[Xen-devel] [PATCH] xen: Disable REP MOVSD optimization if introspection is active

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

REP MOVSD emulation is optimized to write several pages at once
if possible. While this is a very good thing in general, it
can interfere with a memory introspection application's ability
to detect suspect behaviour, since it supresses potentially
telling future page faults. This patch disables the optimization,
gated on introspection being active for the domain.

Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
---
 xen/arch/x86/hvm/emulate.c |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index c0f47d2..1848a33 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -885,6 +885,7 @@ static int hvmemul_rep_movs(
     p2m_type_t sp2mt, dp2mt;
     int rc, df = !!(ctxt->regs->eflags & X86_EFLAGS_DF);
     char *buf;
+    struct domain *currd = current->domain;
 
     rc = hvmemul_virtual_to_linear(
         src_seg, src_offset, bytes_per_rep, reps, hvm_access_read,
@@ -928,6 +929,10 @@ static int hvmemul_rep_movs(
         return hvmemul_do_mmio(
             dgpa, reps, bytes_per_rep, sgpa, IOREQ_WRITE, df, NULL);
 
+    /* Fall back to slow emulation if introspection is enabled. */
+    if ( currd->arch.hvm_domain.introspection_enabled )
+        return X86EMUL_UNHANDLEABLE;
+
     /* RAM-to-RAM copy: emulate as equivalent of memmove(dgpa, sgpa, bytes). */
     bytes = *reps * bytes_per_rep;
 
-- 
1.7.9.5


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