tree df7f7110a9a72a08756a091f9ef8db755db87643
parent ce50e716c5895e01795691d5c10c3ac736456d30
author Anthony Steinhauser <asteinhauser@google.com> 1577114122 -0800
committer Jérôme Forissier <jerome@forissier.org> 1578342779 +0100

core: arm64: fix speculative execution past ERET vulnerability

Even though ERET always causes a jump to another address, aarch64 CPUs
speculatively execute following instructions as if the ERET
instruction was not a jump instruction.
The speculative execution does not cross privilege-levels (to the jump
target as one would expect), but it continues on the kernel privilege
level as if the ERET instruction did not change the control flow -
thus execution anything that is accidentally linked after the ERET
instruction. Later, the results of this speculative execution are
always architecturally discarded, however they can leak data using
microarchitectural side channels. This speculative execution is very
reliable (seems to be unconditional) and it manages to complete even
relatively performance-heavy operations (e.g. multiple dependent
fetches from uncached memory).

It was fixed by Linux [1], FreeBSD [2] and OpenBSD [3]. The misbehavior
is demonstrated in [4] and [5].

Link: [1] https://github.com/torvalds/linux/commit/679db70801da9fda91d26caf13bf5b5ccc74e8e8
Link: [2] https://github.com/freebsd/freebsd/commit/29fb48ace4186a41c409fde52bcf4216e9e50b61
Link: [3] https://github.com/openbsd/src/commit/3a08873ece1cb28ace89fd65e8f3c1375cc98de2
Link: [4] https://github.com/google/safeside/blob/master/demos/eret_hvc_smc_wrapper.cc
Link: [5] https://github.com/google/safeside/blob/master/kernel_modules/kmod_eret_hvc_smc/eret_hvc_smc_module.c

Signed-off-by: Anthony Steinhauser <asteinhauser@google.com>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>