Systems with microprocessors utilizing speculative execution and
speculative execution of memory reads before the addresses of all prior
memory writes are known may allow unauthorized disclosure of information to
an attacker with local user access via a side-channel analysis, aka
Speculative Store Bypass (SSB), Variant 4.

Jann Horn and Ken Johnson discovered that microprocessors utilizing
speculative execution of a memory read may allow unauthorized memory reads
via a sidechannel attack. This flaw is known as Spectre Variant 4. A local
attacker could use this to expose sensitive information, including kernel
memory.