CVE-2026-80867 in Linux
Summary
by MITRE • 09/04/2026
In the Linux kernel, the following vulnerability has been resolved:
alpha/PCI: Add security_locked_down() check to pci_mmap_resource()
Currently, Alpha's pci_mmap_resource() does not check security_locked_down(LOCKDOWN_PCI_ACCESS) before allowing userspace to mmap PCI BARs.
The generic version has had this check since commit eb627e17727e ("PCI: Lock down BAR access when the kernel is locked down") to prevent DMA attacks when the kernel is locked down.
Add the same check to Alpha's pci_mmap_resource().
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Analysis
by VulDB Data Team • 09/04/2026
The Linux kernel implements a security lockdown mechanism designed to restrict certain operations that could be exploited by an attacker who has gained user-level access but does not possess full root privileges or physical control over the hardware. This feature is particularly critical in environments where system integrity must be maintained even if the initial attack surface, such as a web server or container runtime, is compromised. The lockdown mechanism includes various levels of restriction, one of which targets direct memory access through PCI bus resources. Specifically, the LOCKDOWN_PCI_ACCESS flag prevents unprivileged users from mapping Physical Address Range (BAR) regions into user space via mmap operations. This restriction exists to mitigate Direct Memory Access attacks, where malicious software could potentially read or write to kernel memory or other devices by exploiting DMA capabilities inherent in PCI hardware.
In the Alpha architecture implementation of the Linux kernel, a specific inconsistency was identified within the pci_mmap_resource function. While the generic x86 and ARM implementations correctly enforced this security check prior to allowing userspace mapping of PCI BARs, the Alpha-specific code path lacked this validation. This omission meant that on systems running the Alpha port of the Linux kernel, an attacker could bypass the lockdown policy by directly requesting memory mappings for PCI device resources. By exploiting this gap, a compromised user-space process could potentially access sensitive kernel data structures or interact with hardware devices in ways intended to be prohibited when the system is locked down. This represents a significant deviation from the security posture established across other architectures and undermines the effectiveness of the lockdown feature on Alpha-based systems.
The operational impact of this vulnerability allows for potential DMA attacks that were previously mitigated by the generic PCI subsystem code. An attacker leveraging this flaw could read confidential information stored in kernel memory or modify hardware state, leading to privilege escalation or data exfiltration. This is particularly dangerous because it bypasses standard access controls enforced when the kernel security lockdown is active, such as during secure boot processes or when running with strict integrity policies enabled via sysctl parameters like kernel.lockdown. The absence of this check creates a consistent attack vector across Alpha systems that does not exist on other supported architectures, creating an uneven security landscape within the Linux ecosystem.
To address this issue, developers integrated the security_locked_down(LOCKDOWN_PCI_ACCESS) check into the alpha/PCI pci_mmap_resource function. This change aligns the Alpha architecture implementation with the generic PCI subsystem behavior established in commit eb627e17727e. By enforcing this check, the kernel now correctly denies userspace mmap requests for PCI BARs when the lockdown mode is active and restricts access to DMA-capable resources that could be used for malicious memory manipulation. This fix ensures parity with other architectures and restores the intended security boundary defined by the Linux kernel lockdown mechanism.
From a classification perspective, this vulnerability falls under CWE-284 Improper Access Control, as it involves an insufficient check of user permissions before granting access to protected system resources. It also relates to CWE-732 Incorrect Permission Assignment for Critical Resource, specifically regarding the assignment of memory mapping privileges without verifying the security context. In terms of adversary tactics, this flaw facilitates techniques associated with MITRE ATT&CK ID T1055, which covers Process Memory Manipulation via DMA attacks. The vulnerability allows an attacker to bypass standard process isolation mechanisms by directly accessing physical memory through PCI devices. Mitigation requires applying the kernel patch that introduces the security_locked_down check for Alpha architectures. System administrators should ensure their kernels are updated to include this fix and verify that lockdown modes are appropriately configured based on threat models, as enabling LOCKDOWN_PCI_ACCESS is essential for preventing these specific DMA-based exploitation paths when running in a locked-down state.