Re: [RFC 00/11] KVM, EFI, arm64: EFI Runtime Services Sandboxing

[Christoffer Dall]

Hi Florent,

On Fri, Aug 25, 2017 at 09:31:30AM +0100, Florent Revest wrote:
> Hi,
> 
> This series implements a mechanism to sandbox EFI Runtime Services on arm64.
> It can be enabled with CONFIG_EFI_SANDBOX. At boot it spawns an internal KVM
> virtual machine that is ran everytime an EFI Runtime Service is called. This
> limits the possible security and stability impact of EFI runtime on the kernel.

I wonder if this should be split into two series; one that sets up
anything you may need from KVM, and another one that uses that for UEFI.

There's a lot KVM and UEFI intertwined logic and assumptions in patch
10, which makes this series a bit hard to read.

I'd like some documentation (in the series and in
Documentation/virtual/kvm) of how this works, and which hidden
assumptions there are.  For example, how do you ensure you never attempt
to return to userspace?  How many VCPUs do you support?  Do you support
any form of virtual interrupts?  How about timers?  Can a VM access
physical devices?  How do you debug and trace something like this?  Can
the VM be monitored from userspace?

These feel like fundamental questions to me that needs addressing before
I can competently review the code.

I think a slightly more concrete motivation and outlining the example of
the broken UEFI on Seattle would help paving the way for these patches.


Thanks,
-Christoffer

> 
> The patch set is split as follow:
>  - Patches 1 and 2: Give more control over HVC handling to KVM
>  - Patches 3 to 6: Introduce the concept of KVM "internal VMs"
>  - Patches 7 to 9: Reorder KVM and EFI initialization on ARM
>  - Patch 10: Introduces the EFI sandboxing VM and wrappers
>  - Patch 11: Workarounds some EFI Runtime Services relying on EL3
> 
> The sandboxing has been tested to work reliably (rtc and efivars) on a
> SoftIron OverDrive 1000 box and on a ARMv8.3 model with VHE enabled. Normal
> userspace KVM instance have also been tested to still work correctly.
> 
> Those patches apply cleanly on the Linus' v4.13-rc6 tag and have no other
> dependencies.
> 
> Florent Revest (11):
>   arm64: Add an SMCCC function IDs header
>   KVM: arm64: Return an Unknown ID on unhandled HVC
>   KVM: Allow VM lifecycle management without userspace
>   KVM, arm, arm64: Offer PAs to IPAs idmapping to internal VMs
>   KVM: Expose VM/VCPU creation functions
>   KVM, arm64: Expose a VCPU initialization function
>   KVM: Allow initialization before the module target
>   KVM, arm, arm64: Initialize KVM's core earlier
>   EFI, arm, arm64: Enable EFI Runtime Services later
>   efi, arm64: Sandbox Runtime Services in a VM
>   KVM, arm64: Don't trap internal VMs SMC calls
> 
>  arch/arm/include/asm/efi.h                 |   7 +
>  arch/arm/include/asm/kvm_coproc.h          |   3 +
>  arch/arm/include/asm/kvm_host.h            |   1 +
>  arch/arm/include/asm/kvm_psci.h            |   1 +
>  arch/arm/kvm/coproc.c                      |   6 +
>  arch/arm/kvm/coproc_a15.c                  |   3 +-
>  arch/arm/kvm/coproc_a7.c                   |   3 +-
>  arch/arm64/include/asm/efi.h               |  71 ++++
>  arch/arm64/include/asm/kvm_emulate.h       |   3 +
>  arch/arm64/include/asm/kvm_host.h          |   4 +
>  arch/arm64/include/asm/kvm_psci.h          |   1 +
>  arch/arm64/kernel/asm-offsets.c            |   3 +
>  arch/arm64/kvm/handle_exit.c               |  27 +-
>  arch/arm64/kvm/sys_regs_generic_v8.c       |   8 +-
>  arch/x86/include/asm/efi.h                 |   2 +
>  drivers/firmware/efi/Kconfig               |  10 +
>  drivers/firmware/efi/Makefile              |   1 +
>  drivers/firmware/efi/arm-runtime.c         |   5 +-
>  drivers/firmware/efi/arm-sandbox-payload.S |  96 +++++
>  drivers/firmware/efi/arm-sandbox.c         | 569 +++++++++++++++++++++++++++++
>  drivers/firmware/efi/efi.c                 |   3 +
>  include/linux/kvm_host.h                   |   4 +
>  include/linux/smccc_fn.h                   |  53 +++
>  include/uapi/linux/psci.h                  |   2 +
>  virt/kvm/arm/arm.c                         |  18 +-
>  virt/kvm/arm/mmu.c                         |  76 +++-
>  virt/kvm/arm/psci.c                        |  21 ++
>  virt/kvm/kvm_main.c                        | 102 ++++--
>  28 files changed, 1050 insertions(+), 53 deletions(-)
>  create mode 100644 drivers/firmware/efi/arm-sandbox-payload.S
>  create mode 100644 drivers/firmware/efi/arm-sandbox.c
>  create mode 100644 include/linux/smccc_fn.h
> 
> --
> 1.9.1
> 
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