[Pkg-xen-changes] [xen] 04/11: x86: guard against undue super page PTE creation
Bastian Blank
waldi at moszumanska.debian.org
Sun Nov 1 20:39:28 UTC 2015
This is an automated email from the git hooks/post-receive script.
waldi pushed a commit to branch develop
in repository xen.
commit c270ef05942a8ce35d78064aaa82f4f8360aff27
Author: Jan Beulich <jbeulich at suse.com>
Date: Thu Oct 29 13:48:09 2015 +0100
x86: guard against undue super page PTE creation
When optional super page support got added (commit bd1cd81d64 "x86: PV
support for hugepages"), two adjustments were missed: mod_l2_entry()
needs to consider the PSE and RW bits when deciding whether to use the
fast path, and the PSE bit must not be removed from L2_DISALLOW_MASK
unconditionally.
This is CVE-2015-7835 / XSA-148.
Reported-by: "栾尚聪(好风)" <shangcong.lsc at alibaba-inc.com>
Signed-off-by: Jan Beulich <jbeulich at suse.com>
Reviewed-by: Tim Deegan <tim at xen.org>
master commit: fe360c90ea13f309ef78810f1a2b92f2ae3b30b8
master date: 2015-10-29 13:35:07 +0100
(cherry picked from commit 2d094bd87072e26ac29b07917d31fcbf13892288)
Patch-Name: CVE-2015-7835.diff
---
xen/arch/x86/mm.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index 202ff76..fc65982 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -160,7 +160,10 @@ static void put_superpage(unsigned long mfn);
static uint32_t base_disallow_mask;
/* Global bit is allowed to be set on L1 PTEs. Intended for user mappings. */
#define L1_DISALLOW_MASK ((base_disallow_mask | _PAGE_GNTTAB) & ~_PAGE_GLOBAL)
-#define L2_DISALLOW_MASK (base_disallow_mask & ~_PAGE_PSE)
+
+#define L2_DISALLOW_MASK (unlikely(opt_allow_superpage) \
+ ? base_disallow_mask & ~_PAGE_PSE \
+ : base_disallow_mask)
#define l3_disallow_mask(d) (!is_pv_32bit_domain(d) ? \
base_disallow_mask : 0xFFFFF198U)
@@ -1839,7 +1842,10 @@ static int mod_l2_entry(l2_pgentry_t *pl2e,
}
/* Fast path for identical mapping and presence. */
- if ( !l2e_has_changed(ol2e, nl2e, _PAGE_PRESENT) )
+ if ( !l2e_has_changed(ol2e, nl2e,
+ unlikely(opt_allow_superpage)
+ ? _PAGE_PSE | _PAGE_RW | _PAGE_PRESENT
+ : _PAGE_PRESENT) )
{
adjust_guest_l2e(nl2e, d);
if ( UPDATE_ENTRY(l2, pl2e, ol2e, nl2e, pfn, vcpu, preserve_ad) )
--
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