CVE-2026-74524: riscv: mm: Fix out-of-bounds page-table walk during memory hot-remove

From: Greg Kroah-Hartman <[email protected]>

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

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

riscv: mm: Fix out-of-bounds page-table walk during memory hot-remove

remove_pud_mapping() and remove_p4d_mapping() obtain a child table base
with pud_offset(p4dp, 0) and p4d_offset(pgd, 0), then add the index for
addr.

RISC-V folds page-table levels at runtime. When a level is folded, its
offset helper returns the parent entry itself, but the index can still be
nonzero. Adding it walks past the parent table. Sv48 folds P4D, while Sv39
folds both P4D and PUD, so memory hot-remove can descend into unrelated
memory and pass an invalid page to __free_pages(). This can trigger:

  kernel BUG at include/linux/mm.h:1810!
  VM_BUG_ON_PAGE(page_ref_count(page) == 0)
  arch_remove_memory+0x1e/0x5c
  try_remove_memory+0x15e/0x200
  remove_memory+0x24/0x3c

Only add the index when the corresponding page-table level is enabled,
matching p4d_offset() and pud_offset().

The Linux kernel CVE team has assigned CVE-2026-74524 to this issue.


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

	Issue introduced in 6.11 with commit c75a74f4ba19c904c0ae1e011ae2568449409ae4 and fixed in 6.12.103 with commit 1da6d832eda02d908df11a30ba6a856b98a3dd76
	Issue introduced in 6.11 with commit c75a74f4ba19c904c0ae1e011ae2568449409ae4 and fixed in 6.18.44 with commit 54e07a158f7aea2754849d3a5a4cba1ac338ae7e
	Issue introduced in 6.11 with commit c75a74f4ba19c904c0ae1e011ae2568449409ae4 and fixed in 7.1.8 with commit 1bb0ef8069ef158d245bac91ac178bb4f1a7ccd2
	Issue introduced in 6.11 with commit c75a74f4ba19c904c0ae1e011ae2568449409ae4 and fixed in 7.2-rc6 with commit a0188cc133696627857d16054e43f9ebc7efc821

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-2026-74524
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:
	arch/riscv/mm/init.c


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/1da6d832eda02d908df11a30ba6a856b98a3dd76
	https://git.kernel.org/stable/c/54e07a158f7aea2754849d3a5a4cba1ac338ae7e
	https://git.kernel.org/stable/c/1bb0ef8069ef158d245bac91ac178bb4f1a7ccd2
	https://git.kernel.org/stable/c/a0188cc133696627857d16054e43f9ebc7efc821