CVE-2026-98003 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
iommu/amd: Do not reallocate GA log buffers on resume
Commit c5e1a1eb9279 ("iommu/amd: Simplify and Consolidate Virtual APIC (AVIC) Enablement") moved the GA log allocation from iommu_init_pci() to enable_iommus_vapic(), which is called on every resume.
iommu_init_ga_log() assigns iommu->ga_log and iommu->ga_log_tail unconditionally. Each resume therefore replaces the boot-time pointers and leaks both old allocations. The function also uses GFP_KERNEL from a syscore resume callback, where interrupts are disabled and the non-boot CPUs are offline.
Return early if both buffers are already allocated. Clear the pointers in free_ga_log() so a partial allocation failure cannot leave ga_log dangling.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified within the Linux kernel's AMD IOMMU subsystem stems from an improper memory management strategy during system resume operations, specifically related to Guest Address (GA) log buffers used for Virtual APIC functionality. The root cause was introduced by a prior refactoring commit that relocated the allocation of these GA log buffers from the initial PCI initialization phase into the enable_iommus_vapic function. This relocation inadvertently caused the allocation routine to execute during every system resume cycle rather than only once at boot time. Consequently, each resumption event triggers an unconditional assignment of new memory pointers for iommu->ga_log and iommu->ga_log_tail without first checking if valid buffers already exist from a previous initialization or prior resume state.
This logic flaw results in two distinct technical issues that compromise system stability and security posture. First, the failure to check existing allocations leads to a classic resource leak where previously allocated memory is not freed before being overwritten by new pointers. Over repeated suspend-resume cycles, this accumulates into significant kernel memory exhaustion, potentially leading to out-of-memory conditions or general instability within the operating environment. Second, and more critically from an operational safety perspective, the allocation routine utilizes GFP_KERNEL flags while executing inside a syscore resume callback context. In this specific execution phase, hardware interrupts are disabled and non-boot CPUs are offline, creating an unsafe environment for memory allocations that might sleep or require scheduling capabilities typically unavailable in such atomic contexts. This mismatch between allocation requirements and runtime constraints can trigger kernel panics or undefined behavior if the allocator attempts to perform operations incompatible with the current interrupt state.
The operational impact of this vulnerability extends beyond simple resource leakage. The potential for a partial allocation failure leaving dangling pointers introduces a risk of use-after-free scenarios or null pointer dereferences in subsequent IOMMU operations that rely on these log buffers. If free_ga_log does not properly clear references after deallocation, stale pointers may persist and be accessed by other subsystems expecting valid memory regions. This creates an attack surface where local attackers could potentially exploit the instability to cause denial of service against critical system functions or attempt to manipulate kernel state through corrupted pointer values. The issue is classified under CWE-401 for missing release of memory after effective allocation, which directly contributes to resource exhaustion and potential code execution vulnerabilities if the dangling pointers are leveraged in specific exploitation chains.
To mitigate this vulnerability, the remediation strategy involves modifying the enable_iommus_vapic logic to include a guard clause that checks whether both GA log buffers have already been allocated before attempting new allocations. This ensures idempotency during resume events and prevents redundant memory consumption. Additionally, the free_ga_log function must be updated to explicitly nullify or clear the ga_log pointers upon deallocation. This practice eliminates dangling references and ensures that any subsequent checks for allocation status accurately reflect the current state of memory resources. These changes align with ATT&CK technique T1496 regarding Resource Hijacking through resource exhaustion, as they address the underlying mechanism allowing attackers to degrade system availability via uncontrolled resource consumption during routine power management transitions.