CVE-2022-39188 Overview
CVE-2022-39188 is a race condition vulnerability discovered in the Linux kernel's TLB (Translation Lookaside Buffer) handling code located in include/asm-generic/tlb.h. The vulnerability exists in Linux kernel versions prior to 5.19 and arises from a race condition between unmap_mapping_range and munmap operations. This flaw allows a device driver to potentially free a page while stale TLB entries still reference it, which only occurs in specific situations involving VM_PFNMAP VMAs (Virtual Memory Areas with Physical Frame Number mapping).
Critical Impact
A local attacker with low privileges could exploit this race condition to cause a denial of service condition by triggering use of freed memory pages through stale TLB entries, potentially leading to system instability or crashes.
Affected Products
- Linux Kernel (versions prior to 5.19)
- Debian Linux 10.0
- Debian Linux 11.0
Discovery Timeline
- 2022-09-02 - CVE-2022-39188 published to NVD
- 2024-11-21 - Last updated in NVD database
Technical Details for CVE-2022-39188
Vulnerability Analysis
This vulnerability is classified as CWE-362 (Race Condition). The issue manifests in the kernel's memory management subsystem, specifically within the TLB flush mechanisms for VM_PFNMAP virtual memory areas.
The race condition occurs when two concurrent operations—unmap_mapping_range and munmap—interact in an unsafe manner. VM_PFNMAP VMAs are special memory mappings that directly map physical frame numbers rather than using standard page table entries. Device drivers commonly use these mappings to provide user-space access to hardware resources or memory-mapped I/O regions.
When the race condition triggers, a device driver may free a physical page while the CPU's TLB still contains cached translations pointing to that page. Subsequent memory accesses using these stale TLB entries can result in use-after-free conditions at the memory management level, leading to potential system instability, kernel panics, or denial of service.
Root Cause
The root cause lies in insufficient synchronization between TLB invalidation operations and page deallocation for VM_PFNMAP VMAs. The kernel's mmu_gather structure, which batches TLB flush operations for performance, did not properly account for the special handling requirements of VM_PFNMAP mappings. This oversight allowed a timing window where page frames could be freed before all CPUs had flushed their cached TLB entries for those pages.
Attack Vector
The attack vector is local, requiring an attacker to have low-privilege access to the target system. Exploitation requires the ability to trigger specific memory mapping operations that utilize VM_PFNMAP VMAs, typically through interaction with device drivers that expose such mappings to user space. The attack complexity is considered high due to the precise timing required to exploit the race condition window.
The vulnerability was documented in Project Zero Issue #2329, which provides detailed technical analysis of the race condition mechanics.
// Security patch from include/asm-generic/tlb.h
// Source: https://github.com/torvalds/linux/commit/b67fbebd4cf980aecbcc750e1462128bffe8ae15
*/
unsigned int vma_exec : 1;
unsigned int vma_huge : 1;
+ unsigned int vma_pfn : 1;
unsigned int batch_count;
The patch adds a new vma_pfn flag to the mmu_gather structure, enabling the kernel to track VM_PFNMAP VMAs and force TLB flushes appropriately before page deallocation.
Detection Methods for CVE-2022-39188
Indicators of Compromise
- Unexpected kernel panics or system crashes related to memory management operations
- Kernel log messages indicating use-after-free conditions or invalid page table entries
- System instability when interacting with device drivers that use VM_PFNMAP mappings
- Memory corruption symptoms in applications utilizing memory-mapped device regions
Detection Strategies
- Monitor kernel version to identify systems running Linux kernel versions prior to 5.19
- Implement kernel log monitoring for TLB-related errors or memory management warnings
- Deploy endpoint detection tools capable of identifying kernel-level race condition exploitation attempts
- Audit systems for device drivers that utilize VM_PFNMAP mappings and assess exposure
Monitoring Recommendations
- Configure centralized logging to capture kernel messages related to memory management subsystem errors
- Establish baseline kernel behavior and alert on anomalous TLB flush patterns or memory deallocation sequences
- Monitor system stability metrics and investigate unexpected reboots or kernel panics
How to Mitigate CVE-2022-39188
Immediate Actions Required
- Update Linux kernel to version 5.19 or later which contains the security fix
- Apply distribution-specific security patches from Debian or other vendors
- Prioritize patching on systems with device drivers that expose VM_PFNMAP mappings to user space
- Consider restricting access to affected device drivers until patches can be applied
Patch Information
The vulnerability has been addressed in Linux kernel version 5.19 through commit b67fbebd4cf980aecbcc750e1462128bffe8ae15. The fix introduces proper tracking of VM_PFNMAP VMAs in the TLB management code to ensure forced TLB flushes before page deallocation.
Key resources for patching:
Workarounds
- Limit user access to device drivers that utilize VM_PFNMAP VMAs where possible
- Implement access controls to restrict which users can interact with memory-mapped device regions
- Consider disabling or unloading non-essential device drivers that expose VM_PFNMAP mappings until patching is complete
# Check current kernel version
uname -r
# For Debian-based systems, update to patched kernel
sudo apt update
sudo apt upgrade linux-image-$(uname -r)
# Reboot to apply kernel update
sudo reboot
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
