In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
KVM: x86\/mmu: Ensure hugepage is in by slot before checking max mapping level<\/p>\n
When recovering hugepages in the shadow MMU, verify that the base gfn of
\nthe shadow page is actually contained within the target memslot, *before*
\nquerying the max mapping level given the shadow page’s gfn. Failure to
\npre-check the validity of the gfn can lead to an out-of-bounds access to
\nthe slot’s lpage_info (which typically manifests as a host #PF because the
\nlpage_info is vmalloc’d) if the guest creates a hugepage mapping (in its
\nPTEs) that extends “below” the bounds of a memslot.<\/p>\n
When faulting in memory for a guest, and the size of the guest mapping is
\ngreater than KVM’s (current) max mapping, then KVM will create a “direct”
\nshadow page (direct in that there are no gPTEs to shadow, and so the target
\ngfn is a direct calculation given the base gfn of the shadow page). The
\nhugepage recovery flow looks for such direct shadow pages, as forcing 4KiB
\nmappings when dirty logging generates the guest > host mapping size case.
\nWhen the 4KiB restriction is lifted, then KVM can replace the shadow page
\nwith a hugepage.<\/p>\n
But if KVM originally used a smaller mapping than the guest because the
\nrange of memory covered by the guest hugepage exceeds the bounds of a
\nmemslot, then KVM will link a direct shadow page with a gfn that is outside
\nthe bounds of the memslot being used to fault in memory. The rmap entry
\nadded for the leaf mapping is correct and within bounds, but the gfn of the
\nleaf SPTE’s parent shadow page will be out of bounds.<\/p>\n
BUG: unable to handle page fault for address: ffffc90000806ffc
\n #PF: supervisor read access in kernel mode
\n #PF: error_code(0x0000) – not-present page
\n PGD 100000067 P4D 100000067 PUD 1002a7067 PMD 10612f067 PTE 0
\n Oops: Oops: 0000 [#1] SMP
\n CPU: 13 UID: 1000 PID: 757 Comm: mmu_stress_test Not tainted 7.1.0-rc1-48ce1e26eace-x86_pir_to_irr_comments-vm #341 PREEMPT
\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02\/06\/2015
\n RIP: 0010:kvm_mmu_max_mapping_level+0x79\/0x2b0 [kvm]
\n Call Trace:<\/p>\n
kvm_mmu_recover_huge_pages+0x21b\/0x320 [kvm]
\n kvm_set_memslot+0x1ee\/0x590 [kvm]
\n kvm_set_memory_region.part.0+0x3a1\/0x4d0 [kvm]
\n kvm_vm_ioctl+0x9bf\/0x15d0 [kvm]
\n __x64_sys_ioctl+0x8a\/0xd0
\n do_syscall_64+0xb7\/0xbb0
\n entry_SYSCALL_64_after_hwframe+0x4b\/0x53
\n RIP: 0033:0x7f21c0f1a9bf<\/p>\n
Don’t bother pre-checking the bounds of the potential hugepage, i.e. don’t
\ncheck that e.g. sp->gfn + KVM_PAGES_PER_HPAGE(sp->role.level + 1) is also
\nwithin the memslot, as the checks performed by kvm_mmu_max_mapping_level()
\nare a superset of the basic bounds checks. I.e. pre-checking the full
\nrange would be a dubious micro-optimization.<\/p>\n","protected":false},"excerpt":{"rendered":"
In the Linux kernel, the following vulnerability has been resolved:<\/p>\n
KVM: x86\/mmu: Ensure hugepage is in by slot before checking max mapping level<\/p>\n
When recovering hugepages in the shadow MMU, verify <\/p>\n","protected":false},"template":"","meta":[],"categories":[],"tags":[],"class_list":["post-14884","vuln","type-vuln","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.54iter.cn\/index.php?rest_route=\/wp\/v2\/vuln\/14884","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=14884"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=14884"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.54iter.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=14884"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}