4.9-stable review patch. If anyone has any objections, please let me know.
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From: Marc Zyngier marc.zyngier@arm.com
commit 9cdc0108baa8ef87c76ed834619886a46bd70cbe upstream.
If running on a system that performs dynamic SSBD mitigation, allow userspace to request the mitigation for itself. This is implemented as a prctl call, allowing the mitigation to be enabled or disabled at will for this particular thread.
Acked-by: Will Deacon will.deacon@arm.com Signed-off-by: Marc Zyngier marc.zyngier@arm.com Signed-off-by: Catalin Marinas catalin.marinas@arm.com Signed-off-by: Marc Zyngier marc.zyngier@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/arm64/kernel/Makefile | 1 arch/arm64/kernel/ssbd.c | 108 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 109 insertions(+) create mode 100644 arch/arm64/kernel/ssbd.c
--- a/arch/arm64/kernel/Makefile +++ b/arch/arm64/kernel/Makefile @@ -50,6 +50,7 @@ arm64-obj-$(CONFIG_RANDOMIZE_BASE) += ka arm64-obj-$(CONFIG_HIBERNATION) += hibernate.o hibernate-asm.o arm64-obj-$(CONFIG_KEXEC) += machine_kexec.o relocate_kernel.o \ cpu-reset.o +arm64-obj-$(CONFIG_ARM64_SSBD) += ssbd.o
ifeq ($(CONFIG_KVM),y) arm64-obj-$(CONFIG_HARDEN_BRANCH_PREDICTOR) += bpi.o --- /dev/null +++ b/arch/arm64/kernel/ssbd.c @@ -0,0 +1,108 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright (C) 2018 ARM Ltd, All Rights Reserved. + */ + +#include <linux/errno.h> +#include <linux/prctl.h> +#include <linux/sched.h> +#include <linux/thread_info.h> + +#include <asm/cpufeature.h> + +/* + * prctl interface for SSBD + */ +static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl) +{ + int state = arm64_get_ssbd_state(); + + /* Unsupported */ + if (state == ARM64_SSBD_UNKNOWN) + return -EINVAL; + + /* Treat the unaffected/mitigated state separately */ + if (state == ARM64_SSBD_MITIGATED) { + switch (ctrl) { + case PR_SPEC_ENABLE: + return -EPERM; + case PR_SPEC_DISABLE: + case PR_SPEC_FORCE_DISABLE: + return 0; + } + } + + /* + * Things are a bit backward here: the arm64 internal API + * *enables the mitigation* when the userspace API *disables + * speculation*. So much fun. + */ + switch (ctrl) { + case PR_SPEC_ENABLE: + /* If speculation is force disabled, enable is not allowed */ + if (state == ARM64_SSBD_FORCE_ENABLE || + task_spec_ssb_force_disable(task)) + return -EPERM; + task_clear_spec_ssb_disable(task); + clear_tsk_thread_flag(task, TIF_SSBD); + break; + case PR_SPEC_DISABLE: + if (state == ARM64_SSBD_FORCE_DISABLE) + return -EPERM; + task_set_spec_ssb_disable(task); + set_tsk_thread_flag(task, TIF_SSBD); + break; + case PR_SPEC_FORCE_DISABLE: + if (state == ARM64_SSBD_FORCE_DISABLE) + return -EPERM; + task_set_spec_ssb_disable(task); + task_set_spec_ssb_force_disable(task); + set_tsk_thread_flag(task, TIF_SSBD); + break; + default: + return -ERANGE; + } + + return 0; +} + +int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which, + unsigned long ctrl) +{ + switch (which) { + case PR_SPEC_STORE_BYPASS: + return ssbd_prctl_set(task, ctrl); + default: + return -ENODEV; + } +} + +static int ssbd_prctl_get(struct task_struct *task) +{ + switch (arm64_get_ssbd_state()) { + case ARM64_SSBD_UNKNOWN: + return -EINVAL; + case ARM64_SSBD_FORCE_ENABLE: + return PR_SPEC_DISABLE; + case ARM64_SSBD_KERNEL: + if (task_spec_ssb_force_disable(task)) + return PR_SPEC_PRCTL | PR_SPEC_FORCE_DISABLE; + if (task_spec_ssb_disable(task)) + return PR_SPEC_PRCTL | PR_SPEC_DISABLE; + return PR_SPEC_PRCTL | PR_SPEC_ENABLE; + case ARM64_SSBD_FORCE_DISABLE: + return PR_SPEC_ENABLE; + default: + return PR_SPEC_NOT_AFFECTED; + } +} + +int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which) +{ + switch (which) { + case PR_SPEC_STORE_BYPASS: + return ssbd_prctl_get(task); + default: + return -ENODEV; + } +}