[Xen-changelog] [xen stable-4.4] x86/32on64: don't allow recursive page tables from L3

[patchbot@xxxxxxx]

commit fbe0fb4b522a1879a47d80cc7f039c3cb354b636
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Thu Sep 8 14:30:11 2016 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Sep 8 14:30:11 2016 +0200

    x86/32on64: don't allow recursive page tables from L3
    
    L3 entries are special in PAE mode, and hence can't reasonably be used
    for setting up recursive (and hence linear) page table mappings. Since
    abuse is possible when the guest in fact gets run on 4-level page
    tables, this needs to be excluded explicitly.
    
    This is XSA-185 / CVE-2016-7092.
    
    Reported-by: Jérémie Boutoille <jboutoille@xxxxxxxxxxxxxxxxx>
    Reported-by: "æ ¾å°?è?ª(好é£?)" <shangcong.lsc@xxxxxxxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    master commit: c844d637d92a75854ea5c8d4e5ca34302a9f623c
    master date: 2016-09-08 14:14:53 +0200
---
 xen/arch/x86/mm.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 4c12926..591e1bd 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -1011,7 +1011,9 @@ get_page_from_l3e(
 
     rc = get_page_and_type_from_pagenr(
         l3e_get_pfn(l3e), PGT_l2_page_table, d, partial, 1);
-    if ( unlikely(rc == -EINVAL) && get_l3_linear_pagetable(l3e, pfn, d) )
+    if ( unlikely(rc == -EINVAL) &&
+         !is_pv_32bit_domain(d) &&
+         get_l3_linear_pagetable(l3e, pfn, d) )
         rc = 0;
 
     return rc;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.4

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