CVE-2026-43348: mshv_vtl: Fix vmemmap_shift exceeding MAX_FOLIO_ORDER

CVE-2026-43348: mshv_vtl: Fix vmemmap_shift exceeding MAX_FOLIO_ORDER

[Greg Kroah-Hartman]

From: Greg Kroah-Hartman <gregkh@kernel.org>

Description
===========

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

mshv_vtl: Fix vmemmap_shift exceeding MAX_FOLIO_ORDER

When registering VTL0 memory via MSHV_ADD_VTL0_MEMORY, the kernel
computes pgmap->vmemmap_shift as the number of trailing zeros in the
OR of start_pfn and last_pfn, intending to use the largest compound
page order both endpoints are aligned to.

However, this value is not clamped to MAX_FOLIO_ORDER, so a
sufficiently aligned range (e.g. physical range
[0x800000000000, 0x800080000000), corresponding to start_pfn=0x800000000
with 35 trailing zeros) can produce a shift larger than what
memremap_pages() accepts, triggering a WARN and returning -EINVAL:

  WARNING: ... memremap_pages+0x512/0x650
  requested folio size unsupported

The MAX_FOLIO_ORDER check was added by
commit 646b67d57589 ("mm/memremap: reject unreasonable folio/compound
page sizes in memremap_pages()").

Fix this by clamping vmemmap_shift to MAX_FOLIO_ORDER so we always
request the largest order the kernel supports, in those cases, rather
than an out-of-range value.

Also fix the error path to propagate the actual error code from
devm_memremap_pages() instead of hard-coding -EFAULT, which was
masking the real -EINVAL return.

The Linux kernel CVE team has assigned CVE-2026-43348 to this issue.


Affected and fixed versions
===========================

	Issue introduced in 6.19 with commit 7bfe3b8ea6e30437e01fcb8e4f56ef6e4d986d0f and fixed in 7.0.2 with commit a142ca4b6481e71498712800b20e0c0fcf02843b
	Issue introduced in 6.19 with commit 7bfe3b8ea6e30437e01fcb8e4f56ef6e4d986d0f and fixed in 7.1-rc1 with commit 404cd6bffe17e25e0f94ed2775ffdd6cd10ac3fd

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2026-43348
will be updated if fixes are backported, please check that for the most
up to date information about this issue.


Affected files
==============

The file(s) affected by this issue are:
	drivers/hv/mshv_vtl_main.c
	include/uapi/linux/mshv.h


Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/a142ca4b6481e71498712800b20e0c0fcf02843b
	https://git.kernel.org/stable/c/404cd6bffe17e25e0f94ed2775ffdd6cd10ac3fd