[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen stable-4.11] x86/mm: Adjust linear uses / entries when a page loses validation
commit 0eb99bf90b64737c5ba6adaa46951127dcf150cc Author: George Dunlap <george.dunlap@xxxxxxxxxx> AuthorDate: Mon Nov 25 16:26:42 2019 +0100 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Mon Nov 25 16:26:42 2019 +0100 x86/mm: Adjust linear uses / entries when a page loses validation "Linear pagetables" is a technique which involves either pointing a pagetable at itself, or to another pagetable the same or higher level. Xen has limited support for linear pagetables: A page may either point to itself, or point to another page of the same level (i.e., L2 to L2, L3 to L3, and so on). XSA-240 introduced an additional restriction that limited the "depth" of such chains by allowing pages to either *point to* other pages of the same level, or *be pointed to* by other pages of the same level, but not both. To implement this, we keep track of the number of outstanding times a page points to or is pointed to another page table, to prevent both from happening at the same time. Additionally, XSA-299 introduced a mode whereby if a page was known to have been only partially validated, _put_page_type() would be called with PTF_partial_set, indicating that if the page had been de-validated by someone else, the type count should be left alone. Unfortunately, this change did not account for the required accounting for linear page table uses and entries; in the case that a previously partially-devalidated pagetable was fully-devalidated by someone else, the linear_pt_counts are not updated. This could happen in one of two places: 1. In the case a partially-devalidated page was re-validated by someone else 2. During domain tear-down, when pages are force-invalidated while leaving the type count intact. The second could be ignored, since at that point the pages can no longer be abused; but the first requires handling. Note however that this would not be a security issue: having the counts be too high is overly strict (i.e., will prevent a page from being used in a way which is perfectly safe), but shouldn't cause any other issues. Fix this by adjusting the linear counts when a page loses validation, regardless of whether the de-validation completed or was only partial. Signed-off-by: George Dunlap <george.dunlap@xxxxxxxxxx> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> master commit: 77beba7c921a286c31a2a76f26500047f353614a master date: 2019-11-25 10:58:27 +0000 --- xen/arch/x86/mm.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index f46f05d3cc..82d7707fc2 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -2763,14 +2763,17 @@ static int _put_final_page_type(struct page_info *page, unsigned long type, { int rc = free_page_type(page, type, preemptible); + if ( ptpg && PGT_type_equal(type, ptpg->u.inuse.type_info) && + (type & PGT_validated) && rc != -EINTR ) + { + /* Any time we begin de-validation of a page, adjust linear counts */ + dec_linear_uses(page); + dec_linear_entries(ptpg); + } + /* No need for atomic update of type_info here: noone else updates it. */ if ( rc == 0 ) { - if ( ptpg && PGT_type_equal(type, ptpg->u.inuse.type_info) ) - { - dec_linear_uses(page); - dec_linear_entries(ptpg); - } ASSERT(!page->linear_pt_count || page_get_owner(page)->is_dying); set_tlbflush_timestamp(page); smp_wmb(); -- generated by git-patchbot for /home/xen/git/xen.git#stable-4.11 _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/xen-changelog
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