tree 4b4024071f8ee4bea58946e390514ef623b56321
parent ae52619cf7de3edb432c4b2f676c503146a42194
author Will Deacon <will.deacon@arm.com> 1510676159 +0000
committer Todd Kjos <tkjos@google.com> 1515447213 -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>