[PATCH 0/6] s390: improve speculative execution handling

Martin Schwidefsky
2018-01-17T09:48:33Z

This patch series implements multiple mitigations for the speculative
execution findings:
1. The definition of the gmb() barrier as currently used by the
distributions, we may have to find a better name for it
2. The architecture code for the nospec interfaces, the macros for
nospec_ptr and nospec_load just use the gmb() barrier
3. The enablement for firmware features to switch between different
branch prediction modes. It comes with a config option
CONFIG_KERNEL_NOBP, two new kernel parameters "nobp=[0|1]" and
"nospec", and a new system call s390_modify_bp.
With CONFIG_KERNEL_NOBP=y the new branch prediction mode is active
for the kernel code by default and can be switched off with "nospec"
or "nobp=0". With CONFIG_KERNEL_NOBP=n the new mode is inactive for
kernel code unless "nobp=1" is specified.
User space code can use the trapdoor system call s390_modify_bp to
set the new TIF_NOBP bit. This switches to the new branch prediction
mode for the lifetime of the task, any children of the task will
inherit this attribute.
The vCPU of a KVM guest will run with the new branch prediction
mode if either the associated qemu task has TIF_NOBP set or if the
KVM kernel code sets TIF_NOBP_GUEST. The later will require a small
update to KVM backend.
4. Transport channel reduction by clearing registers on interrupts,
system calls and KVM guest exits.

We are working on an equivalent for retpoline, stay tuned.

@Greg: I have started with the backports for the stable kernel releases,
but unless the interface for gmp/nospec_ptr/nospec_load is cast in stone
does it make sense to send them?

Christian Borntraeger (1):
KVM: s390: wire up seb feature

Martin Schwidefsky (5):
s390/alternative: use a copy of the facility bit mask
s390: implement nospec_[load|ptr]
s390: add options to change branch prediction behaviour for the kernel
s390: add system call to run tasks with modified branch prediction
s390: scrub registers on kernel entry and KVM exit

arch/s390/Kconfig | 17 +++++
arch/s390/include/asm/barrier.h | 38 ++++++++++
arch/s390/include/asm/facility.h | 18 +++++
arch/s390/include/asm/kvm_host.h | 3 +-
arch/s390/include/asm/lowcore.h | 3 +-
arch/s390/include/asm/processor.h | 1 +
arch/s390/include/asm/thread_info.h | 4 ++
arch/s390/include/uapi/asm/kvm.h | 4 +-
arch/s390/include/uapi/asm/unistd.h | 3 +-
arch/s390/kernel/alternative.c | 33 ++++++++-
arch/s390/kernel/early.c | 5 ++
arch/s390/kernel/entry.S | 134 +++++++++++++++++++++++++++++++++++-
arch/s390/kernel/ipl.c | 1 +
arch/s390/kernel/setup.c | 4 +-
arch/s390/kernel/smp.c | 6 +-
arch/s390/kernel/sys_s390.c | 8 +++
arch/s390/kernel/syscalls.S | 1 +
arch/s390/kvm/kvm-s390.c | 11 +++
arch/s390/kvm/vsie.c | 8 +++
include/uapi/linux/kvm.h | 1 +
20 files changed, 294 insertions(+), 9 deletions(-)

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2.7.4