Jan Beulich
2011-Mar-28 08:11 UTC
[Xen-devel] [PATCH] x86: guest_walk_tables() should check invalid bits on large page entries
The PSE handling doesn''t check bits 1...8 (or 1...9 for non-PAE guests)
being zero, thus allowing bad (not 2Mb/4Mb aligned) large pages to be
handled.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
--- a/xen/arch/x86/mm/guest_walk.c
+++ b/xen/arch/x86/mm/guest_walk.c
@@ -231,9 +231,28 @@ guest_walk_tables(struct vcpu *v, struct
/* _PAGE_PSE_PAT not set: remove _PAGE_PAT from flags. */
flags &= ~_PAGE_PAT;
+#define GUEST_L2_GFN_ALIGN (1 << (GUEST_L2_PAGETABLE_SHIFT - \
+ GUEST_L1_PAGETABLE_SHIFT))
+ if ( gfn_x(start) & (GUEST_L2_GFN_ALIGN - 1) & ~0x1 )
+ {
+#if GUEST_PAGING_LEVELS == 2
+ /*
+ * Note that _PAGE_INVALID_BITS is zero in this case, yielding a
+ * no-op here.
+ *
+ * Architecturally, the walk should fail if bit 21 is set (others
+ * aren''t being checked at least in PSE36 mode), but
we''ll ignore
+ * this here in order to avoid specifying a non-natural, non-zero
+ * _PAGE_INVALID_BITS value just for that case.
+ */
+#endif
+ rc |= _PAGE_INVALID_BITS;
+ }
+
/* Increment the pfn by the right number of 4k pages.
- * The ~0x1 is to mask out the PAT bit mentioned above. */
- start = _gfn((gfn_x(start) & ~0x1) + guest_l1_table_offset(va));
+ * Mask out PAT and invalid bits. */
+ start = _gfn((gfn_x(start) & ~(GUEST_L2_GFN_ALIGN - 1)) +
+ guest_l1_table_offset(va));
gw->l1e = guest_l1e_from_gfn(start, flags);
gw->l1mfn = _mfn(INVALID_MFN);
}
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Tim Deegan
2011-Apr-04 09:49 UTC
[Xen-devel] Re: [PATCH] x86: guest_walk_tables() should check invalid bits on large page entries
At 09:11 +0100 on 28 Mar (1301303519), Jan Beulich wrote:> The PSE handling doesn''t check bits 1...8 (or 1...9 for non-PAE guests) > being zero, thus allowing bad (not 2Mb/4Mb aligned) large pages to be > handled.Applied; thank you. Tim. -- Tim Deegan <Tim.Deegan@citrix.com> Principal Software Engineer, Xen Platform Team Citrix Systems UK Ltd. (Company #02937203, SL9 0BG) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel