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Commit 9c06aab1 authored by Marc Zyngier's avatar Marc Zyngier Committed by Greg Kroah-Hartman
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arm64: ssbd: Add prctl interface for per-thread mitigation 



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: default avatarWill Deacon <will.deacon@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent cf14b896

arch/arm64/kernel/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -50,6 +50,7 @@ arm64-obj-$(CONFIG_RANDOMIZE_BASE) += kaslr.o 
arm64-obj-$(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

arch/arm64/kernel/ssbd.c

0 → 100644
+108 −0
Original line number Diff line number Diff line 
// 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;

	}

}