  Spectre v1 attacks, which exploit conditional branch misprediction, are often
identified with attacks that bypass array bounds checking to leak data from a
victim's memory. Generally, however, Spectre v1 attacks can exploit any
conditional branch misprediction that makes the victim execute code
incorrectly. In this paper, we investigate speculative type confusion, a
Spectre v1 attack vector in which branch mispredictions make the victim execute
with variables holding values of the wrong type and thereby leak memory
content.
  We observe that speculative type confusion can be inadvertently introduced by
a compiler, making it extremely hard for programmers to reason about security
and manually apply Spectre mitigations. We thus set out to determine the extent
to which speculative type confusion affects the Linux kernel. Our analysis
finds exploitable and potentially-exploitable arbitrary memory disclosure
vulnerabilities. We also find many latent vulnerabilities, which could become
exploitable due to innocuous system changes, such as coding style changes.
  Our results suggest that Spectre mitigations which rely on
statically/manually identifying "bad" code patterns need to be rethought, and
more comprehensive mitigations are needed.
