| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2024-40950: mm: huge_memory: fix misused mapping_large_folio_support() for anon folios |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| mm: huge_memory: fix misused mapping_large_folio_support() for anon folios |
| |
| When I did a large folios split test, a WARNING "[ 5059.122759][ T166] |
| Cannot split file folio to non-0 order" was triggered. But the test cases |
| are only for anonmous folios. while mapping_large_folio_support() is only |
| reasonable for page cache folios. |
| |
| In split_huge_page_to_list_to_order(), the folio passed to |
| mapping_large_folio_support() maybe anonmous folio. The folio_test_anon() |
| check is missing. So the split of the anonmous THP is failed. This is |
| also the same for shmem_mapping(). We'd better add a check for both. But |
| the shmem_mapping() in __split_huge_page() is not involved, as for |
| anonmous folios, the end parameter is set to -1, so (head[i].index >= end) |
| is always false. shmem_mapping() is not called. |
| |
| Also add a VM_WARN_ON_ONCE() in mapping_large_folio_support() for anon |
| mapping, So we can detect the wrong use more easily. |
| |
| THP folios maybe exist in the pagecache even the file system doesn't |
| support large folio, it is because when CONFIG_TRANSPARENT_HUGEPAGE is |
| enabled, khugepaged will try to collapse read-only file-backed pages to |
| THP. But the mapping does not actually support multi order large folios |
| properly. |
| |
| Using /sys/kernel/debug/split_huge_pages to verify this, with this patch, |
| large anon THP is successfully split and the warning is ceased. |
| |
| The Linux kernel CVE team has assigned CVE-2024-40950 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 6.9 with commit c010d47f107f609b9f4d6a103b6dfc53889049e9 and fixed in 6.9.7 with commit 5df493a99fcf887133cf01d23cd4bebb6d385d3c |
| Issue introduced in 6.9 with commit c010d47f107f609b9f4d6a103b6dfc53889049e9 and fixed in 6.10 with commit 6a50c9b512f7734bc356f4bd47885a6f7c98491a |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2024-40950 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| include/linux/pagemap.h |
| mm/huge_memory.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/5df493a99fcf887133cf01d23cd4bebb6d385d3c |
| https://git.kernel.org/stable/c/6a50c9b512f7734bc356f4bd47885a6f7c98491a |
