From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ramana.Radhakrishnan@arm.com (Ramana Radhakrishnan)
Date: Tue, 23 Oct 2018 08:36:16 +0000
Subject: [PATCH v5 07/17] arm64: add basic pointer authentication support
In-Reply-To: <20181019111542.6wrvjguirglzg7vg@mbp>
References: <20181005084754.20950-1-kristina.martsenko@arm.com>
 <20181005084754.20950-8-kristina.martsenko@arm.com>
 <20181019111542.6wrvjguirglzg7vg@mbp>
Message-ID: <5ca5bf92-f2b7-48c9-ea41-5efeff09a799@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On 19/10/2018 12:15, Catalin Marinas wrote:
> On Fri, Oct 05, 2018 at 09:47:44AM +0100, Kristina Martsenko wrote:
>> diff --git a/arch/arm64/include/asm/pointer_auth.h b/arch/arm64/include/asm/pointer_auth.h
>> new file mode 100644
>> index 000000000000..2aefedc31d9e
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/pointer_auth.h
>> @@ -0,0 +1,63 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +#ifndef __ASM_POINTER_AUTH_H
>> +#define __ASM_POINTER_AUTH_H
>> +
>> +#include <linux/random.h>
>> +
>> +#include <asm/cpufeature.h>
>> +#include <asm/sysreg.h>
>> +
>> +#ifdef CONFIG_ARM64_PTR_AUTH
>> +/*
>> + * Each key is a 128-bit quantity which is split across a pair of 64-bit
>> + * registers (Lo and Hi).
>> + */
>> +struct ptrauth_key {
>> +	unsigned long lo, hi;
>> +};
>> +
>> +/*
>> + * We give each process its own instruction A key (APIAKey), which is shared by
>> + * all threads. This is inherited upon fork(), and reinitialised upon exec*().
>> + * All other keys are currently unused, with APIBKey, APDAKey, and APBAKey
>> + * instructions behaving as NOPs.
>> + */
> 
> I don't remember the past discussions but I assume the tools guys are ok
> with a single key shared by multiple threads. Ramana, could you ack this
> part, FTR?

Sorry about the slow response, I've been traveling.

Ack and Will's response covers the reasons why pretty well. A prctl call 
would be a good enhancement.

regards
Ramana