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

From: Ard Biesheuvel
Date: Fri Sep 22 2017 - 17:44:58 EST

On 25 August 2017 at 01:31, Florent Revest <florent.revest@xxxxxxx> 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.
> 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

Hello Florent,

This is really nice work. Thanks for contributing it.

>From the EFI side, there are some minor concerns on my part regarding
the calling convention, and the fact that we can no longer invoke
runtime services from a kernel running at EL1, but those all seem
fixable. I will respond to the patches in question in greater detail
at a later time.

In the mean time, Christoffer has raised a number for valid concerns,
and those need to be addressed first before it makes sense to talk
about EFI specifics. I hope you will find more time to invest in this:
I would really love to have this feature upstream.