[PATCH 2/2] arm/arm64: KVM: Ensure memslots are within KVM_PHYS_SIZE

On Tue, Sep 30, 2014 at 01:46:51PM +0100, Catalin Marinas wrote:

On Thu, Sep 25, 2014 at 08:42:54PM +0100, Christoffer Dall wrote:

quoted

When creating or moving a memslot, make sure the IPA space is within the
addressable range of the guest.  Otherwise, user space can create too
large a memslot and KVM would try to access potentially unallocated page
table entries when inserting entries in the Stage-2 page tables.

Signed-off-by: Christoffer Dall <redacted>
---
 arch/arm/kvm/mmu.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index 4532f5f..52a311a 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c

@@ -975,6 +975,9 @@ int kvm_handle_guest_abort(struct kvm_vcpu *vcpu, struct kvm_run *run)
 		goto out_unlock;
 	}
 
+	/* Userspace should not be able to register out-of-bounds IPAs */

I think "userspace" is a bit misleading (should be "guests").

see below

quoted

+	VM_BUG_ON(fault_ipa >= KVM_PHYS_SIZE);

Can guests not generate IPA addresses higher than KVM_PHYS_SIZE? I don't
see why this wouldn't be possible when PARange > 40.

Guests can, but higher in this function we resolve the the gfn (IPA) to
a memslot (hva).  That only succeeds if userspace actually managed to
register a memslot with such an IPA, which we prevent in the other part
of this patch.  So if we get here, it's a bug, because we should have
entered the section above and taken the goto out_unlock.

Makes sense?

Thanks,
-Christoffer