Re: [PATCH v5 5/6] KVM: guest_memfd: Establish memslot<=>guest_memfd bindings *after* memslot is ready

[Ackerley Tng]

Sean Christopherson <seanjc@xxxxxxxxxx> writes:

> Wait to bind a memslot to a guest_memfd instance until *after* the memslot
> is fully prepared, as creating the binding in guest_memfd will effectively
> expose the memslot to readers.  As pointed out by Sashiko, binding the
> memslot before it's ready to be exposed to the rest of the world can break
> various memslot assumption and rules.  E.g. x86 could observe a NULL rmap
> pointer if a PUNCH_HOLE hit the guest_memfd after the binding was created,
> but before KVM made it through kvm_prepare_memory_region().
>
> Fixes: a7800aa80ea4 ("KVM: Add KVM_CREATE_GUEST_MEMFD ioctl() for guest-specific backing memory")
> Cc: stable@xxxxxxxxxxxxxxx
> Reported-by: Sashiko Bot <sashiko-bot@xxxxxxxxxx>
> Closes: https://lore.kernel.org/all/20260826170551.BEF801F000E9@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Hope you consider my suggestion on [4/6]. Either way,

Reviewed-by: Ackerley Tng <ackerleytng@xxxxxxxxxx>