From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: linux-cve-announce@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@kernel.org>
Subject: CVE-2026-43315: KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding
Date: Fri, 8 May 2026 15:12:20 +0200 [thread overview]
Message-ID: <2026050801-CVE-2026-43315-3359@gregkh> (raw)
From: Greg Kroah-Hartman <gregkh@kernel.org>
Description
===========
In the Linux kernel, the following vulnerability has been resolved:
KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding
Drop the WARN in svm_set_nested_state() on nested_svm_load_cr3() failing
as it is trivially easy to trigger from userspace by modifying CPUID after
loading CR3. E.g. modifying the state restoration selftest like so:
--- tools/testing/selftests/kvm/x86/state_test.c
+++ tools/testing/selftests/kvm/x86/state_test.c
@@ -280,7 +280,16 @@ int main(int argc, char *argv[])
/* Restore state in a new VM. */
vcpu = vm_recreate_with_one_vcpu(vm);
- vcpu_load_state(vcpu, state);
+
+ if (stage == 4) {
+ state->sregs.cr3 = BIT(44);
+ vcpu_load_state(vcpu, state);
+
+ vcpu_set_cpuid_property(vcpu, X86_PROPERTY_MAX_PHY_ADDR, 36);
+ __vcpu_nested_state_set(vcpu, &state->nested);
+ } else {
+ vcpu_load_state(vcpu, state);
+ }
/*
* Restore XSAVE state in a dummy vCPU, first without doing
generates:
WARNING: CPU: 30 PID: 938 at arch/x86/kvm/svm/nested.c:1877 svm_set_nested_state+0x34a/0x360 [kvm_amd]
Modules linked in: kvm_amd kvm irqbypass [last unloaded: kvm]
CPU: 30 UID: 1000 PID: 938 Comm: state_test Tainted: G W 6.18.0-rc7-58e10b63777d-next-vm
Tainted: [W]=WARN
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
RIP: 0010:svm_set_nested_state+0x34a/0x360 [kvm_amd]
Call Trace:
<TASK>
kvm_arch_vcpu_ioctl+0xf33/0x1700 [kvm]
kvm_vcpu_ioctl+0x4e6/0x8f0 [kvm]
__x64_sys_ioctl+0x8f/0xd0
do_syscall_64+0x61/0xad0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
Simply delete the WARN instead of trying to prevent userspace from shoving
"illegal" state into CR3. For better or worse, KVM's ABI allows userspace
to set CPUID after SREGS, and vice versa, and KVM is very permissive when
it comes to guest CPUID. I.e. attempting to enforce the virtual CPU model
when setting CPUID could break userspace. Given that the WARN doesn't
provide any meaningful protection for KVM or benefit for userspace, simply
drop it even though the odds of breaking userspace are minuscule.
Opportunistically delete a spurious newline.
The Linux kernel CVE team has assigned CVE-2026-43315 to this issue.
Affected and fixed versions
===========================
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 5.15.202 with commit 155ec243ef726f4bc49536fa0bfb565dc011ab17
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 6.1.165 with commit 580ea57840864d40e019bc13fd26afdc8d510a2f
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 6.6.128 with commit deb8f6dfd31d94b18dbeeaa8c01fbec5fc70fd2b
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 6.12.75 with commit ce904c8a5bbe697eae0f7e34b07095bd7a6dee19
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 6.18.16 with commit 969e5e13ff5c18603f21d1f9f64ec9194e141ac0
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 6.19.6 with commit ebb2ab4f1c87d6b52776292cf7dc16aea48e95f8
Issue introduced in 5.14 with commit b222b0b88162bdef4eceb12a79d5edbbdb23dbfd and fixed in 7.0 with commit fc3ba56385d03501eb582e4b86691ba378e556f9
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-2026-43315
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/svm/nested.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/155ec243ef726f4bc49536fa0bfb565dc011ab17
https://git.kernel.org/stable/c/580ea57840864d40e019bc13fd26afdc8d510a2f
https://git.kernel.org/stable/c/deb8f6dfd31d94b18dbeeaa8c01fbec5fc70fd2b
https://git.kernel.org/stable/c/ce904c8a5bbe697eae0f7e34b07095bd7a6dee19
https://git.kernel.org/stable/c/969e5e13ff5c18603f21d1f9f64ec9194e141ac0
https://git.kernel.org/stable/c/ebb2ab4f1c87d6b52776292cf7dc16aea48e95f8
https://git.kernel.org/stable/c/fc3ba56385d03501eb582e4b86691ba378e556f9
reply other threads:[~2026-05-08 13:15 UTC|newest]
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