Checkpoint: what has actually crossed the boundary?

Download More RAM becomes clearer when its first four technical moves are treated as one change in authority rather than as a list of tricks. The question here is what the paper has established by the time it can read a decoded physical-memory view, and what still separates that disclosure from reliable control. The answer gives a useful judgment: the attack has already crossed the VBS confidentiality boundary, but the full system-compromise claim depends on a further escalation through a fragile write and code-integrity authority.

One physical region, two descriptions

The intended VBS model has a clean order of responsibility. Hardware and firmware provide a memory map. Windows uses that map to build virtual memory and allocate pages. Hyper-V separates the ordinary Windows environment in VTL0 from VTL1, where the Secure Kernel and Isolated User Mode handle security-sensitive work. HVCI then relies on that protected side to validate drivers and enforce memory-integrity rules. Each layer can be doing its local job correctly because each one receives an address and a policy from the layer below.

Download More RAM does not initially ask the Secure Kernel to approve bad code. It changes the object that all of those decisions refer to. The lower half of the reported physical range and the upper half are different address values in Windows’ bookkeeping, yet the DIMM’s row decoder sends both toward the same storage cells. The operating system has two entries; the hardware has one destination. That is why calling the result a “VBS escape” can be misleading if it suggests a program simply jumped from VTL0 into VTL1. The first failure is earlier: the meaning of a physical address is no longer unique.

This distinction also explains why page permissions alone cannot settle the issue. A page table can say that one physical page is unavailable or that a code page is not writable. HVCI can enforce a write-or-execute policy over the pages it knows about. But those rules are indexed by the map that Windows and the hypervisor were given. If another physical address reaches the same cells, the lower layer has created a second route without requiring the higher layer to misclassify the original page.

The attack can therefore be understood as a disagreement between two maps:

• The policy map is the one Windows and VBS use to decide which ranges exist, which pages are allocated, and which security domain owns them.
• The hardware map is the one the memory controller applies when it turns address bits into rows, columns, and cells.
• In the normal system, the two maps are assumed to agree.
• Under the demonstrated alias, the policy map contains two regions while the hardware map collapses them onto one.

That disagreement does not make every operation succeed. In fact, ordinary operation becomes dangerous because Windows continues to trust the policy map while the controller follows the hardware map. A normal allocation in the upper range can overwrite lower-half state. A request aimed at a supposedly unused address can damage a live kernel object.