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From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: x86/hvm: Disallow the creation of HVM domains without Local APIC emulation
There are multiple problems, not necesserily limited to:
* Guests which configure event channels via hvmop_set_evtchn_upcall_vector(),
or which hit %cr8 emulation will cause Xen to fall over a NULL vlapic->regs
pointer.
* On Intel hardware, disabling the TPR_SHADOW execution control without
reenabling CR8_{LOAD,STORE} interception means that the guests %cr8
accesses interact with the real TPR. Amongst other things, setting the
real TPR to 0xf blocks even IPIs from interrupting this CPU.
* On hardware which sets up the use of Interrupt Posting, including
IOMMU-Posting, guests run without the appropriate non-root configuration,
which at a minimum will result in dropped interrupts.
Whether no-LAPIC mode is of any use at all remains to be seen.
This is XSA-256.
Reported-by: Ian Jackson <ian.jackson@eu.citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
index f93327b..f65fc12 100644
--- a/xen/arch/x86/domain.c
+++ b/xen/arch/x86/domain.c
@@ -413,7 +413,7 @@ static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
if ( is_hardware_domain(d) &&
emflags != (XEN_X86_EMU_LAPIC|XEN_X86_EMU_IOAPIC) )
return false;
- if ( !is_hardware_domain(d) && emflags &&
+ if ( !is_hardware_domain(d) &&
emflags != XEN_X86_EMU_ALL && emflags != XEN_X86_EMU_LAPIC )
return false;
}
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