CVE-2025-38300: Linux Sun8i Ce DMA Fix Tightens Kernel Stability

The Linux kernel fix addressing CVE-2025-38300 corrects two DMA cleanup mistakes inside the sun8i‑ce cipher driver — a technical change that is narrowly scoped and important for device stability, and Microsoft’s public wording that “Azure Linux includes this open‑source library and is therefore potentially affected” should be read as a product‑level inventory attestation, not a categorical statement that no other Microsoft product could carry the same vulnerable kernel code.

Background / Overview​

The vulnerability tracked as CVE‑2025‑38300 lives in the Linux kernel crypto subsystem, in the sun8i‑ce cipher driver. Upstream developers fixed an error‑handling path in the function sun8i_ce_cipher_prepare to stop the driver from attempting to unmap or free DMA addresses it never successfully mapped. The two specific problems corrected are:

• An incorrect unconditional DMA unmap on an error path when dma_map_sg for the destination buffer failed; and
• An attempt to dma_unmap or free an invalid DMA address when dma_map_single for the initialization vector (IV) fails on the IV error path.

The practical result of these bugs was kernel DMA‑API warnings and the potential for instability or oopses on affected systems that load the sun8i‑ce driver. The CVE and its description were recorded across multiple public trackers and distribution advisories shortly after the upstream patch was merged.

What Microsoft actually said (and why that wording matters)​

Microsoft’s Security Response Center (MSRC) entry for this CVE includes a short, factual statement: “Azure Linux includes this open‑source library and is therefore potentially affected.” That phrasing is part of Microsoft’s recent rollout of machine‑readable CSAF/VEX attestations (initially published beginning in October 2025) and reflects the inventory work Microsoft has completed so far for the Azure Linux product family. Microsoft also committed to update CVE/VEX entries if additional Microsoft products are later identified to include the same upstream component.
Why this precision matters: VEX/CSAF attestations are product‑scoped inventory signals. When a vendor says “Product X includes component Y and is therefore potentially affected,” it is telling customers which named product artifacts were checked and found to include the upstream code. It does not by itself assert that every other product the vendor ships has been scanned and is free of the component. Treat the MSRC line as an authoritative, machine‑readable confirmation for Azure Linux — and as a prompt to validate other Microsoft artifacts independently.

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Technical impact of CVE‑2025‑38300​

What the bug does in plain terms​

The sun8i‑ce driver code attempted to unmap DMA mappings without tracking whether those mappings had succeeded. On error paths this can cause:

• DMA‑API warnings logged by the kernel (check_unmap), and
• Potential kernel instability or oops if the DMA unmap subsystem detects inconsistent bookkeeping.

This is primarily a robustness / availability problem rather than an immediate confidentiality or remote code execution risk. The fix is small and defensive: only unmap DMA regions that were mapped successfully; avoid unmapping invalid addresses. Upgrading kernels or applying vendor patches that include the upstream commit cures the defect.

Who is exposed (in general Linux terms)​

Exposure depends on three simple, verifiable facts for each artifact:

• Does the kernel binary include the sun8i‑ce driver (built‑in or as a module)?
• Is the kernel version one that contains the vulnerable commit range (i.e., prior to the upstream fix)?
• Is the driver actually loaded at runtime (module present or built‑in) on the host?

Only hosts whose kernels both include the driver and use an affected commit/version are in scope. For many distributions, the presence of the driver is platform-dependent (embedded SoC images, SBC targets, and vendor kernels are more likely to include sun8i drivers than generic server kernels).

