CVE-2026-98729 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
x86/mm: Don't apply va_align to hugetlb mappings on AMD F15h
get_align_mask() returns huge_page_mask_align() for hugetlbfs, but get_align_bits() adds va_align.bits regardless, so vm_unmapped_area() returns an address off the huge page boundary and __unmap_hugepage_range() hits BUG_ON(start & ~huge_page_mask(h)) at teardown.
This can be triggered on Carrizo and FX-8370E, both hstates.
Pass the file to get_align_bits() and skip the randomisation for hugetlbfs.
[ bp: Massage commit message. ]
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Analysis
by VulDB Data Team • 10/19/2026
The Linux kernel contains a memory management flaw in the x86 architecture specifically affecting AMD Family 15h processors, such as Carrizo and FX-8370E systems. The vulnerability arises from an incorrect interaction between virtual address alignment logic and huge page mappings within the hugetlbfs subsystem. When allocating or unmapping large pages, the kernel relies on specific alignment masks to ensure that memory addresses adhere to hardware requirements for huge pages. However, a defect in the get_align_bits function causes it to apply va_align bits even when dealing with hugetlbfs mappings where such randomization is inappropriate. While get_align_mask correctly returns the huge_page_mask_align value intended for these large allocations, the subsequent addition of alignment bits by get_align_bits results in calculated virtual addresses that are misaligned relative to the required huge page boundaries.
This technical flaw leads to a critical operational failure during memory teardown operations. Specifically, when the kernel attempts to unmap a range of huge pages using __unmap_hugepage_range, it encounters an address that does not satisfy the alignment constraints enforced by the hardware and kernel checks. This mismatch triggers a BUG_ON assertion within the unmapping routine because the start address fails the check against the huge page mask. Consequently, this results in a kernel panic or system crash on affected AMD processors whenever such memory operations are performed. The issue is reproducible under conditions involving hugetlbfs usage on the specified hardware platforms, effectively causing denial of service through system instability rather than allowing for unauthorized access or data exfiltration.
From a classification perspective, this vulnerability aligns with CWE-682 Incorrect Calculation and CWE-190 Integer Overflow or Wraparound if viewed broadly as a logic error in address arithmetic leading to invalid state assumptions. In the context of attack techniques, it does not represent an exploitable path for privilege escalation but rather represents a stability issue categorized under system availability impacts. The root cause is identified as improper handling of alignment parameters where randomization features are incorrectly applied to memory regions that require strict boundary adherence. This reflects a failure in input validation or parameter filtering within the kernel's virtual memory management subsystem, leading to invalid state transitions during resource deallocation.
Mitigation strategies primarily involve applying the upstream Linux kernel patch that resolves this logic error by modifying get_align_bits to accept file context information and skip randomization for hugetlbfs mappings. System administrators should ensure their kernels are updated with versions containing this fix. For environments where immediate patching is not feasible, limiting the use of hugetlbfs or avoiding workloads on affected AMD Family 15h hardware can reduce exposure to the crash condition. Monitoring system logs for kernel panics related to memory management and huge page unmaps may assist in identifying instances where this vulnerability has been triggered. Continuous integration of security updates remains the most effective defense against such low-level kernel defects that compromise system stability.