[PATCH v3 0/8] KVM: arm64: Hypervisor stack enhancements

[Kalesh Singh]

Hi all,

This is v3 of the nVHE hypervisor stack enhancements.

Previous versions can be found at:
v2: https://lore.kernel.org/r/20220222165212.2005066-1-kaleshsingh@google.com/
v1: https://lore.kernel.org/r/20220210224220.4076151-1-kaleshsingh@google.com/

The main update in this version is that the unwinder now uses the core logic
from the regular kernel stack unwinder to avoid duplicate code, per Mark; along
with fixes for the other issues identified in v2.

The previous cover letter (with updated call trace) has been copied below.

Thanks,
Kalesh

-----

This series is based on 5.17-rc5 and adds the following stack features to
the KVM nVHE hypervisor:

== Hyp Stack Guard Pages ==

Based on the technique used by arm64 VMAP_STACK to detect overflow.
i.e. the stack is aligned to twice its size which ensure that the 
'stack shift' bit of any valid SP is 0. The 'stack shift' bit can be
tested in the exception entry to detect overflow without corrupting GPRs.

== Hyp Stack Unwinder ==

Based on the arm64 kernel stack unwinder
(See: arch/arm64/kernel/stacktrace.c)

The unwinding and dumping of the hyp stack is not enabled by default and
depends on CONFIG_NVHE_EL2_DEBUG to avoid potential information leaks.

When CONFIG_NVHE_EL2_DEBUG is enabled the host stage 2 protection is
disabled, allowing the host to read the hypervisor stack pages and unwind
the stack from EL1. This allows us to print the hypervisor stacktrace
before panicking the host; as shown below.

Example call trace:

[   98.916444][  T426] kvm [426]: nVHE hyp panic at: [<ffffffc0096156fc>] __kvm_nvhe_overflow_stack+0x8/0x34!
[   98.918360][  T426] nVHE HYP call trace:
[   98.918692][  T426] kvm [426]: [<ffffffc009615aac>] __kvm_nvhe_cpu_prepare_nvhe_panic_info+0x4c/0x68
[   98.919545][  T426] kvm [426]: [<ffffffc0096159a4>] __kvm_nvhe_hyp_panic+0x2c/0xe8
[   98.920107][  T426] kvm [426]: [<ffffffc009615ad8>] __kvm_nvhe_hyp_panic_bad_stack+0x10/0x10
[   98.920665][  T426] kvm [426]: [<ffffffc009610a4c>] __kvm_nvhe___kvm_hyp_host_vector+0x24c/0x794
[   98.921292][  T426] kvm [426]: [<ffffffc009615718>] __kvm_nvhe_overflow_stack+0x24/0x34
. . .

[   98.973382][  T426] kvm [426]: [<ffffffc009615718>] __kvm_nvhe_overflow_stack+0x24/0x34
[   98.973816][  T426] kvm [426]: [<ffffffc0096152f4>] __kvm_nvhe___kvm_vcpu_run+0x38/0x438
[   98.974255][  T426] kvm [426]: [<ffffffc009616f80>] __kvm_nvhe_handle___kvm_vcpu_run+0x1c4/0x364
[   98.974719][  T426] kvm [426]: [<ffffffc009616928>] __kvm_nvhe_handle_trap+0xa8/0x130
[   98.975152][  T426] kvm [426]: [<ffffffc009610064>] __kvm_nvhe___host_exit+0x64/0x64
[   98.975588][  T426] ---- end of nVHE HYP call trace ----


Kalesh Singh (8):
  KVM: arm64: Introduce hyp_alloc_private_va_range()
  KVM: arm64: Introduce pkvm_alloc_private_va_range()
  KVM: arm64: Add guard pages for KVM nVHE hypervisor stack
  KVM: arm64: Add guard pages for pKVM (protected nVHE) hypervisor stack
  KVM: arm64: Detect and handle hypervisor stack overflows
  KVM: arm64: Add hypervisor overflow stack
  KVM: arm64: Unwind and dump nVHE HYP stacktrace
  KVM: arm64: Symbolize the nVHE HYP backtrace

 arch/arm64/include/asm/kvm_asm.h     |  20 +++
 arch/arm64/include/asm/kvm_mmu.h     |   4 +
 arch/arm64/include/asm/stacktrace.h  |  12 ++
 arch/arm64/kernel/stacktrace.c       | 210 ++++++++++++++++++++++++---
 arch/arm64/kvm/Kconfig               |   5 +-
 arch/arm64/kvm/arm.c                 |  34 ++++-
 arch/arm64/kvm/handle_exit.c         |  16 +-
 arch/arm64/kvm/hyp/include/nvhe/mm.h |   3 +-
 arch/arm64/kvm/hyp/nvhe/host.S       |  29 ++++
 arch/arm64/kvm/hyp/nvhe/hyp-main.c   |   5 +-
 arch/arm64/kvm/hyp/nvhe/mm.c         |  51 ++++---
 arch/arm64/kvm/hyp/nvhe/setup.c      |  25 +++-
 arch/arm64/kvm/hyp/nvhe/switch.c     |  30 +++-
 arch/arm64/kvm/mmu.c                 |  62 +++++---
 scripts/kallsyms.c                   |   2 +-
 15 files changed, 422 insertions(+), 86 deletions(-)


base-commit: cfb92440ee71adcc2105b0890bb01ac3cddb8507
-- 
2.35.1.473.g83b2b277ed-goog