From 3aab881c7331cf93ffd8d2f2dd9adfd18ed4fc99 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 +++++++++++++ xen/include/xen/config.h | 2 ++ 2 files changed, 15 insertions(+) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index 70bf52f60a..70dfec5af1 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -3781,6 +3781,9 @@ 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; @@ -3838,6 +3841,16 @@ 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); diff --git a/xen/include/xen/config.h b/xen/include/xen/config.h index 7bef8a648d..a3aa1d4832 100644 --- a/xen/include/xen/config.h +++ b/xen/include/xen/config.h @@ -82,6 +82,8 @@ #endif /* !__ASSEMBLY__ */ +#define IS_ALIGNED(val, align) (((val) & ((align) - 1)) == 0) + #define __STR(...) #__VA_ARGS__ #define STR(...) __STR(__VA_ARGS__) -- 2.13.2