File 5992f1e5-x86-grant-disallow-misaligned-PTEs.patch of Package xen.5854

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File 5992f1e5-x86-grant-disallow-misaligned-PTEs.patch of Package xen.5854

# Commit ce442926c2530da9376199dcc769436376ad2386
# Date 2017-08-15 15:06:45 +0200
# Author Andrew Cooper <andrew.cooper3@citrix.com>
# Committer Jan Beulich <jbeulich@suse.com>
x86/grant: disallow misaligned PTEs

Pagetable entries must be aligned to function correctly.  Disallow attempts
from the guest to have a grant PTE created at a misaligned address, which
would result in corruption of the L1 table with largely-guest-controlled
values.

This is CVE-2017-12137 / XSA-227.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -3783,6 +3783,9 @@ static int create_grant_pte_mapping(
     l1_pgentry_t ol1e;
     struct domain *d = v->domain;
 
+    if ( !IS_ALIGNED(pte_addr, sizeof(nl1e)) )
+        return GNTST_general_error;
+
     adjust_guest_l1e(nl1e, d);
 
     gmfn = pte_addr >> PAGE_SHIFT;
@@ -3840,6 +3843,16 @@ static int destroy_grant_pte_mapping(
     struct page_info *page;
     l1_pgentry_t ol1e;
 
+    /*
+     * addr comes from Xen's active_entry tracking so isn't guest controlled,
+     * but it had still better be PTE-aligned.
+     */
+    if ( !IS_ALIGNED(addr, sizeof(ol1e)) )
+    {
+        ASSERT_UNREACHABLE();
+        return GNTST_general_error;
+    }
+
     gmfn = addr >> PAGE_SHIFT;
     page = get_page_from_gfn(d, gmfn, NULL, P2M_ALLOC);
 
--- a/xen/include/xen/config.h
+++ b/xen/include/xen/config.h
@@ -83,6 +83,8 @@ int current_domain_id(void);
 
 #endif /* !__ASSEMBLY__ */
 
+#define IS_ALIGNED(val, align) (((val) & ((align) - 1)) == 0)
+
 #define __STR(...) #__VA_ARGS__
 #define STR(...) __STR(__VA_ARGS__)

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File 5992f1e5-x86-grant-disallow-misaligned-PTEs.patch of Package xen.5854

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