In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
x86\/mm\/pat: Acquire init_mm write lock on collapse to avoid UAF<\/p>\n
x86 implements page attribute modification using its Change Page
\nAttributes (CPA) mechanism.<\/p>\n
This tracks properties of ranges such as cache mode through x86 page
\nattributes, and as part of that logic manipulates kernel page tables.<\/p>\n
Since commit:<\/p>\n
41d88484c71c (“x86\/mm\/pat: restore large ROX pages after fragmentation”)<\/p>\n
ranges of kernel page table entries can be collapsed into
\nhuge page table entries as part of this logic.<\/p>\n
As part of this collapse, it frees the page tables which the collapsed
\nentries previously pointed to, and it does so without any relevant locks
\nbeing held to preclude concurrent kernel page table walkers.<\/p>\n
The only way this code can be reached is if CPA_COLLAPSE is specified, and
\nthis is only set in set_memory_rox() via:<\/p>\n
set_memory_rox()
\n-> change_page_attr_set_clr()
\n-> cpa_flush()
\n-> cpa_collapse_large_pages()<\/p>\n
Notable users of this are execmem and BPF when manipulating executable
\nmappings.<\/p>\n
However, this is problematic for ptdump as it walks ranges it does not own
\nand thus runs the risk of a use-after-free on page tables freed underneath
\nit.<\/p>\n
In addition, concurrent CPA collapse operations are possible which can also
\ncause races.<\/p>\n
Resolve the issue by acquiring the mmap write lock on init_mm across the
\nwhole operation.<\/p>\n
It is safe to acquire a sleeping lock as all the callers invoke
\nset_memory_rox() from process context and in any case,
\nchange_page_attr_set_clr() calls vm_unmap_alias() which ultimately takes a
\nmutex, disallowing atomic context here.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
x86\/mm\/pat: Acquire init_mm write lock on collapse to avoid UAF<\/p>\n
x86 implements page attribute modification using its Change Page
\nA<\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-29099","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/29099","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=29099"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=29099"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=29099"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}