From e201bce9a19d158ee979ed9a6690cfeede925c1f Mon Sep 17 00:00:00 2001 From: Ian Jackson Date: Wed, 14 Nov 2012 11:44:46 +0000 Subject: xen/mm/shadow: check toplevel pagetables are present before unhooking them. If the guest has not fully populated its top-level PAE entries when it calls HVMOP_pagetable_dying, the shadow code could try to unhook entries from MFN 0. Add a check to avoid that case. This issue was introduced by c/s 21239:b9d2db109cf5. This is a security problem, XSA-23 / CVE-2012-4538. Signed-off-by: Tim Deegan Tested-by: Andrew Cooper Acked-by: Ian Campbell Committed-by: Ian Jackson xen-4.1-testing changeset: 23409:61eb3d030f52 Backport-requested-by: security@xen.org Committed-by: Ian Jackson --- xen/arch/x86/mm/shadow/multi.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c index ca7635b416..243b9f4d44 100644 --- a/xen/arch/x86/mm/shadow/multi.c +++ b/xen/arch/x86/mm/shadow/multi.c @@ -4698,8 +4698,12 @@ static void sh_pagetable_dying(struct vcpu *v, paddr_t gpa) } for ( i = 0; i < 4; i++ ) { - if ( fast_path ) - smfn = _mfn(pagetable_get_pfn(v->arch.shadow_table[i])); + if ( fast_path ) { + if ( pagetable_is_null(v->arch.shadow_table[i]) ) + smfn = _mfn(INVALID_MFN); + else + smfn = _mfn(pagetable_get_pfn(v->arch.shadow_table[i])); + } else { /* retrieving the l2s */ -- cgit v1.2.3