linux-cve-announce - CVE-2025-21740: KVM: x86/mmu: Ensure NX huge page recovery thread is alive before waking

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Message-ID: <2025022659-CVE-2025-21740-083e@gregkh>
Date: Wed, 26 Feb 2025 18:11:22 -0800
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: CVE-2025-21740: KVM: x86/mmu: Ensure NX huge page recovery thread is alive before waking

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

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

KVM: x86/mmu: Ensure NX huge page recovery thread is alive before waking

When waking a VM's NX huge page recovery thread, ensure the thread is
actually alive before trying to wake it.  Now that the thread is spawned
on-demand during KVM_RUN, a VM without a recovery thread is reachable via
the related module params.

  BUG: kernel NULL pointer dereference, address: 0000000000000040
  #PF: supervisor read access in kernel mode
  #PF: error_code(0x0000) - not-present page
  Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
  RIP: 0010:vhost_task_wake+0x5/0x10
  Call Trace:
   <TASK>
   set_nx_huge_pages+0xcc/0x1e0 [kvm]
   param_attr_store+0x8a/0xd0
   module_attr_store+0x1a/0x30
   kernfs_fop_write_iter+0x12f/0x1e0
   vfs_write+0x233/0x3e0
   ksys_write+0x60/0xd0
   do_syscall_64+0x5b/0x160
   entry_SYSCALL_64_after_hwframe+0x4b/0x53
  RIP: 0033:0x7f3b52710104
   </TASK>
  Modules linked in: kvm_intel kvm
  CR2: 0000000000000040

The Linux kernel CVE team has assigned CVE-2025-21740 to this issue.


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

	Issue introduced in 6.14-rc1 with commit 931656b9e2ff7029aee0b36e17780621948a6ac1 and fixed in 6.14-rc2 with commit 43fb96ae78551d7bfa4ecca956b258f085d67c40

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-2025-21740
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/x86/kvm/mmu/mmu.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/2b3928b7c896e5a9fb6b1373924adafe8e01a0c6
	https://git.kernel.org/stable/c/974f85f1f7eb7dc7fce0988046e06eeccab576a7
	https://git.kernel.org/stable/c/43fb96ae78551d7bfa4ecca956b258f085d67c40