In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm\/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()<\/p>\n
copy_hugetlb_page_range() clears the uffd-wp bit of migration and hwpoison
\nentries with huge_pte_clear_uffd_wp(), which operates on the present-PTE
\nbit position. Swap entries keep the uffd-wp state elsewhere — the
\nmigration branch reads and sets it with pte_swp_uffd_wp() and
\npte_swp_mkuffd_wp() — and the present-PTE position falls into the swap
\npayload. On x86-64 it lands in the inverted swap offset, where a
\nnaturally-aligned hugetlb PFN always has the affected bit set, so the
\nclear advances the encoded PFN by two pages.<\/p>\n
No userfaultfd needs to be involved: the clear is guarded only by the
\nchild VMA not being uffd-wp registered, so a plain fork() with an
\nin-flight hugetlb migration entry (or a poisoned hugetlb page) corrupts
\nthe entry copied into the child. Instrumenting the clear and forking
\nafter MADV_HWPOISON on a 2MB anon hugetlb page shows:<\/p>\n
offset before=120e00
\n offset after =120e02<\/p>\n
The fallout is mostly latent: rmap walks match migration entries by folio
\nrange and remove_migration_pte() rebuilds the PTE from the folio, so a
\nwithin-folio PFN skew heals once migration completes. But any path that
\nre-encodes the corrupted offset — e.g. hugetlb_change_protection()
\nrewriting a writable migration entry via
\nmake_readable_migration_entry(swp_offset(entry)) — propagates it.<\/p>\n
Migration entries legitimately carry uffd-wp, so clear it with
\npte_swp_clear_uffd_wp(), matching copy_nonpresent_pte() and
\nmove_huge_pte().<\/p>\n
A hwpoison entry, on the other hand, never carries the uffd-wp bit: it is
\ninstalled fresh by make_hwpoison_entry() (try_to_unmap_one() does not
\npreserve uffd-wp on the hwpoison path) and hugetlb_change_protection()
\nleaves hwpoison entries untouched. There was nothing to clear there, only
\nthe corruption, so drop the clear entirely.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
mm\/hugetlb: fix swap entry corruption when clearing uffd-wp at fork()<\/p>\n
copy_hugetlb_page_range() clears the uffd-wp bit of migratio<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-17473","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/17473","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln"}],"about":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/types\/vuln"}],"wp:attachment":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=17473"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=17473"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=17473"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}