linux-kernel - Re: [PATCH 0/5] mlx5 ConnectX diagnostic misc driver

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Message-ID: <2023101859-wanting-unmixed-7cfe@gregkh>
Date:   Wed, 18 Oct 2023 14:11:20 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Saeed Mahameed <saeed@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        linux-kernel@...r.kernel.org, Leon Romanovsky <leonro@...dia.com>,
        Jiri Pirko <jiri@...dia.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH 0/5] mlx5 ConnectX diagnostic misc driver

On Wed, Oct 18, 2023 at 09:00:25AM -0300, Jason Gunthorpe wrote:
> On Wed, Oct 18, 2023 at 10:31:23AM +0200, Greg Kroah-Hartman wrote:
> > On Wed, Oct 18, 2023 at 01:19:36AM -0700, Saeed Mahameed wrote:
> > > Historically a userspace program was used that accessed the PCI register
> > > and config space directly through /sys/bus/pci/.../XXX and could operate
> > > these debugging interfaces in parallel with the running driver.
> > > This approach is incompatible with secure boot and kernel lockdown so this
> > > driver provides a secure and restricted interface to that.
> > 
> > Why not just write a UIO driver for this hardware then?
> 
> The old mechanism relied on direct config space and sometimes mmio
> access to the PCI device. We did a security analysis and concluded
> that approach could not provide the required security for what our
> customers want from the secure boot and lockdown modes. We cannot
> allow a lockdown userspace direct access to those device registers.
> 
> So, it was redesigned to be RPC driven instead of having direct HW
> access. The RPCs allow the device to provide the required level of
> security.
> 
> This new misc driver does not expose any HW registers or interrupts to
> userspace, so it does not seem like a fit for UIO.

Ok, I'll not complain, I always like "real" drivers instead of UIO ones,
nice to see this happen!

thanks,

greg k-h