[win-pv-devel] [PATCH] Make sure Mdl->StartVa is set by __AllocatePages()

[Paul Durrant <paul.durrant@xxxxxxxxxx>]

wdm.h carries this comment:

// Notice that while in the context of the subject thread, the base virtual
// address of a buffer mapped by an MDL may be referenced using the
// following:
//
//      Mdl->StartVa | Mdl->ByteOffset
//

Hence it is important that a mapped MDL has a valid StartVa field as well
as a valid MappedSystemVa field. Unfortunately, for reasons best known to
Microsoft, MmMapLockedPagesSpecifyCache() does not ensure this is the
case, so it needs to be fixed up by __AllocatePages() itself.

Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
---
 src/xenvkbd/util.h | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/src/xenvkbd/util.h b/src/xenvkbd/util.h
index 2d4d1c9..b82445e 100644
--- a/src/xenvkbd/util.h
+++ b/src/xenvkbd/util.h
@@ -219,7 +219,11 @@ __AllocatePages(
     if (MdlMappedSystemVa == NULL)
         goto fail3;
 
-    ASSERT3P(MdlMappedSystemVa, ==, Mdl->MappedSystemVa);
+    Mdl->StartVa = PAGE_ALIGN(MdlMappedSystemVa);
+
+    ASSERT3U(Mdl->ByteOffset, ==, 0);
+    ASSERT3P(Mdl->StartVa, ==, MdlMappedSystemVa);
+    ASSERT3P(Mdl->MappedSystemVa, ==, MdlMappedSystemVa);
 
     RtlZeroMemory(MdlMappedSystemVa, Mdl->ByteCount);
 
-- 
2.5.3


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