From: Ian Jackson Date: Wed, 14 Nov 2012 11:42:21 +0000 (+0000) Subject: xen/mm/shadow: check toplevel pagetables are present before unhooking them. X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~7654 X-Git-Url: https://dgit.raspbian.org/%22http:/www.example.com/cgi/%22https:/%22bookmarks://%22Dat/%22http:/www.example.com/cgi/%22https:/%22bookmarks:/%22Dat?a=commitdiff_plain;h=52c1374d7fc35cd275ced4daf7101d713d7ec294;p=xen.git 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 --- diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c index 39cb7de232..4967da1d35 100644 --- a/xen/arch/x86/mm/shadow/multi.c +++ b/xen/arch/x86/mm/shadow/multi.c @@ -4478,8 +4478,12 @@ static void sh_pagetable_dying(struct vcpu *v, paddr_t gpa) unsigned long gfn; mfn_t smfn, gmfn; - 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 */