The Linux kernel vulnerability tracked as CVE‑2024‑50177 stems from a benign‑looking arithmetic edge case in the AMD display math library (DML2.1) that triggers a UBSan (Undefined Behavior Sanitizer) shift‑out‑of‑bounds warning and can cause driver instability; vendors have issued patches and distribution security advisories class this as a medium‑severity, availability‑focused flaw with a CVSS v3 base score of 5.5.
The affected code lives inside the AMD display stack used by the amdgpu DRM driver. DML (Display Math Library) is a small, heavily optimized calculation engine used by AMD’s driver to compute timing, plane placement, cursor and stream attributes for Display Core Next (DCN) hardware. In DML2.1 a corner case can arise when the driver programs a so‑called phantom pipe (a non‑visible/placeholder pipeline) where the cursor width is explicitly set to zero; a downstream calculation then constructs a shift operation whose exponent underflows or becomes excessively large for the 32‑bit unsigned type used, triggering UBSAN’s shift‑out‑of‑bounds check at runtime. This is a correctness/hardening issue rather than a classic memory corruption that immediately enables code execution. The practical impact is an availability problem — noisy kernel logs, potential driver warnings, or deterministic failures on systems exercising the affected path — and therefore the remediation approach focused on a small defensive code fix in the amdgpu/DML codepath and distribution kernel updates. Multiple vendor trackers and distributions (Ubuntu, SUSE, Debian, openSUSE, Amazon Linux advisories) recorded the CVE and provided fixed package mappings.
Source: MSRC Security Update Guide - Microsoft Security Response Center
Background / Overview
The affected code lives inside the AMD display stack used by the amdgpu DRM driver. DML (Display Math Library) is a small, heavily optimized calculation engine used by AMD’s driver to compute timing, plane placement, cursor and stream attributes for Display Core Next (DCN) hardware. In DML2.1 a corner case can arise when the driver programs a so‑called phantom pipe (a non‑visible/placeholder pipeline) where the cursor width is explicitly set to zero; a downstream calculation then constructs a shift operation whose exponent underflows or becomes excessively large for the 32‑bit unsigned type used, triggering UBSAN’s shift‑out‑of‑bounds check at runtime. This is a correctness/hardening issue rather than a classic memory corruption that immediately enables code execution. The practical impact is an availability problem — noisy kernel logs, potential driver warnings, or deterministic failures on systems exercising the affected path — and therefore the remediation approach focused on a small defensive code fix in the amdgpu/DML codepath and distribution kernel updates. Multiple vendor trackers and distributions (Ubuntu, SUSE, Debian, openSUSE, Amazon Linux advisories) recorded the CVE and provided fixed package mappings. What happened technically
The root cause in plain terms
- When the driver sets up a phantom pipe, it sets cursor_width to 0 to indicate there is no hardware cursor for that pipe.
- Later, a DML calculation computes an exponent or shift amount that involves expressions like (some_value - cursor_width) or related derived values.
- Because cursor_width is zero and types are unsigned 32‑bit integers, the calculation produces an unexpectedly large unsigned exponent (effectively underflowing when interpreted as a signed adjustment), which is invalid for a left‑shift operation and triggers UBSAN’s shift‑out‑of‑bounds runtime trap.
- UBSAN reports a message similar to: "shift exponent 4294967170 is too large for 32‑bit type 'unsigned int'". The kernel’s UBSAN handler then prints a stack trace pointing to calculate_cursor_req_attributes and the DML core mode support routines.
Why UBSAN caught it (and why that’s good)
UBSan is a runtime sanitizer that catches undefined behavior (including invalid shift operations) that could otherwise produce platform‑dependent or silent corruptions. Because this problem surfaced under UBSAN (or when running kernels compiled with UBSAN instrumentation) it allowed maintainers and testers to detect the exact arithmetic mismatch early and implement a defensive fix rather than waiting for a field crash that might be noisier or harder to reproduce. The advisories show the stack trace and the exact DML source file line implicated, making the fix surgical and straightforward to verify.Affected components and exposure
Components
- Vulnerable module: Linux kernel DRM — drm/amd/display (amdgpu + DML2.1 math routines).
- Faulty code region: DML2.1 source (for example dml2_core_dcn4_calcs.c in DML2.1), specific function calculate_cursor_req_attributes and related mode‑support code paths. The failure trace in vendor advisories pinpoints the file and the approximate line number reported by UBSAN.
