On 30.10.24 14:49, Patrick Roy wrote:
Unmapping virtual machine guest memory from the host kernel's direct map
is a successful mitigation against Spectre-style transient execution
issues: If the kernel page tables do not contain entries pointing to
guest memory, then any attempted speculative read through the direct map
will necessarily be blocked by the MMU before any observable
microarchitectural side-effects happen. This means that Spectre-gadgets
and similar cannot be used to target virtual machine memory. Roughly 60%
of speculative execution issues fall into this category [1, Table 1].
This patch series extends guest_memfd with the ability to remove its
memory from the host kernel's direct map, to be able to attain the above
protection for KVM guests running inside guest_memfd.
=== Changes to v2 ===
- Handle direct map removal for physically contiguous pages in arch code
(Mike R.)
- Track the direct map state in guest_memfd itself instead of at the
folio level, to prepare for huge pages support (Sean C.)
- Allow configuring direct map state of not-yet faulted in memory
(Vishal A.)
- Pay attention to alignment in ftrace structs (Steven R.)
Most significantly, I've reduced the patch series to focus only on
direct map removal for guest_memfd for now, leaving the whole "how to do
non-CoCo VMs in guest_memfd" for later. If this separation is
acceptable, then I think I can drop the RFC tag in the next revision
(I've mainly kept it here because I'm not entirely sure what to do with
patches 3 and 4).
Hi,
keeping upcoming "shared and private memory in guest_memfd" in mind, I
assume the focus would be to only remove the direct map for private memory?
So in the current upstream state, you would only be removing the direct
map for private memory, currently translating to "encrypted"/"protected"
memory that is inaccessible either way already.
Correct?
--
Cheers,
David / dhildenb
