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

[Kalesh Singh]

On Wed, Feb 23, 2022 at 9:15 PM Kalesh Singh <kaleshsingh at google.com> wrote:
>
> Hi all,
>
> This is v3 of the nVHE hypervisor stack enhancements.

Please find the latest version v4, posted at:
https://lore.kernel.org/r/20220225033548.1912117-1-kaleshsingh@google.com/

Thanks,
Kalesh

>
> 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
>