[x86] xen: suppress hugetlbfs in PV guests (CVE-2016-3961)

debian/changelog

@@ -1,3 +1,10 @@
+linux (4.5.1-2) UNRELEASED; urgency=medium
+
+  [ Salvatore Bonaccorso ]
+  * [x86] xen: suppress hugetlbfs in PV guests (CVE-2016-3961)
+
+ -- Salvatore Bonaccorso <carnil@debian.org>  Thu, 14 Apr 2016 20:52:28 +0200
+
 linux (4.5.1-1) unstable; urgency=medium
 
   * New upstream stable update:

debian/patches/bugfix/x86/x86-xen-suppress-hugetlbfs-in-PV-guests.patch

@@ -0,0 +1,73 @@
+From: Jan Beulich <jbeulich@suse.com>
+Date: Thu, 14 Apr 2016 20:38:30 +0200
+Subject: x86/xen: suppress hugetlbfs in PV guests
+Origin: http://xenbits.xen.org/xsa/xsa174.patch
+
+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
+Modules linked in: ...
+Supported: Yes
+CPU: 2 PID: 6088 Comm: hugetlbfs Tainted: G        W         4.4.0-2016-01-20-pv #2
+Hardware name: ...
+task: ffff8808059205c0 ti: ffff880803c84000 task.ti: ffff880803c84000
+RIP: e030:[<ffffffff811c333b>]  [<ffffffff811c333b>] remove_inode_hugepages+0x25b/0x320
+RSP: e02b:ffff880803c879a8  EFLAGS: 00010202
+RAX: 000000000077a4db RBX: ffffea001acff000 RCX: 0000000078417d38
+RDX: 0000000000000000 RSI: 000000007e154fa7 RDI: ffff880805d70960
+RBP: 0000000000000960 R08: 0000000000000000 R09: 0000000000000000
+R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
+R13: ffff880807486018 R14: 0000000000000000 R15: ffff880803c87af0
+FS:  00007f85fa8b8700(0000) GS:ffff88080b640000(0000) knlGS:0000000000000000
+CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
+CR2: 00007f85fa000000 CR3: 0000000001a0a000 CR4: 0000000000040660
+Stack:
+ ffff880000000fb0 ffff880803c87a18 ffff880803c87ae8 ffff8808059205c0
+ ffff880803c87af0 ffff880803c87ae8 ffff880807486018 0000000000000000
+ ffffffff81bf6e60 ffff880807486168 000003ffffffffff 0000000003c87758
+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 XSA-174.
+
+Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
+Signed-off-by: Jan Beulich <jbeulich@suse.com>
+Cc: stable@vger.kernel.org
+---
+v2: Make Xen-inspecific, by using cpu_has_pse.
+---
+ 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 f8a29d2..e6a8613 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,
+-- 
+2.8.0.rc3
+

debian/patches/series

@@ -123,6 +123,7 @@ bugfix/all/netfilter-x_tables-validate-e-target_offset-early.patch
 bugfix/all/netfilter-x_tables-make-sure-e-next_offset-covers-re.patch
 bugfix/all/ipv4-don-t-do-expensive-useless-work-during-inetdev-.patch
 bugfix/x86/x86-mm-32-enable-full-randomization-on-i386-and-x86_.patch
+bugfix/x86/x86-xen-suppress-hugetlbfs-in-PV-guests.patch
 
 # Tools bug fixes
 bugfix/all/usbip-document-tcp-wrappers.patch