linux-cve-announce - CVE-2025-38506: KVM: Allow CPU to reschedule while setting per-page memory attributes

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Message-ID: <2025081649-CVE-2025-38506-8851@gregkh>
Date: Sat, 16 Aug 2025 12:57:48 +0200
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-38506: KVM: Allow CPU to reschedule while setting per-page memory attributes

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

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

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

KVM: Allow CPU to reschedule while setting per-page memory attributes

When running an SEV-SNP guest with a sufficiently large amount of memory (1TB+),
the host can experience CPU soft lockups when running an operation in
kvm_vm_set_mem_attributes() to set memory attributes on the whole
range of guest memory.

watchdog: BUG: soft lockup - CPU#8 stuck for 26s! [qemu-kvm:6372]
CPU: 8 UID: 0 PID: 6372 Comm: qemu-kvm Kdump: loaded Not tainted 6.15.0-rc7.20250520.el9uek.rc1.x86_64 #1 PREEMPT(voluntary)
Hardware name: Oracle Corporation ORACLE SERVER E4-2c/Asm,MB Tray,2U,E4-2c, BIOS 78016600 11/13/2024
RIP: 0010:xas_create+0x78/0x1f0
Code: 00 00 00 41 80 fc 01 0f 84 82 00 00 00 ba 06 00 00 00 bd 06 00 00 00 49 8b 45 08 4d 8d 65 08 41 39 d6 73 20 83 ed 06 48 85 c0 <74> 67 48 89 c2 83 e2 03 48 83 fa 02 75 0c 48 3d 00 10 00 00 0f 87
RSP: 0018:ffffad890a34b940 EFLAGS: 00000286
RAX: ffff96f30b261daa RBX: ffffad890a34b9c8 RCX: 0000000000000000
RDX: 000000000000001e RSI: 0000000000000000 RDI: 0000000000000000
RBP: 0000000000000018 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffffad890a356868
R13: ffffad890a356860 R14: 0000000000000000 R15: ffffad890a356868
FS:  00007f5578a2a400(0000) GS:ffff97ed317e1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f015c70fb18 CR3: 00000001109fd006 CR4: 0000000000f70ef0
PKRU: 55555554
Call Trace:
 <TASK>
 xas_store+0x58/0x630
 __xa_store+0xa5/0x130
 xa_store+0x2c/0x50
 kvm_vm_set_mem_attributes+0x343/0x710 [kvm]
 kvm_vm_ioctl+0x796/0xab0 [kvm]
 __x64_sys_ioctl+0xa3/0xd0
 do_syscall_64+0x8c/0x7a0
 entry_SYSCALL_64_after_hwframe+0x76/0x7e
RIP: 0033:0x7f5578d031bb
Code: ff ff ff 85 c0 79 9b 49 c7 c4 ff ff ff ff 5b 5d 4c 89 e0 41 5c c3 66 0f 1f 84 00 00 00 00 00 f3 0f 1e fa b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 2d 4c 0f 00 f7 d8 64 89 01 48
RSP: 002b:00007ffe0a742b88 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 000000004020aed2 RCX: 00007f5578d031bb
RDX: 00007ffe0a742c80 RSI: 000000004020aed2 RDI: 000000000000000b
RBP: 0000010000000000 R08: 0000010000000000 R09: 0000017680000000
R10: 0000000000000080 R11: 0000000000000246 R12: 00005575e5f95120
R13: 00007ffe0a742c80 R14: 0000000000000008 R15: 00005575e5f961e0

While looping through the range of memory setting the attributes,
call cond_resched() to give the scheduler a chance to run a higher
priority task on the runqueue if necessary and avoid staying in
kernel mode long enough to trigger the lockup.

The Linux kernel CVE team has assigned CVE-2025-38506 to this issue.


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

	Issue introduced in 6.8 with commit 5a475554db1e476a14216e742ea2bdb77362d5d5 and fixed in 6.12.39 with commit d9bd1163c8d8f716f45e54d034ee28757cc85549
	Issue introduced in 6.8 with commit 5a475554db1e476a14216e742ea2bdb77362d5d5 and fixed in 6.15.7 with commit 1ef45ae7a3938f0844032ba670b4f89180a5bffc
	Issue introduced in 6.8 with commit 5a475554db1e476a14216e742ea2bdb77362d5d5 and fixed in 6.16 with commit 47bb584237cc285e3a860b70c01f7bda9dcfb05b

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-2025-38506
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:
	virt/kvm/kvm_main.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/d9bd1163c8d8f716f45e54d034ee28757cc85549
	https://git.kernel.org/stable/c/1ef45ae7a3938f0844032ba670b4f89180a5bffc
	https://git.kernel.org/stable/c/47bb584237cc285e3a860b70c01f7bda9dcfb05b