linux-kernel - Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled

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Message-ID: <ddb58cbd-0a72-f680-80f4-ce09b13a2cee@suse.com>
Date:   Mon, 17 May 2021 16:13:55 +0200
From:   Jan Beulich <jbeulich@...e.com>
To:     Connor Davis <connojdavis@...il.com>
Cc:     Jann Horn <jannh@...gle.com>, Lee Jones <lee.jones@...aro.org>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2 1/4] usb: early: Avoid using DbC if already enabled

On 17.05.2021 15:48, Connor Davis wrote:
> 
> On 5/17/21 3:32 AM, Jan Beulich wrote:
>> On 14.05.2021 02:56, Connor Davis wrote:
>>> Check if the debug capability is enabled in early_xdbc_parse_parameter,
>>> and if it is, return with an error. This avoids collisions with whatever
>>> enabled the DbC prior to linux starting.
>> Doesn't this go too far and prevent use even if firmware (perhaps
>> mistakenly) left it enabled?
> 
> Yes, but how is one supposed to distinguish the broken firmware and 
> non-broken
> 
> firmware cases?

Well, a first step might be to only check if running virtualized.
And then if your running virtualized, there might be a way to
inquire the hypervisor?

Jan