4 deletions(-)