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[Xen-devel] [PATCH 1/3] x86/HVM: __hvm_copy() should not write to p2m_ioreq_server pages

Commit 3bdec530a5 ("x86/HVM: split page straddling emulated accesses in
more cases") introduced a hvm_copy_to_guest_linear() attempt before
falling back to hvmemul_linear_mmio_write(). This is wrong for the
p2m_ioreq_server special case. That change widened a pre-existing issue
though: Other writes to such pages also need to be failed (or forced
through emulation), in particular hypercall buffer writes.

Reported-by: ??? <???@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3202,6 +3202,12 @@ static enum hvm_translation_result __hvm
         if ( res != HVMTRANS_okay )
             return res;
+        if ( (flags & HVMCOPY_to_guest) && p2mt == p2m_ioreq_server )
+        {
+            put_page(page);
+            return HVMTRANS_bad_gfn_to_mfn;
+        }
         p = (char *)__map_domain_page(page) + (addr & ~PAGE_MASK);
         if ( flags & HVMCOPY_to_guest )

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