arm64: ssbd: Add prctl interface for per-thread mitigation

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>
This commit is contained in:
Marc Zyngier 2018-05-29 13:11:14 +01:00 committed by Catalin Marinas
parent 9dd9614f54
commit 9cdc0108ba
2 changed files with 111 additions and 0 deletions

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@ -54,6 +54,7 @@ arm64-obj-$(CONFIG_ARM64_RELOC_TEST) += arm64-reloc-test.o
arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o
arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o
arm64-obj-$(CONFIG_ARM64_SSBD) += ssbd.o
obj-y += $(arm64-obj-y) vdso/ probes/ obj-y += $(arm64-obj-y) vdso/ probes/
obj-m += $(arm64-obj-m) obj-m += $(arm64-obj-m)

110
arch/arm64/kernel/ssbd.c Normal file
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@ -0,0 +1,110 @@
// SPDX-License-Identifier: GPL-2.0
/*
* Copyright (C) 2018 ARM Ltd, All Rights Reserved.
*/
#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/thread_info.h>
#include <asm/cpufeature.h>
/*
* prctl interface for SSBD
* FIXME: Drop the below ifdefery once merged in 4.18.
*/
#ifdef PR_SPEC_STORE_BYPASS
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;
}
}
#endif /* PR_SPEC_STORE_BYPASS */