linux-hardening - Re: [PATCH v3 04/18] soc: qcom: Add Qualcomm minidump kernel driver

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Date:   Thu, 4 May 2023 18:34:32 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Mukesh Ojha <quic_mojha@...cinc.com>, agross@...nel.org,
        andersson@...nel.org, konrad.dybcio@...aro.org, corbet@....net,
        keescook@...omium.org, tony.luck@...el.com, gpiccoli@...lia.com,
        catalin.marinas@....com, will@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, robh+dt@...nel.org,
        linus.walleij@...aro.org, linux-gpio@...r.kernel.org,
        srinivas.kandagatla@...aro.org
Cc:     linux-arm-msm@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 04/18] soc: qcom: Add Qualcomm minidump kernel driver

On 04/05/2023 17:21, Krzysztof Kozlowski wrote:
>>>
>>>> +	ret = qcom_minidump_init_apss_subsystem(md);
>>>> +	if (ret) {
>>>> +		dev_err(&pdev->dev, "apss minidump initialization failed: %d\n", ret);
>>>> +		goto unlock;
>>>> +	}
>>>> +
>>>> +	__md = md;
>>>
>>> No. This is a platform device, so it can have multiple instances.
>>
>> It can have only one instance that is created from SMEM driver probe.
> 
> Anyone can instantiate more of them.... how did you solve it?

To clarify - sprinkling more of singletons makes everything tightly
coupled, difficult to debug and non-portable. You cannot have two
instances, you have to control concurrent initialization by yourself in
each of such singletons.

I understand sometimes they are unavoidable, for example when this does
not map to hardware property. However here you have the parent - smem -
which can return you valid instance. Thus you avoid entire problem of
file-scope variables.

Best regards,
Krzysztof