  Recent years have brought microarchitectural security intothe spotlight,
proving that modern CPUs are vulnerable toseveral classes of microarchitectural
attacks. These attacksbypass the basic isolation primitives provided by the
CPUs:process isolation, memory permissions, access checks, andso on.
Nevertheless, most of the research was focused on In-tel CPUs, with only a few
exceptions. As a result, few vulner-abilities have been found in other CPUs,
leading to specula-tions about their immunity to certain types of
microarchi-tectural attacks. In this paper, we provide a black-box anal-ysis of
one of these under-explored areas. Namely, we inves-tigate the flaw of AMD CPUs
which may lead to a transientexecution hijacking attack. Contrary to nominal
immunity,we discover that AMD Zen family CPUs exhibit transient ex-ecution
patterns similar for Meltdown/MDS. Our analysisof exploitation possibilities
shows that AMDs design deci-sions indeed limit the exploitability scope
comparing to In-tel CPUs, yet it may be possible to use them to amplify
othermicroarchitectural attacks.