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Is Azure Linux the only Microsoft product that includes the library?​

Short answer: No — not necessarily. Microsoft’s MSRC attestation that Azure Linux includes the implicated open‑source code is an authoritative inventory result for the Azure Linux product family, and Microsoft promises to update the CVE/VEX product mapping should it find additional Microsoft products that ship the same upstream component. That wording means Azure Linux is the only Microsoft product Microsoft has publicly attested as including the component so far, but it is not evidence of absence elsewhere.
Longer, practical explanation:

• Microsoft’s published VEX/CSAF rollout began with Azure Linux (their curated Linux distribution lineage). For that product family Microsoft ran build‑provenance and SBOM/inventory checks and found the upstream driver in the images they ship; hence the statement.
• Large vendors rarely publish a complete, instantaneous mapping of every single binary, kernel, or appliance image across hundreds of SKUs. They typically roll attestations out product by product. Absence of an attestation for another Microsoft product therefore equals “not yet attested,” not “confirmed not present.”
• Other Microsoft artifacts that conceptually could carry the same kernel code include the WSL2 kernel image, various linux‑azure kernel builds, Marketplace/VHD images, managed appliance images, and specialized IoT or embedded builds — any of which might include the sun8i driver depending on targeted hardware and kernel configuration. Whether those artifacts are actually affected requires artifact‑level verification.

In short: Azure Linux = confirmed and attested; other Microsoft products = unknown until inventory/attestation or per‑artifact verification proves otherwise.

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Evidence and independent corroboration​

The technical record for CVE‑2025‑38300 is consistent across multiple independent trackers:

• The NVD entry and distribution trackers summarize the defect and the kernel fix.
• Debian, SUSE, and other distribution security trackers recorded the same description and linked fixes/backports.
• OSV and other vulnerability databases profile the same two DMA‑cleanup error‑path issues and list vendor advisories and patches.

Microsoft’s MSRC wording about Azure Linux being potentially affected matches the operational pattern Microsoft has used in 2025: publish CSAF/VEX attestations starting with Azure Linux, mark the product status, and update mappings if additional Microsoft products are found to ship the affected component. Multiple independent analyses of Microsoft’s approach reach the same interpretation: product‑scoped attestation, not exclusivity.
Where the public record is limited: Microsoft’s MSRC pages sometimes require JavaScript to render and vendors update VEX attestations over time; therefore the most current product mappings may appear in machine‑readable VEX feeds rather than the static narrative text. If you rely on vendor VEX feeds for automation, poll the feed and treat the Azure Linux attestation as a starting point.

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Operational verification steps (artifact‑level checks)​

Security teams and system administrators should verify exposure at the artifact or running‑host level. These steps are practical, short, and deterministic.

• Check the kernel version and build:
• uname -r
• Inspect /boot/config‑$(uname -r) or /proc/config.gz for whether the sun8i‑ce driver is built. Example config lines might be CONFIG_CRYPTO_SUN8I_CE or similar depending on upstream naming.
• Inspect loaded modules and module files:
• lsmod | grep sun8i
• modinfo sun8i_ce_cipher (or check /lib/modules/$(uname -r)/kernel/drivers/crypto/ for the module)
• Search kernel changelogs and vendor advisories for CVE‑2025‑38300 or the upstream commit IDs referenced by OSV/NVD:
• On Debian/Ubuntu: apt changelog linux-image-$(uname -r) | grep -i 38300
• On RPM systems: rpm -q --changelog kernel | grep -i 38300
• For offline images or marketplace VHDs: extract the vmlinuz/initramfs and check module lists or kernel config embedded in the image; many cloud images include /boot/config files.
• For WSL2: if you use the Microsoft‑published WSL kernel, check the WSL kernel config or the WSL kernel release notes for mention of the sun8i driver; custom WSL kernels should be inspected the same way as other kernels.

If any check shows the driver is present and the kernel version predates the fix, treat the host as in‑scope and prioritize remediation.

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Remediation, mitigation, and prioritization​

• Apply vendor kernel updates: upgrade to a kernel or packaged kernel image that includes the upstream fix, or install the vendor backport. This is the definitive fix.
• If kernel update is not immediately possible, consider temporary mitigations: prevent loading the driver (blacklist the module) where feasible, or restrict access to devices that would exercise the driver. Note that blacklisting may not be acceptable for platforms that rely on the driver for required hardware function.
• In multi‑tenant or managed environments, prioritize hosts that run hardware or images targeting Allwinner/Allwinner-derived SoCs because sun8i drivers target Allwinner SoCs. Generic x86 server kernels are less likely to include the driver unless intentionally built for those SoC targets.

