From mboxrd@z Thu Jan  1 00:00:00 1970
From: mark.rutland@arm.com (Mark Rutland)
Date: Thu, 18 Feb 2016 11:34:07 +0000
Subject: KASAN issues with idle / hotplug area
In-Reply-To: <56C59101.80805@virtuozzo.com>
References: <20160212160652.GL31665@e104818-lin.cambridge.arm.com>
 <56C1E072.2090909@virtuozzo.com>
 <20160215185957.GB19413@e104818-lin.cambridge.arm.com>
 <56C31D1D.50708@virtuozzo.com> <20160217143950.GC32647@leverpostej>
 <20160217170110.GE32647@leverpostej>
 <20160217175656.GJ32647@leverpostej>
 <20160217191643.GK32647@leverpostej>
 <56C57F40.3050500@virtuozzo.com> <56C59101.80805@virtuozzo.com>
Message-ID: <20160218113407.GN32647@leverpostej>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Feb 18, 2016 at 12:38:09PM +0300, Andrey Ryabinin wrote:
> 
> 
> On 02/18/2016 11:22 AM, Andrey Ryabinin wrote:
> 
> > I see two options here:
> >  * completely disable instrumentation for drivers/firmware/psci.c
> >  * get back to assembly implementation
> 
> One more option is to allocate struct arm_smccc_res on stack of arm_smccc_[hvc, smc](), and return res.a0
> from arm_smccc_[hvc,smc]().

In general ARM SMCCC calls can return multiple values, and there are
callers that may care (even if they're not here just yet).

So we can't change the arm_smccc_{smc,hvc} prototypes, and adding
another asm function is somewhat self-defeating (an asm caller
of arm_smccc_* is more complex and slower than a direct SMC/HVC).

> So it will look like this:
> 
> asmlinkage unsigned long arm_smccc_hvc(unsigned long a0, unsigned long a1,
> 			unsigned long a2, unsigned long a3, unsigned long a4,
> 			unsigned long a5, unsigned long a6, unsigned long a7);
> 
> 
> static unsigned long __invoke_psci_fn_hvc(unsigned long function_id,
> 			unsigned long arg0, unsigned long arg1,
> 			unsigned long arg2)
> {
> 	return arm_smccc_hvc(function_id, arg0, arg1, arg2, 0, 0, 0, 0);
> }

While this looks like it might work today, it's going to be _extremely_
fragile -- other instrumentation might cause stack allocation and hence
shadow dirtying.

I'm not keen on this.

Thanks,
Mark.