target/i386: do not crash if microvm guest uses SGX CPUID leaves

sgx_epc_get_section assumes a PC platform is in use:

bool sgx_epc_get_section(int section_nr, uint64_t *addr, uint64_t *size)
{
    PCMachineState *pcms = PC_MACHINE(qdev_get_machine());

However, sgx_epc_get_section is called by CPUID regardless of whether
SGX state has been initialized or which platform is in use.  Check
whether the machine has the right QOM class and if not behave as if
there are no EPC sections.

Fixes: 1dec2e1f19f ("i386: Update SGX CPUID info according to hardware/KVM/user input", 2021-09-30)
Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2142
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
(cherry picked from commit 13be929aff804581b21e69087a9caf3698fd5c3c)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

diff --git a/hw/i386/sgx.c b/hw/i386/sgx.c
index 70305547d4acad28788d4cf5779a18feedd6251b..356f04b599b53791719a46ba1703d01c4b148d08 100644 (file)
--- a/hw/i386/sgx.c
+++ b/hw/i386/sgx.c
@@ -266,10 +266,12 @@ void hmp_info_sgx(Monitor *mon, const QDict *qdict)
 
 bool sgx_epc_get_section(int section_nr, uint64_t *addr, uint64_t *size)
 {
-    PCMachineState *pcms = PC_MACHINE(qdev_get_machine());
+    PCMachineState *pcms =
+        (PCMachineState *)object_dynamic_cast(qdev_get_machine(),
+                                              TYPE_PC_MACHINE);
     SGXEPCDevice *epc;
 
-    if (pcms->sgx_epc.size == 0 || pcms->sgx_epc.nr_sections <= section_nr) {
+    if (!pcms || pcms->sgx_epc.size == 0 || pcms->sgx_epc.nr_sections <= section_nr) {
         return true;
     }