Recommended prioritization order:

• Azure Linux images and VMs (confirmed attested by MSRC).
• Custom device images / embedded appliances that target Allwinner SoCs, single‑board computers (SBCs), or vendor distributions for those platforms.
• WSL2 kernels and other Microsoft-supplied kernel artifacts — verify these artifacts specifically rather than assuming they are unaffected.

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Practical detection queries and automation hints​

• Automated inventory: ingest Microsoft’s CSAF/VEX attestation feed (when available) into your vulnerability management or orchestration system and correlate with your asset inventory to find azure linux instances quickly. Microsoft’s attestation is machine‑readable and intended for this purpose.
• Runtime detection: look for kernel DMA warnings in syslog/journal (check_unmap or DMA‑API messages mentioning sun8i). On affected hosts you may see the kernel DMA debug stacktrace referenced in the upstream commit notes.
• Build reproducibility: for images you build or accept from vendors, require SBOMs, kernel config files, and module lists as part of image acceptance so you can quickly determine which images need patching.

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Risks, strengths, and transparency assessment​

Strengths​

• The upstream fix is small, targeted, and straightforward — a defensive cleanup on error paths. That means vendor backports are typically easy to produce and low‑risk to deploy.
• Microsoft’s decision to publish machine‑readable CSAF/VEX attestations, starting with Azure Linux, increases transparency and helps automation for customers who consume those attestations. When you run Azure Linux, Microsoft’s statement is an authoritative signal you can automate against.

Risks and caveats​

• The main operational risk is assumed coverage: teams might mistake the Azure Linux attestation as a blanket guarantee that no other Microsoft product is affected. That would be an unsafe assumption. Microsoft’s wording explicitly says it will update the CVE if additional products are found to include the component — which implies the current mapping is not exhaustive.
• For large estates with mixed images (Azure VM images, Marketplace images, WSL hosts, container base images, appliance images), the real work is artifact‑level verification. Kernel inclusion is an artifact property determined by kernel configuration, packaging, and versioning, so each image should be checked or verified using SBOM/VEX signals.
• Some vendor pages and machine‑readable feeds evolve after initial disclosure. Don’t rely on a single snapshot — poll vendor VEX feeds and distribution trackers for updates.

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Practical checklist for Microsoft customers and admins​

• Treat Microsoft’s Azure Linux attestation as an authoritative “yes” for that product family and patch Azure Linux images promptly.
• For all other Microsoft‑provided artifacts (WSL kernels, Marketplace images, linux‑azure builds), perform the artifact checks outlined above; do not assume absence.
• Automate the ingestion of MSRC CSAF/VEX outputs into your vulnerability automation tooling and correlate with your inventory to detect any newly attested products quickly.
• If you operate heterogeneous environments, allocate patch windows based on exposure: start with confirmed attested images and then move to images that your artifact verification shows carry the driver.

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Conclusion​

CVE‑2025‑38300 is a clear, narrowly scoped kernel robustness fix that corrects improper DMA unmap/free operations in the sun8i‑ce cipher driver. Microsoft’s public statement that “Azure Linux includes this open‑source library and is therefore potentially affected” is a valuable, machine‑readable attestation that Azure Linux customers should treat as authoritative and act on. However, that statement is a product‑level inventory result, not a universal guarantee that other Microsoft products cannot include the same upstream code; other Microsoft‑distributed kernel artifacts may or may not include the driver depending on build configuration and kernel version. Operators should therefore perform per‑artifact verification (kernel config/module checks, kernel changelogs, and SBOM/VEX correlation) and prioritize patching accordingly. The technical fix is straightforward and backportable; the operational challenge is comprehensive artifact inventory and disciplined patching across all images and kernels you run. Treat Microsoft’s Azure Linux attestation as a reliable signal — and use it to focus immediate remediation work while continuing to verify the remainder of your estate.

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Source: MSRC Security Update Guide - Microsoft Security Response Center