linux-kernel - Re: [PATCH v2 00/17] arm64 SSBD (aka Spectre-v4) mitigation

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Date:   Thu, 31 May 2018 17:55:27 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, Mark Rutland <mark.rutland@....com>,
        Kees Cook <keescook@...omium.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Will Deacon <will.deacon@....com>,
        Christoffer Dall <christoffer.dall@....com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Julien Grall <julien.grall@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 00/17] arm64 SSBD (aka Spectre-v4) mitigation

Hi Catalin,

On 31/05/18 17:41, Catalin Marinas wrote:
> On Tue, May 29, 2018 at 01:11:04PM +0100, Marc Zyngier wrote:
>> 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
>>     ARCH_FEATURES_FUNC_ID
> 
> I queued the 14 patches above for 4.18.

I just realized that your for-next/core branch is based on
4.17-rc4, which means arch/arm64/kernel/ssbd.c won't compile
(it relies on some of the symbols introduced with the x86
stuff in 4.17-rc7.

You can work around it by adding the following hack:

>From 8a0dbe9fb468c03b3913d17af9dce7358f899ee3 Mon Sep 17 00:00:00 2001
From: Marc Zyngier <marc.zyngier@....com>
Date: Thu, 31 May 2018 17:54:11 +0100
Subject: [PATCH] fixup! arm64: ssbd: Add prctl interface for per-thread
 mitigation

---
 arch/arm64/kernel/ssbd.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm64/kernel/ssbd.c b/arch/arm64/kernel/ssbd.c
index 07b12c034ec2..3432e5ef9f41 100644
--- a/arch/arm64/kernel/ssbd.c
+++ b/arch/arm64/kernel/ssbd.c
@@ -11,7 +11,9 @@
 
 /*
  * 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();
@@ -105,3 +107,4 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 		return -ENODEV;
 	}
 }
+#endif	/* PR_SPEC_STORE_BYPASS */
-- 
2.17.1


Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...