From fa7268b94f8a0a7792ee12d5b8e23a60e52a3a84 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Tue, 20 Jun 2017 19:18:54 +0100 Subject: [PATCH] x86/grant: Disallow misaligned PTEs Pagetable entries must be aligned to function correctly. Disallow attempts from the guest to have a grant PTE created at a misaligned address, which would result in corruption of the L1 table with largely-guest-controlled values. This is XSA-227 Signed-off-by: Andrew Cooper Reviewed-by: Jan Beulich --- xen/arch/x86/mm.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 97b3b4b..00f517a 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -3763,6 +3763,9 @@ static int create_grant_pte_mapping( l1_pgentry_t ol1e; struct domain *d = v->domain; + if ( !IS_ALIGNED(pte_addr, sizeof(nl1e)) ) + return GNTST_general_error; + adjust_guest_l1e(nl1e, d); gmfn = pte_addr >> PAGE_SHIFT; @@ -3819,6 +3822,16 @@ static int destroy_grant_pte_mapping( struct page_info *page; l1_pgentry_t ol1e; + /* + * addr comes from Xen's active_entry tracking so isn't guest controlled, + * but it had still better be PTE-aligned. + */ + if ( !IS_ALIGNED(addr, sizeof(ol1e)) ) + { + ASSERT_UNREACHABLE(); + return GNTST_general_error; + } + gmfn = addr >> PAGE_SHIFT; page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC); -- 2.1.4