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CVE-2024-53071
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CVE-2024-53071
MITRE ATT&CK
Collection
Command and Control
Credential Access
Defense Evasion
Discovery
Execution
Exfiltration
Impact
Initial Access
Lateral Movement
Persistence
Privilege Escalation
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Description
In the Linux kernel, the following vulnerability has been resolved:
drm/panthor: Be stricter about IO mapping flags
The current panthor_device_mmap_io() implementation has two issues:
For mapping DRM_PANTHOR_USER_FLUSH_ID_MMIO_OFFSET,
panthor_device_mmap_io() bails if VM_WRITE is set, but does not clear
VM_MAYWRITE. That means userspace can use mprotect() to make the mapping
writable later on. This is a classic Linux driver gotcha.
I don’t think this actually has any impact in practice:
When the GPU is powered, writes to the FLUSH_ID seem to be ignored; and
when the GPU is not powered, the dummy_latest_flush page provided by the
driver is deliberately designed to not do any flushes, so the only thing
writing to the dummy_latest_flush could achieve would be to make more
flushes happen.panthor_device_mmap_io() does not block MAP_PRIVATE mappings (which are
mappings without the VM_SHARED flag).
MAP_PRIVATE in combination with VM_MAYWRITE indicates that the VMA has
copy-on-write semantics, which for VM_PFNMAP are semi-supported but
fairly cursed.
In particular, in such a mapping, the driver can only install PTEs
during mmap() by calling remap_pfn_range() (because remap_pfn_range()
wants to store the physical address of the mapped physical memory into
the vm_pgoff of the VMA); installing PTEs later on with a fault
handler (as panthor does) is not supported in private mappings, and so
if you try to fault in such a mapping, vmf_insert_pfn_prot() splats when
it hits a BUG() check.
Fix it by clearing the VM_MAYWRITE flag (userspace writing to the FLUSH_ID
doesn’t make sense) and requiring VM_SHARED (copy-on-write semantics for
the FLUSH_ID don’t make sense).
Reproducers for both scenarios are in the notes of my patch on the mailing
list; I tested that these bugs exist on a Rock 5B machine.
Note that I only compile-tested the patch, I haven’t tested it; I don’t
have a working kernel build setup for the test machine yet. Please test it
before applying it.
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