UBUNTU-CVE-2025-38563
In the Linux kernel, the following vulnerability has been resolved: perf/core: Prevent VMA split of buffer mappings The perf mmap code is careful about mmap()'ing the user page with the ringbuffer and additionally the auxiliary buffer, when the event supports it. Once the first mapping is established, subsequent mapping have to use the same offset and the same size in both cases. The reference counting for the ringbuffer and the auxiliary buffer depends on this being correct. Though perf does not prevent that a related mapping is split via mmap(2), munmap(2) or mremap(2). A split of a VMA results in perf_mmap_open() calls, which take reference counts, but then the subsequent perf_mmap_close() calls are not longer fulfilling the offset and size checks. This leads to reference count leaks. As perf already has the requirement for subsequent mappings to match the initial mapping, the obvious consequence is that VMA splits, caused by resizing of a mapping or partial unmapping, have to be prevented. Implement the vm_operations_struct::may_split() callback and return unconditionally -EINVAL. That ensures that the mapping offsets and sizes cannot be changed after the fact. Remapping to a different fixed address with the same size is still possible as it takes the references for the new mapping and drops those of the old mapping.
02 / AFFECTED SOFTWARE
Affected packages
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42 explicit affected versions
67 explicit affected versions
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1 explicit affected versions
1 explicit affected versions
76 explicit affected versions
119 explicit affected versions
5 explicit affected versions
10 explicit affected versions
8 explicit affected versions
78 explicit affected versions
11 explicit affected versions
1 explicit affected versions
69 explicit affected versions
123 explicit affected versions
41 explicit affected versions
66 explicit affected versions
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
In the Linux kernel, the following vulnerability has been resolved: perf/core: Prevent VMA split of buffer mappings The perf mmap code is careful about mmap()'ing the user page with the ringbuffer and additionally the auxiliary buffer, when the event supports it. Once the first mapping is established, subsequent mapping have to use the same offset and the same size in both cases. The reference counting for the ringbuffer and the auxiliary buffer depends on this being correct. Though perf does not prevent that a related mapping is split via mmap(2), munmap(2) or mremap(2). A split of a VMA results in perf_mmap_open() calls, which take reference counts, but then the subsequent perf_mmap_close() calls are not longer fulfilling the offset and size checks. This leads to reference count leaks. As perf already has the requirement for subsequent mappings to match the initial mapping, the obvious consequence is that VMA splits, caused by resizing of a mapping or partial unmapping, have to be prevented. Implement the vm_operations_struct::may_split() callback and return unconditionally -EINVAL. That ensures that the mapping offsets and sizes cannot be changed after the fact. Remapping to a different fixed address with the same size is still possible as it takes the references for the new mapping and drops those of the old mapping.
05 / REFERENCES
Further evidence
- https://git.kernel.org/linus/b024d7b56c77191cde544f838debb7f8451cd0d6
- https://git.kernel.org/stable/c/65311aad4c808bedad0c05d9bb8b06c47dae73eb
- https://git.kernel.org/stable/c/6757a31a8e295ae4f01717a954afda173f25a121
- https://git.kernel.org/stable/c/7b84cb58d1f0aa07656802eae24689566e5f5b1b
- https://git.kernel.org/stable/c/b024d7b56c77191cde544f838debb7f8451cd0d6
- https://git.kernel.org/stable/c/e529888b7e8092912dd8789bdfc76685ccd2ff5f
- https://git.kernel.org/stable/c/ff668930871e0198c7f4e325058b8b7c286787bd
- https://ubuntu.com/security/CVE-2025-38563
- https://ubuntu.com/security/notices/USN-7879-1
- https://ubuntu.com/security/notices/USN-7879-2
- https://ubuntu.com/security/notices/USN-7879-3
- https://ubuntu.com/security/notices/USN-7879-4
- https://ubuntu.com/security/notices/USN-7880-1
- https://ubuntu.com/security/notices/USN-7909-1
- https://ubuntu.com/security/notices/USN-7909-2
- https://ubuntu.com/security/notices/USN-7909-3
- https://ubuntu.com/security/notices/USN-7909-4
- https://ubuntu.com/security/notices/USN-7909-5
- https://ubuntu.com/security/notices/USN-7910-1
- https://ubuntu.com/security/notices/USN-7910-2
- https://ubuntu.com/security/notices/USN-7933-1
- https://ubuntu.com/security/notices/USN-7934-1
- https://ubuntu.com/security/notices/USN-7938-1
- https://www.cve.org/CVERecord?id=CVE-2025-38563