Platforms and realistic exposure model
- Systems that run kernels compiled with the amdgpu display stack and that can reach the DML2.1 code paths are potentially affected. In practice that includes many desktop/workstation Linux distributions using AMD GPUs with DCN hardware where the driver uses DML2.1.
- The attack vector is local and low complexity: an unprivileged process or compositor that triggers certain modesetting or pipe programming flows (hot‑plug, MST, phantom pipe setup, or specialized test/harness paths) can exercise the condition.
- For mainstream single‑user desktops with modern compositors and standard hardware, the chance of hitting the phantom pipe + cursor_width==0 arithmetic corner is relatively low, but the long tail (embedded boards, OEM kernels, developer/test harnesses) increases exposure. Distributions classified this CVE as medium because of the availability impact and local attack vector.
The fix and verification
What maintainers changed
- The upstream kernel change is small and defensive: make the DML arithmetic robust to zero cursor_width (either by ensuring proper signed/unsigned handling, bounding the exponent, or short‑circuiting the calculation when cursor width is zero) so the shift operation is never invoked with an out‑of‑range exponent.
- The patch is intentionally surgical — avoid large refactors in the timing code and instead guard the arithmetic expression or change type/overflow checks so UBSAN’s check is satisfied and runtime behavior is defined.
How distributions and vendors applied it
- The upstream commits were cherry‑picked into stable kernel branches and backported into distribution kernels. Multiple vendors (Ubuntu, SUSE, Debian, openSUSE and others) published advisories and mapped fixed package versions; those entries list the CVE and the fix description so administrators can confirm whether their kernel package contains the change.
- Microsoft’s security update guide cataloged the CVE and the Microsoft artifact mapping for Azure/Linux images, and advised operators to consult vendor changelogs for remediation status in their images. For broader operational guidance on AMD DRM driver fixes and kernel updates, refer to vendor advisories and distribution trackers.
How to verify the fix on your systems
- Check the running kernel: uname -r.
- Inspect package changelogs or your distribution’s security tracker for CVE‑2024‑50177 or the upstream stable commit ID that implements the DML guard.
- If you build custom kernels, search your kernel tree for the DML2.1 fix in the relevant dml2 source files (for example, dml2_core_dcn4_calcs.c) and verify the guarded arithmetic change exists.
- After installing the updated kernel package, reboot into the patched kernel and reproduce the prior workload that caused the UBSAN trace (if possible) to confirm the warning no longer appears. Vendor advisories emphasize reboot and verification.
Operational guidance — triage, mitigation, and rollout
Immediate steps for administrators
- Prioritize kernel updates on desktops, workstations, and servers that:
- Load the amdgpu driver (lsmod | grep amdgpu).
- Expose DRM device nodes (/dev/dri/*) to non‑trusted users or containers.
- Are part of multi‑tenant hosts, CI runners, or VDI/virtual desktop infrastructures where availability matters.
- If patching is not immediately possible:
- Restrict access to /dev/dri device nodes via udev rules and group permission changes.
- Remove or avoid exposing /dev/dri to untrusted containers (no --device=/dev/dri unless necessary).
- Monitor kernel logs (journalctl -k / dmesg) for UBSAN or amdgpu DML traces similar to the reported stack trace and set alerts.
- Reboot into the patched kernel once updates are installed — the fix is in kernel code and only takes effect after boot.
Medium‑term steps
- Schedule coordinated patch windows for groups of systems that require testing to avoid display regressions (testing on varied hardware topologies is paramount for AMD display changes).
- For embedded or OEM‑supplied devices where vendor kernels lag, open support tickets requesting the backport or an updated firmware/kernel image that includes the upstream commit.
- Reassess device passthrough policies for multi‑tenant CI and cloud fleets: avoid exposing GPU device nodes to untrusted workloads unless necessary.
Why this matters: impact analysis
Strengths of upstream response
- The upstream kernel maintainers and distributors produced a targeted, low‑risk remedy. The change was small and amenable to backports — a preferred pattern for kernel stability.
- Multiple independent vendor trackers and OSV/NVD entries provide consistent descriptions and remediation mappings, making audit and compliance straightforward for operators.
Residual risks and caveats
- Vendor lag is the dominant operational risk: embedded devices, vendor‑fork kernels, and older OEM images can remain vulnerable long after desktop distributions ship fixes.
