ghsa-42c7-w7r7-3v3m
Vulnerability from github
Published
2024-11-19 18:31
Modified
2024-11-27 00:31
Severity ?
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Details

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.

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{
  "affected": [],
  "aliases": [
    "CVE-2024-53071"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2024-11-19T18:15:26Z",
    "severity": "MODERATE"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ndrm/panthor: Be stricter about IO mapping flags\n\nThe current panthor_device_mmap_io() implementation has two issues:\n\n1. For mapping DRM_PANTHOR_USER_FLUSH_ID_MMIO_OFFSET,\n   panthor_device_mmap_io() bails if VM_WRITE is set, but does not clear\n   VM_MAYWRITE. That means userspace can use mprotect() to make the mapping\n   writable later on. This is a classic Linux driver gotcha.\n   I don\u0027t think this actually has any impact in practice:\n   When the GPU is powered, writes to the FLUSH_ID seem to be ignored; and\n   when the GPU is not powered, the dummy_latest_flush page provided by the\n   driver is deliberately designed to not do any flushes, so the only thing\n   writing to the dummy_latest_flush could achieve would be to make *more*\n   flushes happen.\n\n2. panthor_device_mmap_io() does not block MAP_PRIVATE mappings (which are\n   mappings without the VM_SHARED flag).\n   MAP_PRIVATE in combination with VM_MAYWRITE indicates that the VMA has\n   copy-on-write semantics, which for VM_PFNMAP are semi-supported but\n   fairly cursed.\n   In particular, in such a mapping, the driver can only install PTEs\n   during mmap() by calling remap_pfn_range() (because remap_pfn_range()\n   wants to **store the physical address of the mapped physical memory into\n   the vm_pgoff of the VMA**); installing PTEs later on with a fault\n   handler (as panthor does) is not supported in private mappings, and so\n   if you try to fault in such a mapping, vmf_insert_pfn_prot() splats when\n   it hits a BUG() check.\n\nFix it by clearing the VM_MAYWRITE flag (userspace writing to the FLUSH_ID\ndoesn\u0027t make sense) and requiring VM_SHARED (copy-on-write semantics for\nthe FLUSH_ID don\u0027t make sense).\n\nReproducers for both scenarios are in the notes of my patch on the mailing\nlist; I tested that these bugs exist on a Rock 5B machine.\n\nNote that I only compile-tested the patch, I haven\u0027t tested it; I don\u0027t\nhave a working kernel build setup for the test machine yet. Please test it\nbefore applying it.",
  "id": "GHSA-42c7-w7r7-3v3m",
  "modified": "2024-11-27T00:31:41Z",
  "published": "2024-11-19T18:31:07Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2024-53071"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2604afd65043e8f9d4be036cb1242adf6b5723cf"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f432a1621f049bb207e78363d9d0e3c6fa2da5db"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}


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