A newly tracked vulnerability, CVE-2024-53116, has emerged in the Linux kernel's DRM subsystem, specifically impacting the panthor GPU driver. This flaw could cause unexpected kernel warnings and potentially trigger system instability or denial of service in systems using the panthor driver for GPU acceleration. In this post, we break down what happened, how it was fixed, show key code snippets, and detail how you might trigger or recognize this vulnerability. All content here is exclusive, simplified, and intended for both admins and developers.

What Is CVE-2024-53116?

CVE-2024-53116 is a bug relating to how the panthor Direct Rendering Manager handles *partial mappings* of buffer objects (BOs) to the GPU. The bug occurs if a mapped memory region spans more than one scatterlist entry, and the mapping *offset* does not point to the first page in the starting scatterlist. Here, the offset variable wasn’t reset after the first scatterlist was done, causing operations on the wrong memory range.

The result is kernel warnings like these

WARNING: CPU: 1 PID: 650 at drivers/iommu/io-pgtable-arm.c:659 __arm_lpae_unmap+x254/x5a
...
panthor : [drm] drm_WARN_ON(unmapped_sz != pgsize * pgcount)
WARNING: CPU: 1 PID: 650 at drivers/gpu/drm/panthor/panthor_mmu.c:922 panthor_vm_unmap_pages+x124/x1c8 [panthor]

This can lead to failed unmapping operations, potential memory issues, and system instability.

Why Does It Happen? (Technical Details)

The DRM subsystem uses scatter-gather lists (scatterlists) for efficient memory mapping. If you only want to map part of a buffer—say, not starting at the very beginning—a calculation needs to figure out which page to start, skip the right offset, and ensure the partial mapping covers the right pages. The bug: after stepping into the second (or further) scatterlist entry, the *offset* was not cleared, so the memory range got miscalculated.

If exploited in a specific way (deliberately sending custom IOCTLs with crafted buffer mapping requests), this could create unexpected behavior in systems doing GPU compute or graphics with the panthor driver.

If your system is hit by this bug, you might see logs similar to

WARNING: CPU: 1 PID: 650 at drivers/iommu/io-pgtable-arm.c:659 __arm_lpae_unmap+x254/x5a
...
panthor : [drm] *ERROR* failed to unmap range ffffa388f000-ffffa389000 (requested range ffffa388c000-ffffa389000)

This hints at a remapping or unmapping operation that mismatched memory boundaries by not properly correcting for the offset.

A demonstration (Python pseudocode for concept)

import fcntl
import struct

# These values require a custom IOCTL code and understanding of panthor's UAPI
VHARD_IOCTL_MAP = x1234  # Example value
buffer_fd = open('/dev/dri/card','rb+')

# Setup your buffer object with unaligned offset and crafted length
mapping = struct.pack('III', BO_HANDLE, OFFSET_NOT_ZERO, LENGTH_MULTIPLE_PAGES)
fcntl.ioctl(buffer_fd, VHARD_IOCTL_MAP, mapping)

Modifying these parameters could provoke the flaw, though real exploitability may be limited to causing kernel warnings and system instability (DoS), not code execution.

From the official commit, patching goes as follows

// Before: (buggy usage)
if (offset) {
    to_map = min(pgsize - offset, size);
    ...
    offset += to_map;
} else {
    to_map = min(pgsize, size);
}

// Missing: reset offset after leaving the initial scatterlist

// After: corrected logic
if (offset) {
    to_map = min(pgsize - offset, size);
    offset = ; // Reset offset for subsequent scatterlist entries
} else {
    to_map = min(pgsize, size);
}

Key Point:
*After* the first chunk of the mapping, offset must always be zero for the next scatterlist in the chain. Forgetting this results in skewed mappings and eventual errors or system warnings.

References & Further Reading

- Upstream Kernel Commit (lore.kernel.org)
- Linux Patch: drm/panthor: Fix handling of partial GPU mapping of BOs
- CVE Record – CVE-2024-53116 (cve.org) *(once published)*

Severity:

Medium – Can cause instability, kernel warnings, or DoS when triggered. No evidence of privilege escalation or remote exploit.

Summary

CVE-2024-53116 highlights the subtlety of low-level driver bugs—especially in complex GPU memory mapping code. Any error in managing partial mappings and offsets can cascade into kernel errors. While this bug’s main risk is system stability, it's a reminder of how small mistakes can have significant effects in kernel space. Update your panthor drivers and kernels!

If you want a deeper dive, check the original patch:
https://patchwork.kernel.org/project/dri-devel/patch/20240608-drm-panthor-partial-mapping-fix-v1-1-13d1c85f6bc7@kernel.org/


*Feel free to share or comment below if you spot this in the wild or have insight into panthor or DRM evolving security!*

Timeline

Published on: 12/02/2024 14:15:12 UTC
Last modified on: 12/19/2024 09:39:33 UTC