[PATCH 3.19.y-ckt 53/66] x86/mm/xen: Suppress hugetlbfs in PV guests

[Kamal Mostafa]

3.19.8-ckt20 -stable review patch.  If anyone has any objections, please let me know.

---8<------------------------------------------------------------

From: Jan Beulich <JBeulich at suse.com>

commit 103f6112f253017d7062cd74d17f4a514ed4485c upstream.

Huge pages are not normally available to PV guests. Not suppressing
hugetlbfs use results in an endless loop of page faults when user mode
code tries to access a hugetlbfs mapped area (since the hypervisor
denies such PTEs to be created, but error indications can't be
propagated out of xen_set_pte_at(), just like for various of its
siblings), and - once killed in an oops like this:

  kernel BUG at .../fs/hugetlbfs/inode.c:428!
  invalid opcode: 0000 [#1] SMP
  ...
  RIP: e030:[<ffffffff811c333b>]  [<ffffffff811c333b>] remove_inode_hugepages+0x25b/0x320
  ...
  Call Trace:
   [<ffffffff811c3415>] hugetlbfs_evict_inode+0x15/0x40
   [<ffffffff81167b3d>] evict+0xbd/0x1b0
   [<ffffffff8116514a>] __dentry_kill+0x19a/0x1f0
   [<ffffffff81165b0e>] dput+0x1fe/0x220
   [<ffffffff81150535>] __fput+0x155/0x200
   [<ffffffff81079fc0>] task_work_run+0x60/0xa0
   [<ffffffff81063510>] do_exit+0x160/0x400
   [<ffffffff810637eb>] do_group_exit+0x3b/0xa0
   [<ffffffff8106e8bd>] get_signal+0x1ed/0x470
   [<ffffffff8100f854>] do_signal+0x14/0x110
   [<ffffffff810030e9>] prepare_exit_to_usermode+0xe9/0xf0
   [<ffffffff814178a5>] retint_user+0x8/0x13

This is CVE-2016-3961 / XSA-174.

Reported-by: Vitaly Kuznetsov <vkuznets at redhat.com>
Signed-off-by: Jan Beulich <jbeulich at suse.com>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Andy Lutomirski <luto at amacapital.net>
Cc: Boris Ostrovsky <boris.ostrovsky at oracle.com>
Cc: Borislav Petkov <bp at alien8.de>
Cc: Brian Gerst <brgerst at gmail.com>
Cc: David Vrabel <david.vrabel at citrix.com>
Cc: Denys Vlasenko <dvlasenk at redhat.com>
Cc: H. Peter Anvin <hpa at zytor.com>
Cc: Juergen Gross <JGross at suse.com>
Cc: Linus Torvalds <torvalds at linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof at suse.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Thomas Gleixner <tglx at linutronix.de>
Cc: Toshi Kani <toshi.kani at hp.com>
Cc: xen-devel <xen-devel at lists.xenproject.org>
Link: http://lkml.kernel.org/r/57188ED802000078000E431C@prv-mh.provo.novell.com
Signed-off-by: Ingo Molnar <mingo at kernel.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 arch/x86/include/asm/hugetlb.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
index 68c0539..7aadd3c 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -4,6 +4,7 @@
 #include <asm/page.h>
 #include <asm-generic/hugetlb.h>
 
+#define hugepages_supported() cpu_has_pse
 
 static inline int is_hugepage_only_range(struct mm_struct *mm,
 					 unsigned long addr,
-- 
2.7.4