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Subject[PATCH v2 00/17] arm64 SSBD (aka Spectre-v4) mitigation
Hi all,

This patch series implements the Linux kernel side of the "Spectre-v4"
(CVE-2018-3639) mitigation known as "Speculative Store Bypass Disable"

More information can be found at:

For all released Arm Cortex-A CPUs that are affected by this issue, then
the preferred mitigation is simply to set a chicken bit in the firmware
during CPU initialisation and therefore no change to Linux is required.
Other CPUs may require the chicken bit to be toggled dynamically (for
example, when switching between user-mode and kernel-mode) and this is
achieved by calling into EL3 via an SMC which has been published as part
of the latest SMCCC specification:

as well as an ATF update for the released ARM cores affected by SSBD:

These patches provide the following:

1. Safe probing of firmware to establish which CPUs in the system
require calling into EL3 as part of the mitigation.

2. For CPUs that require it, call into EL3 on exception entry/exit
from EL0 to apply the SSBD mitigation when running at EL1.

3. A command-line option to force the SSBD mitigation to be always on,
always off, or dymamically toggled (default) for CPUs that require
the EL3 call.

4. An initial implementation of a prctl() backend for arm64 that allows
userspace tasks to opt-in to the mitigation explicitly. This is
intended to match the interface provided by x86, and so we rely on
their core changes here. The seccomp interface is provided as an
extra set of patches, which I'd like *not* to see merged. The main
reason is that it is invasive, has ugly/unclear semantics, and could
probably be left to the existing prctl interface.

5. An initial implementation of the call via KVM, which exposes the
mitigation to the guest via an HVC interface. This isn't yet
complete and doesn't include save/restore functionality for the
workaround state.

All comments welcome,


* From v1 [1]:

- New TIF_SSBD_PENDING flag to enable the mitigation, atomically
converted to TIF_SSBD on exit to userspace. Moved the seccomp thing to
its own patch.
- Renamed do_ssbd() to arm64_set_ssbd_mitigation() early in the series
- Some spelling fixes
- Dropped the now unnecessary #ifdef in ssbd.c
- SSBD handling in entry.S default to NOP until patching comes in, which
itself got tiddied up
- Collected RBs


Marc Zyngier (17):
arm/arm64: smccc: Add SMCCC-specific return codes
arm64: Call ARCH_WORKAROUND_2 on transitions between EL0 and EL1
arm64: Add per-cpu infrastructure to call ARCH_WORKAROUND_2
arm64: Add ARCH_WORKAROUND_2 probing
arm64: Add 'ssbd' command-line option
arm64: ssbd: Add global mitigation state accessor
arm64: ssbd: Skip apply_ssbd if not using dynamic mitigation
arm64: ssbd: Restore mitigation status on CPU resume
arm64: ssbd: Introduce thread flag to control userspace mitigation
arm64: ssbd: Add prctl interface for per-thread mitigation
arm64: KVM: Add HYP per-cpu accessors
arm64: KVM: Add ARCH_WORKAROUND_2 support for guests
arm64: KVM: Handle guest's ARCH_WORKAROUND_2 requests
arm64: KVM: Add ARCH_WORKAROUND_2 discovery through
arm64: Add test_and_clear_flag and set_flag atomic assembler
arm64: ssbd: Enable delayed setting of TIF_SSBD
arm64: ssbd: Implement arch_seccomp_spec_mitigate

Documentation/admin-guide/kernel-parameters.txt | 17 +++
arch/arm/include/asm/kvm_host.h | 12 ++
arch/arm/include/asm/kvm_mmu.h | 5 +
arch/arm64/Kconfig | 9 ++
arch/arm64/include/asm/assembler.h | 37 +++++
arch/arm64/include/asm/cpucaps.h | 3 +-
arch/arm64/include/asm/cpufeature.h | 22 +++
arch/arm64/include/asm/kvm_asm.h | 30 +++-
arch/arm64/include/asm/kvm_host.h | 26 ++++
arch/arm64/include/asm/kvm_mmu.h | 24 ++++
arch/arm64/include/asm/thread_info.h | 2 +
arch/arm64/kernel/Makefile | 1 +
arch/arm64/kernel/asm-offsets.c | 1 +
arch/arm64/kernel/cpu_errata.c | 180 ++++++++++++++++++++++++
arch/arm64/kernel/entry.S | 46 ++++++
arch/arm64/kernel/hibernate.c | 11 ++
arch/arm64/kernel/ssbd.c | 115 +++++++++++++++
arch/arm64/kernel/suspend.c | 8 ++
arch/arm64/kvm/hyp/hyp-entry.S | 38 ++++-
arch/arm64/kvm/hyp/switch.c | 42 ++++++
arch/arm64/kvm/reset.c | 4 +
include/linux/arm-smccc.h | 10 ++
virt/kvm/arm/arm.c | 4 +
virt/kvm/arm/psci.c | 18 ++-
24 files changed, 659 insertions(+), 6 deletions(-)
create mode 100644 arch/arm64/kernel/ssbd.c


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