- 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: 1. 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. 2. 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.
- Source
- 416baaa9-dc9f-4396-8d5f-8c081fb06d67
- NVD status
- Analyzed
CVSS 3.1
- Type
- Primary
- Base score
- 5.5
- Impact score
- 3.6
- Exploitability score
- 1.8
- Vector string
- CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- Severity
- MEDIUM
- Hype score
- Not currently trending
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