tree f721bd59b117ea8b002b218527ba32f04896606c
parent 1efbf4ecb8f3baa1d9b30b56934714a488d46f5c
author Will Deacon <will.deacon@arm.com> 1510676159 +0000
committer Todd Kjos <tkjos@google.com> 1515447451 -0800

arm64: use RET instruction for exiting the trampoline

Speculation attacks against the entry trampoline can potentially resteer
the speculative instruction stream through the indirect branch and into
arbitrary gadgets within the kernel.

This patch defends against these attacks by forcing a misprediction
through the return stack: a dummy BL instruction loads an entry into
the stack, so that the predicted program flow of the subsequent RET
instruction is to a branch-to-self instruction which is finally resolved
as a branch to the kernel vectors with speculation suppressed.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>