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[Xen-devel] [V1 PATCH] PVH: avoid call to handle_mmio

handle_mmio() is currently unsafe for pvh guests. A call to it would
result in call to vioapic_range that will crash xen since the vioapic
ptr in struct hvm_domain is not initialized for pvh guests.

However, one path exists for such a call. If a pvh guest, dom0 or domU,
unintentionally touches non-existing memory, an EPT violation would occur.
This would result in unconditional call to hvm_hap_nested_page_fault. In
that function, because get_gfn_type_access returns p2m_mmio_dm for non
existing mfns by default, handle_mmio() will get called. This would result
in xen crash instead of the guest crash. This patch addresses that.

Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
 xen/arch/x86/hvm/hvm.c | 5 +++++
 xen/arch/x86/hvm/io.c  | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index efbf6d9..51089b3 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -2079,6 +2079,11 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
          (access_w && (p2mt == p2m_ram_ro)) )
         put_gfn(p2m->domain, gfn);
+        rc = 0;
+        if ( unlikely(is_pvh_vcpu(v)) )
+            goto out;
         if ( !handle_mmio() )
             hvm_inject_hw_exception(TRAP_gp_fault, 0);
         rc = 1;
diff --git a/xen/arch/x86/hvm/io.c b/xen/arch/x86/hvm/io.c
index e6cb5e2..b53395e 100644
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -84,6 +84,8 @@ int handle_mmio(void)
     struct hvm_vcpu_io *vio = &curr->arch.hvm_vcpu.hvm_io;
     int rc;
+    ASSERT(!is_pvh_vcpu(current));
     hvm_emulate_prepare(&ctxt, guest_cpu_user_regs());
     rc = hvm_emulate_one(&ctxt);

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