[Xen-devel] PATCH: Allow domains to share instruction pages with each other

[Michael Abd-El-Malek <mabdelm@xxxxxxxxxxx>]

Allow domains to share instruction pages with each other.

Xen changeset 4ec25db9326a (Nov 3, 2008) set the NX page bit on pages  
shared between domains.  That broke my ability to execute a binary  
whose pages are mapped from another domain.
My fix: I removed the NX page flag.  I don't see a security problem  
with this: if domain A maps a page from domain B, it somehow trusts  
it, and can do any additional checks after the page is mapped.  But  
absolutely disallowing execution of instructions from a mapped page  
seems a little too strict.
diff -r 7a87b3dffa69 -r 43693d552e09 xen/include/asm-x86/page.h
--- a/xen/include/asm-x86/page.h        Sun Dec 28 02:37:15 2008 -0500
+++ b/xen/include/asm-x86/page.h        Wed Jan 07 23:35:18 2009 -0500
@@ -317,7 +317,7 @@
   (_PAGE_PRESENT | _PAGE_RW | _PAGE_DIRTY | _PAGE_PCD |  
_PAGE_ACCESSED)
#define GRANT_PTE_FLAGS \
-    (_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_NX |  
_PAGE_GNTTAB)
+    (_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_DIRTY | _PAGE_GNTTAB)

#ifndef __ASSEMBLY__


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