linux-kernel - Re: [PATCH v6 3/8] firmware_loader: Move module refcounts to allow unloading

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Message-ID: <6cffe226-928f-360f-20ae-bcf27a8d2c73@amd.com>
Date: Thu, 14 Nov 2024 13:30:16 -0600
From: Tom Lendacky <thomas.lendacky@....com>
To: Dan Williams <dan.j.williams@...el.com>,
 Russ Weight <russ.weight@...ux.dev>
Cc: Dionna Glaze <dionnaglaze@...gle.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, Luis Chamberlain <mcgrof@...nel.org>,
 Danilo Krummrich <dakr@...hat.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>,
 Tianfei zhang <tianfei.zhang@...el.com>, linux-coco@...ts.linux.dev,
 Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini
 <pbonzini@...hat.com>, Thomas Gleixner <tglx@...utronix.de>,
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
 Dave Hansen <dave.hansen@...ux.intel.com>,
 Ashish Kalra <ashish.kalra@....com>, John Allen <john.allen@....com>,
 Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>, Michael Roth
 <michael.roth@....com>, Alexey Kardashevskiy <aik@....com>,
 Russ Weight <russell.h.weight@...el.com>
Subject: Re: [PATCH v6 3/8] firmware_loader: Move module refcounts to allow
 unloading

On 11/14/24 12:17, Dan Williams wrote:
> Russ Weight wrote:
> [..]
>> Clearly this would be an unexpected/unusual case. Someone with root
>> access would have to remove the device driver. I'm not sure how much
>> effort should be expended in preventing it - but this is the reasoning
>> behind the incrementing/decrementing of the module reference counts.
> 
> The module reference needs to be held only if the producer of those
> symbols can be removed without triggering some coordinated removal with
> action consumer. A driver that fails to call
> firmware_upload_unregister() in its module removal path is simply a driver
> with a memory-leak and use-after-free bug, not something the firmware
> upload core needs to worry about.
> 
> So, the prevention mechanism is "thou shalt use
> firmware_upload_unregister() correctly", and when that is in place
> explicit module references are not only redundant, but trying to
> implement them causes circular dependency loops.

I believe that is how other similar services, like debugfs, work, the
module is responsible for cleaning up.

Thanks,
Tom