CVE-2026-89827 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
drm/amdgpu: avoid force-completing uninitialized UVD rings
uvd_v7_0_sw_init() does not initialize the UVD decode ring for an SR-IOV VF. However, amdgpu_uvd_resume() unconditionally force-completes the decode ring when restoring its fence sequence.
Skip fence completion when the fence driver is not initialized.
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Analysis
by VulDB Data Team • 09/16/2026
The vulnerability identified in the Linux kernel's AMDGPU DRM subsystem involves a critical initialization flaw within the UVD (Unified Video Decoder) hardware management code, specifically affecting SR-IOV virtual function environments. The core issue stems from an inconsistency in how the UVD decode ring is handled during driver startup and resume operations. In single-root I/O virtualization configurations, the software initialization routine uvd_v7_0_sw_init fails to properly initialize the UVD decode ring for the virtualized instance. This leaves the internal state of the fence driver associated with that ring in an undefined or uninitialized condition, effectively creating a gap between the expected operational state and the actual memory layout.
The severity of this flaw is realized during system resume operations when the function amdgpu_uvd_resume is invoked to restore hardware states from sleep modes. This routine unconditionally attempts to force-complete the decode ring by updating its fence sequence number without first verifying whether the underlying fence driver has been correctly initialized. Because the initialization step was skipped for SR-IOV virtual functions, this unconditional operation targets uninitialized memory structures or invalid pointers. Such an action constitutes a use-of-uninitialized-resource error, which can lead to unpredictable kernel behavior including potential crashes, data corruption within GPU command buffers, or security-relevant information leaks if sensitive kernel memory is inadvertently read during the faulty completion process.
From a vulnerability classification perspective, this defect aligns with CWE-908, Use of Uninitialized Resource, as it involves accessing hardware resources that have not been properly set up by the driver framework. Furthermore, in the context of attack techniques, this flaw could potentially be leveraged for denial-of-service attacks against virtualized environments if an attacker can trigger resume cycles repeatedly to cause kernel panics or instability within the guest operating system. It also touches upon CWE-672, Use of Outside-Controlled Memory, as the driver relies on internal state that may not reflect the actual hardware readiness due to the SR-IOV abstraction layer's specific initialization requirements being overlooked.
The operational impact is primarily centered around stability and reliability in virtualized desktop or server environments utilizing AMD GPUs with UVD capabilities. Users running multiple virtual machines under an SR-IOV hypervisor configuration are at risk of experiencing system hangs or kernel oops messages when the host machine resumes from a suspended state. While direct remote code execution is unlikely due to the nature of the fault being internal driver logic, the instability can disrupt critical workloads and compromise the isolation guarantees provided by virtualization technologies if memory corruption occurs adjacent to other sensitive structures in kernel space.
To mitigate this vulnerability, the recommended approach involves ensuring that all hardware resources are explicitly initialized before any resume or force-completion operations are attempted. The fix implemented addresses this by adding a conditional check within amdgpu_uvd_resume to verify whether the fence driver for the decode ring is properly initialized. If the initialization has not occurred, particularly in SR-IOV virtual function contexts, the routine now skips the forced completion step rather than executing it blindly. This defensive programming practice ensures that operations are only performed on valid, ready-to-use resources. System administrators should apply kernel updates containing this patch to restore stability and security integrity for AMDGPU-based systems operating in virtualized environments.