[Xen-changelog] [xen stable-4.2] x86: restrict XEN_DOMCTL_getmemlist

[patchbot@xxxxxxx]

commit d619f1738706224681981b951b5a9cd132adba81
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Nov 27 09:48:27 2013 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Nov 27 09:48:27 2013 +0100

    x86: restrict XEN_DOMCTL_getmemlist
    
    Coverity ID 1055652
    
    (See the code comment.)
    
    This is CVE-2013-4553 / XSA-74.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Reviewed-by: Tim Deegan <tim@xxxxxxx>
    master commit: 19f027cc5daff4a37fd0a28bca2514c721852dd0
    master date: 2013-11-27 09:00:41 +0100
---
 xen/arch/x86/domctl.c |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/xen/arch/x86/domctl.c b/xen/arch/x86/domctl.c
index aa368a6..d5a06fc 100644
--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -385,6 +385,26 @@ long arch_do_domctl(
                 break;
             }
 
+            /*
+             * XSA-74: This sub-hypercall is broken in several ways:
+             * - lock order inversion (p2m locks inside page_alloc_lock)
+             * - no preemption on huge max_pfns input
+             * - not (re-)checking d->is_dying with page_alloc_lock held
+             * - not honoring start_pfn input (which libxc also doesn't set)
+             * Additionally it is rather useless, as the result is stale by
+             * the time the caller gets to look at it.
+             * As it only has a single, non-production consumer (xen-mceinj),
+             * rather than trying to fix it we restrict it for the time being.
+             */
+            if ( /* No nested locks inside copy_to_guest_offset(). */
+                 paging_mode_external(current->domain) ||
+                 /* Arbitrary limit capping processing time. */
+                 max_pfns > GB(4) / PAGE_SIZE )
+            {
+                ret = -EOPNOTSUPP;
+                break;
+            }
+
             spin_lock(&d->page_alloc_lock);
 
             if ( unlikely(d->is_dying) ) {
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.2

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