- Testing is essential: even surgical fixes in display code may reveal regressions on exotic hardware, docking stations, or multi‑monitor topologies; verify on representative hardware before wide rollout.
- Detection blind spots: UBSAN traces are usually produced in kernels built with sanitizers enabled or under specific test harnesses; production kernels rarely run UBSAN, so occurrences in the wild may present as driver warnings, pageflip timeouts, compositor crashes, or hard hangs that are more generic and harder to map back to the arithmetic edge case.
Technical checklist for engineers (highly actionable)
- Inventory:
- 1. Identify hosts with AMD GPU modules: lsmod | grep amdgpu.
- 2. Enumerate /dev/dri permissions and which containers or VMs mount those nodes.
- 3. Record kernel versions (uname -r) and map to distribution advisories for CVE‑2024‑50177.
- Patch:
- 1. Install vendor/distribution kernel updates that include the upstream DML2.1 fix.
- 2. For custom kernels, cherry‑pick the upstream stable commit that guards the exponent calculation in DML2.1, rebuild, and smoke‑test across hardware topologies.
- Validate:
- 1. Reproduce the prior UBSAN trace if you can (staging only) and confirm it no longer occurs.
- 2. Run display workloads for 24–72 hours to catch intermittent regressions with MST/hubs/docks.
- Mitigate:
- 1. Restrict DRM device node access where patching cannot be immediate.
- 2. Remove /dev/dri mounts from CI/untrusted containers until patched.
- 3. Configure logging/alerts for amdgpu warnings, UBSAN messages, and pageflip timeouts.
Broader context for WindowsForum readers
- This CVE is another reminder that modern GPU drivers are complex and that arithmetic or type mismatches — even in math submodules like DML — can produce kernel‑level warnings with real operational consequence.
- Unlike remote code execution bugs, many driver defects manifest as availability problems: freezes, compositor crashes, or system reboots. Those outcomes are operationally serious in multi‑tenant, CI, or VDI environments and therefore deserve rapid attention despite not being high on a confidentiality scale. Vendor advisories consistently emphasize the availability risk for CVE‑2024‑50177 and urge patching.
Critical analysis — strengths and potential risks
Notable strengths
- The fix is small and targeted, limiting regression risk and easing backporting.
- Public disclosures include explicit UBSAN traces and file/line references, allowing maintainers and distributors to target the exact code region during patching and verification.
- Multiple independent vendors and trackers (Ubuntu, SUSE, Debian, OSV/NVD) aligned on severity and recommended actions, improving transparency for administrators.
Potential risks and caveats
- Embedded/OEM long tail: devices with vendor kernels may not receive timely backports and can remain vulnerable for months or years; this is the recurring systemic weakness for kernel driver CVEs.
- Regression risk on uncommon hardware paths: display stack changes must be validated across docking stations, MST hubs, variable monitor firmware, and proprietary firmware paths — something that requires time and representative test inventories.
- Detection and instrumentation limitations: since UBSAN is a developer/debugging tool, many production kernels will not surface the exact UBSAN trace; operators must rely on indirect symptoms (pageflip timeouts, driver resets, compositor logs) to detect potential hits prior to patching.
Conclusion
CVE‑2024‑50177 is a medium‑severity, availability‑oriented vulnerability rooted in an arithmetic corner case inside DML2.1 of the AMD display stack. The fix is surgical and has been integrated into upstream stable kernel branches and distribution packages; the correct operational response is to confirm vendor package mappings, install the patched kernels, and reboot affected hosts. Where immediate patching is not possible, conservative mitigations — restricting access to /dev/dri, avoiding device passthrough to untrusted containers, and increasing kernel log monitoring — will reduce exposure until packages can be applied. The consistency of vendor advisories and the focused nature of the upstream patch make this a straightforward triage and remediation task for most administrators, while the embedded device long tail remains the primary residual risk to manage.- Quick reference: CVE‑ID: CVE‑2024‑50177.
- Primary symptom: UBSAN shift‑out‑of‑bounds in DML2.1 (calculate_cursor_req_attributes/dml core).
- CVSS v3 Base: 5.5 (Medium).
- Remediation: Install distribution/vendor kernel updates that include the DML2.1 guard; reboot.
Source: MSRC Security Update Guide - Microsoft Security Response Center
