KVM: arm64: Don't inherit exec permission across page-table levels

KVM: arm64: Don't inherit exec permission across page-table levels

commit b757b47a2fcba584d4a32fd7ee68faca510ab96f upstream.

If a stage-2 page-table contains an executable, read-only mapping at the
pte level (e.g. due to dirty logging being enabled), a subsequent write
fault to the same page which tries to install a larger block mapping
(e.g. due to dirty logging having been disabled) will erroneously inherit
the exec permission and consequently skip I-cache invalidation for the
rest of the block.

Ensure that exec permission is only inherited by write faults when the
new mapping is of the same size as the existing one. A subsequent
instruction abort will result in I-cache invalidation for the entire
block mapping.

Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Tested-by: Quentin Perret <qperret@google.com>
Reviewed-by: Quentin Perret <qperret@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200723101714.15873-1-will@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>