From: Ian Jackson Date: Wed, 14 Nov 2012 11:36:02 +0000 (+0000) Subject: x86/physmap: Prevent incorrect updates of m2p mappings X-Git-Tag: archive/raspbian/4.8.0-1+rpi1~1^2~7655 X-Git-Url: https://dgit.raspbian.org/%22http://www.example.com/cgi/%22/%22http:/www.example.com/cgi/%22?a=commitdiff_plain;h=ef3cea268fdff77f93368369c5998b1c975aa297;p=xen.git x86/physmap: Prevent incorrect updates of m2p mappings In certain conditions, such as low memory, set_p2m_entry() can fail. Currently, the p2m and m2p tables will get out of sync because we still update the m2p table after the p2m update has failed. If that happens, subsequent guest-invoked memory operations can cause BUG()s and ASSERT()s to kill Xen. This is fixed by only updating the m2p table iff the p2m was successfully updated. This is a security problem, XSA-22 / CVE-2012-4537. Signed-off-by: Andrew Cooper Acked-by: Ian Campbell Acked-by: Ian Jackson Committed-by: Ian Jackson --- diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c index 9857b5b2de..e35194216c 100644 --- a/xen/arch/x86/mm/p2m.c +++ b/xen/arch/x86/mm/p2m.c @@ -633,7 +633,10 @@ guest_physmap_add_entry(struct domain *d, unsigned long gfn, if ( mfn_valid(_mfn(mfn)) ) { if ( !set_p2m_entry(p2m, gfn, _mfn(mfn), page_order, t, p2m->default_access) ) + { rc = -EINVAL; + goto out; /* Failed to update p2m, bail without updating m2p. */ + } if ( !p2m_is_grant(t) ) { for ( i = 0; i < (1UL << page_order); i++ ) @@ -656,6 +659,7 @@ guest_physmap_add_entry(struct domain *d, unsigned long gfn, } } +out: p2m_unlock(p2m); return rc;