From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S970113AbeEXMXw (ORCPT ); Thu, 24 May 2018 08:23:52 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:43394 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965995AbeEXMXr (ORCPT ); Thu, 24 May 2018 08:23:47 -0400 Date: Thu, 24 May 2018 13:24:14 +0100 From: Will Deacon To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu, Catalin Marinas , Thomas Gleixner , Andy Lutomirski , Kees Cook , Greg Kroah-Hartman , Christoffer Dall Subject: Re: [PATCH 10/14] arm64: ssbd: Add prctl interface for per-thread mitigation Message-ID: <20180524122413.GD8689@arm.com> References: <20180522150648.28297-1-marc.zyngier@arm.com> <20180522150648.28297-11-marc.zyngier@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180522150648.28297-11-marc.zyngier@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 22, 2018 at 04:06:44PM +0100, Marc Zyngier wrote: > 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. > > Signed-off-by: Marc Zyngier > --- > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/ssbd.c | 107 +++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 108 insertions(+) > create mode 100644 arch/arm64/kernel/ssbd.c > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index bf825f38d206..0025f8691046 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -54,6 +54,7 @@ arm64-obj-$(CONFIG_ARM64_RELOC_TEST) += arm64-reloc-test.o > arm64-reloc-test-y := reloc_test_core.o reloc_test_syms.o > arm64-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o > arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o > +arm64-obj-$(CONFIG_ARM64_SSBD) += ssbd.o > > obj-y += $(arm64-obj-y) vdso/ probes/ > obj-m += $(arm64-obj-m) > diff --git a/arch/arm64/kernel/ssbd.c b/arch/arm64/kernel/ssbd.c > new file mode 100644 > index 000000000000..34e3c430176b > --- /dev/null > +++ b/arch/arm64/kernel/ssbd.c > @@ -0,0 +1,107 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Copyright (C) 2018 ARM Ltd, All Rights Reserved. > + */ > + > +#include > +#include > + > +#include > + > +/* > + * prctl interface for SSBD > + * FIXME: Drop the below ifdefery once the common interface has been merged. > + */ > +#ifdef PR_SPEC_STORE_BYPASS > +static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl) > +{ > + int state = arm64_get_ssbd_state(); > + > + /* Unsupported or already mitigated */ > + if (state == ARM64_SSBD_UNKNOWN) > + return -EINVAL; > + if (state == ARM64_SSBD_MITIGATED) > + return -EPERM; I'm not sure this is the best thing to do. If the firmware says that the CPU is mitigated, we should probably return 0 for PR_SPEC_DISABLE but -EPERM for PR_SPEC_ENABLE (i.e. the part that doesn't work is disabling the mitigation). Will From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Thu, 24 May 2018 13:24:14 +0100 Subject: [PATCH 10/14] arm64: ssbd: Add prctl interface for per-thread mitigation In-Reply-To: <20180522150648.28297-11-marc.zyngier@arm.com> References: <20180522150648.28297-1-marc.zyngier@arm.com> <20180522150648.28297-11-marc.zyngier@arm.com> Message-ID: <20180524122413.GD8689@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, May 22, 2018 at 04:06:44PM +0100, Marc Zyngier wrote: > 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. > > Signed-off-by: Marc Zyngier > --- > arch/arm64/kernel/Makefile | 1 + > arch/arm64/kernel/ssbd.c | 107 +++++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 108 insertions(+) > create mode 100644 arch/arm64/kernel/ssbd.c > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index bf825f38d206..0025f8691046 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -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-obj-$(CONFIG_CRASH_DUMP) += crash_dump.o > arm64-obj-$(CONFIG_ARM_SDE_INTERFACE) += sdei.o > +arm64-obj-$(CONFIG_ARM64_SSBD) += ssbd.o > > obj-y += $(arm64-obj-y) vdso/ probes/ > obj-m += $(arm64-obj-m) > diff --git a/arch/arm64/kernel/ssbd.c b/arch/arm64/kernel/ssbd.c > new file mode 100644 > index 000000000000..34e3c430176b > --- /dev/null > +++ b/arch/arm64/kernel/ssbd.c > @@ -0,0 +1,107 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Copyright (C) 2018 ARM Ltd, All Rights Reserved. > + */ > + > +#include > +#include > + > +#include > + > +/* > + * prctl interface for SSBD > + * FIXME: Drop the below ifdefery once the common interface has been merged. > + */ > +#ifdef PR_SPEC_STORE_BYPASS > +static int ssbd_prctl_set(struct task_struct *task, unsigned long ctrl) > +{ > + int state = arm64_get_ssbd_state(); > + > + /* Unsupported or already mitigated */ > + if (state == ARM64_SSBD_UNKNOWN) > + return -EINVAL; > + if (state == ARM64_SSBD_MITIGATED) > + return -EPERM; I'm not sure this is the best thing to do. If the firmware says that the CPU is mitigated, we should probably return 0 for PR_SPEC_DISABLE but -EPERM for PR_SPEC_ENABLE (i.e. the part that doesn't work is disabling the mitigation). Will