Linux Kernel up to 6.12.53/6.17.3 kvm ioremap_cache initialization

Summaryinfo

A vulnerability was found in Linux Kernel up to 6.12.53/6.17.3. It has been rated as critical. This affects the function ioremap_cache of the component kvm. Performing a manipulation results in initialization. This vulnerability is identified as CVE-2025-40181. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in Linux Kernel up to 6.12.53/6.17.3. It has been classified as critical. This affects the function ioremap_cache of the component kvm. The manipulation with an unknown input leads to a initialization vulnerability. CWE is classifying the issue as CWE-665. The product does not initialize or incorrectly initializes a resource, which might leave the resource in an unexpected state when it is accessed or used. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

In the Linux kernel, the following vulnerability has been resolved: x86/kvm: Force legacy PCI hole to UC when overriding MTRRs for TDX/SNP When running as an SNP or TDX guest under KVM, force the legacy PCI hole, i.e. memory between Top of Lower Usable DRAM and 4GiB, to be mapped as UC via a forced variable MTRR range. In most KVM-based setups, legacy devices such as the HPET and TPM are enumerated via ACPI. ACPI enumeration includes a Memory32Fixed entry, and optionally a SystemMemory descriptor for an OperationRegion, e.g. if the device needs to be accessed via a Control Method. If a SystemMemory entry is present, then the kernel's ACPI driver will auto-ioremap the region so that it can be accessed at will. However, the ACPI spec doesn't provide a way to enumerate the memory type of SystemMemory regions, i.e. there's no way to tell software that a region must be mapped as UC vs. WB, etc. As a result, Linux's ACPI driver always maps SystemMemory regions using ioremap_cache(), i.e. as WB on x86. The dedicated device drivers however, e.g. the HPET driver and TPM driver, want to map their associated memory as UC or WC, as accessing PCI devices using WB is unsupported. On bare metal and non-CoCO, the conflicting requirements "work" as firmware configures the PCI hole (and other device memory) to be UC in the MTRRs. So even though the ACPI mappings request WB, they are forced to UC- in the kernel's tracking due to the kernel properly handling the MTRR overrides, and thus are compatible with the drivers' requested WC/UC-. With force WB MTRRs on SNP and TDX guests, the ACPI mappings get their requested WB if the ACPI mappings are established before the dedicated driver code attempts to initialize the device. E.g. if acpi_init() runs before the corresponding device driver is probed, ACPI's WB mapping will "win", and result in the driver's ioremap() failing because the existing WB mapping isn't compatible with the requested WC/UC-. E.g. when a TPM is emulated by the hypervisor (ignoring the security implications of relying on what is allegedly an untrusted entity to store measurements), the TPM driver will request UC and fail: [ 1.730459] ioremap error for 0xfed40000-0xfed45000, requested 0x2, got 0x0 [ 1.732780] tpm_tis MSFT0101:00: probe with driver tpm_tis failed with error -12 Note, the '0x2' and '0x0' values refer to "enum page_cache_mode", not x86's memtypes (which frustratingly are an almost pure inversion; 2 == WB, 0 == UC). E.g. tracing mapping requests for TPM TIS yields: Mapping TPM TIS with req_type = 0 WARNING: CPU: 22 PID: 1 at arch/x86/mm/pat/memtype.c:530 memtype_reserve+0x2ab/0x460 Modules linked in: CPU: 22 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.16.0-rc7+ #2 VOLUNTARY Tainted: [W]=WARN Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/29/2025 RIP: 0010:memtype_reserve+0x2ab/0x460 __ioremap_caller+0x16d/0x3d0 ioremap_cache+0x17/0x30 x86_acpi_os_ioremap+0xe/0x20 acpi_os_map_iomem+0x1f3/0x240 acpi_os_map_memory+0xe/0x20 acpi_ex_system_memory_space_handler+0x273/0x440 acpi_ev_address_space_dispatch+0x176/0x4c0 acpi_ex_access_region+0x2ad/0x530 acpi_ex_field_datum_io+0xa2/0x4f0 acpi_ex_extract_from_field+0x296/0x3e0 acpi_ex_read_data_from_field+0xd1/0x460 acpi_ex_resolve_node_to_value+0x2ee/0x530 acpi_ex_resolve_to_value+0x1f2/0x540 acpi_ds_evaluate_name_path+0x11b/0x190 acpi_ds_exec_end_op+0x456/0x960 acpi_ps_parse_loop+0x27a/0xa50 acpi_ps_parse_aml+0x226/0x600 acpi_ps_execute_method+0x172/0x3e0 acpi_ns_evaluate+0x175/0x5f0 acpi_evaluate_object+0x213/0x490 acpi_evaluate_integer+0x6d/0x140 acpi_bus_get_status+0x93/0x150 acpi_add_single_object+0x43a/0x7c0 acpi_bus_check_add+0x149/0x3a0 acpi_bus_check_add_1+0x16/0x30 acpi_ns_walk_namespace+0x22c/0x360 acpi_walk_namespace+0x15c/0x170 acpi_bus_scan+0x1dd/0x200 acpi_scan_init+0xe5/0x2b0 acpi_init+0x264/0x5b0 do_one_i ---truncated---

The advisory is shared at git.kernel.org. This vulnerability is uniquely identified as CVE-2025-40181 since 04/16/2025. The exploitability is told to be difficult. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 02/05/2026).

The vulnerability scanner Nessus provides a plugin with the ID 275354 (Linux Distros Unpatched Vulnerability : CVE-2025-40181), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.12.54, 6.17.4 or 6.18-rc1 eliminates this vulnerability. Applying the patch 34ff466f74d0fe1db8956f9c245e2bb2c67f67bf/91ab8a21bda2d2d2842b6159ac060d9100433a3c/0dccbc75e18df85399a71933d60b97494110f559 is able to eliminate this problem. The bugfix is ready for download at git.kernel.org. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (275354) and CERT Bund (WID-SEC-2025-2595). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• Google Container-Optimized OS
• Debian Linux
• Amazon Linux 2
• Red Hat Enterprise Linux
• SUSE Linux
• Oracle Linux
• SUSE openSUSE
• Open Source Linux Kernel
• RESF Rocky Linux

Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 6.12.0
• 6.12.1
• 6.12.2
• 6.12.3
• 6.12.4
• 6.12.5
• 6.12.6
• 6.12.7
• 6.12.8
• 6.12.9
• 6.12.10
• 6.12.11
• 6.12.12
• 6.12.13
• 6.12.14
• 6.12.15
• 6.12.16
• 6.12.17
• 6.12.18
• 6.12.19
• 6.12.20
• 6.12.21
• 6.12.22
• 6.12.23
• 6.12.24
• 6.12.25
• 6.12.26
• 6.12.27
• 6.12.28
• 6.12.29
• 6.12.30
• 6.12.31
• 6.12.32
• 6.12.33
• 6.12.34
• 6.12.35
• 6.12.36
• 6.12.37
• 6.12.38
• 6.12.39
• 6.12.40
• 6.12.41
• 6.12.42
• 6.12.43
• 6.12.44
• 6.12.45
• 6.12.46
• 6.12.47
• 6.12.48
• 6.12.49
• 6.12.50
• 6.12.51
• 6.12.52
• 6.12.53
• 6.17.0
• 6.17.1
• 6.17.2
• 6.17.3

License

• open-source

Website

• Vendor: https://www.kernel.org/

CPE 2.3info

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CPE 2.2info

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Exploitinginfo

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Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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