CVE-2026-53199

In the Linux kernel, the following vulnerability has been resolved:

hvnetvsc: use kmaplocalpage in netvsccopytosend_buf

netvsccopytosendbuf() copies page buffer entries into the VMBus send buffer using phystovirt() on the entry PFN. Entries for the RNDIS header and the skb linear data come from kmalloc'd memory and are always in the kernel direct map, but entries for skb fragments reference page cache or user pages, which on 32-bit x86 with CONFIGHIGHMEM=y can live above the LOWMEM boundary. For such a page physto_virt() returns an address outside the direct map and the subsequent memcpy() faults on the transmit softirq path, which is fatal.

Map the pages with kmaplocalpage() instead, handling two properties of the page buffer entries:

• pb[i].pfn is a Hyper-V PFN at HVHYPPAGESIZE (4K) granularity, not a native PFN. Reconstruct the physical address first and derive the native page from it, so the mapping stays correct where PAGESIZE > HVHYPPAGE_SIZE (e.g. arm64 with 64K pages).

• Since commit 41a6328b2c55 ("hvnetvsc: Preserve contiguous PFN grouping in the page buffer array"), an entry describes a full physically contiguous fragment and pb[i].len can exceed PAGESIZE, while kmaplocalpage() maps a single page. Copy page by page, splitting at native page boundaries.

The copy path only handles packets smaller than the send section size (6144 bytes by default); larger packets take the cppartial path where only the RNDIS header is copied. So entries here are bounded by the section size and a copy is split at most once on 4K-page systems. On !CONFIGHIGHMEM configs kmaplocalpage() folds to page_address() and no mapping work is added.