CVE-2025-21939 drm/xe/hmm: Don't dereference struct page pointers without notifier lock
A null pointer dereference in the Linux kernel's Xe GPU driver can cause a system crash when accessing page structures without proper locking.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-21939?
CVE-2025-21939 is a high-severity vulnerability in Linux kernel, published on 1 Apr 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
drm/xe/hmm: Don't dereference struct page pointers without notifier lock
The pnfs that we obtain from hmm_range_fault() point to pages that we don't have a reference on, and the guarantee that they are still in the cpu page-tables is that the notifier lock must be held and the notifier seqno is still valid.
So while building the sg table and marking the pages accesses / dirty we need to hold this lock with a validated seqno.
However, the lock is reclaim tainted which makes sg_alloc_table_from_pages_segment() unusable, since it internally allocates memory.
Instead build the sg-table manually. For the non-iommu case this might lead to fewer coalesces, but if that's a problem it can be fixed up later in the resource cursor code. For the iommu case, the whole sg-table may still be coalesced to a single contigous device va region.
This avoids marking pages that we don't own dirty and accessed, and it also avoid dereferencing struct pages that we don't own.
v2: - Use assert to check whether hmm pfns are valid (Matthew Auld) - Take into account that large pages may cross range boundaries (Matthew Auld)
v3: - Don't unnecessarily check for a non-freed sg-table. (Matthew Auld) - Add a missing up_read() in an error path. (Matthew Auld)
(cherry picked from commit ea3e66d280ce2576664a862693d1da8fd324c317)
Weakness: CWE-476
Which versions are affected by CVE-2025-21939?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21939?
Apply the vendor's patch.
Is CVE-2025-21939 being exploited?
There is no known exploitation of CVE-2025-21939 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21939, DEBIAN-CVE-2025-21939, GHSA-5jw6-g45h-9h97, UBUNTU-CVE-2025-21939.