linux-kernel - Re: [PATCH v3 2/5] crypto: caam: Fix endless loop when RNG is already initialized

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Date:   Mon, 5 Feb 2018 08:45:59 +0000
From:   Horia Geantă <horia.geanta@....com>
To:     "Auer, Lukas" <lukas.auer@...ec.fraunhofer.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Aymen Sghaier <aymen.sghaier@....com>,
        "pure.logic@...us-software.ie" <pure.logic@...us-software.ie>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>
CC:     Peng Fan <peng.fan@....com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ryan.harkin@...aro.org" <ryan.harkin@...aro.org>,
        Fabio Estevam <fabio.estevam@....com>,
        "rui.silva@...aro.org" <rui.silva@...aro.org>,
        "herbert@...dor.apana.org.au" <herbert@...dor.apana.org.au>
Subject: Re: [PATCH v3 2/5] crypto: caam: Fix endless loop when RNG is already
 initialized

On 2/2/2018 2:54 PM, Auer, Lukas wrote:
> On Fri, 2018-02-02 at 11:20 +0000, Bryan O'Donoghue wrote:
>> On 01/02/18 12:16, Horia Geantă wrote:
>>> If the loop cannot exit based on value of "ret" != -EAGAIN, then it
>>> means
>>> caam_probe() will eventually fail due to ret == -EAGAIN:
>>> 	if (ret) {
>>> 		dev_err(dev, "failed to instantiate RNG");
>>> 		goto caam_remove;
>>> 	}
>>
>> For me it's an endless loop applying the first two
>>
>> https://patchwork.ozlabs.org/patch/866460/
>> https://patchwork.ozlabs.org/patch/866462/
>>
>> but not this one
>>
>> https://patchwork.ozlabs.org/patch/865890/
>>
[snip]
> 
> I think the problem lies in the instantiate_rng() function. If the
> driver is unable to acquire DEC0 it'll return -ENODEV. This should
> terminate the while loop in the probe function. However, the return
> value is never checked and is instead overwritten with -EAGAIN, causing
> the endless loop.
> 
> This problem only occurs if u-boot instantiates only one of the state
> handles (ent_delay doesn't get incremented) and the kernel runs in non-
> secure mode (DEC0 can't get acquired). Instantiating all state handles
> in u-boot therefore fixes this problem. In addition, the return value
> in instantiate_rng() should be handled correctly by including
> 
> if (ret)
> 	break;
> 
> right after "ret = run_descriptor_deco0(ctrldev, desc, &status);".
> 
Indeed, the error path is incorrect and should be fixed as you mentioned.
I will send a patch replacing this one.
Note that this fixes only the error path, meaning caam_probe() won't go into an
endless loop and instead will return -ENODEV, due to being unable to acquire
control of DECO0.

There are still a few hurdles to cross for CAAM to work in a TZ environment.

For e.g. could you please check / confirm whether DECO0MIDR (DECO0 MID registers
@0xA0, @0xA4) are set such that Linux kernel is allowed to r/w DECO0-related
registers?

Thanks,
Horia