linux-kernel - Re: [PATCH 13/14] cxl/mem: Add limited Get Log command (0401h)

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Date:   Tue, 2 Feb 2021 15:57:03 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Ben Widawsky <ben.widawsky@...el.com>
Cc:     Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        linux-cxl@...r.kernel.org, Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Jon Masters <jcm@...masters.org>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Vishal Verma <vishal.l.verma@...el.com>,
        daniel.lll@...baba-inc.com,
        "John Groves (jgroves)" <jgroves@...ron.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>
Subject: Re: [PATCH 13/14] cxl/mem: Add limited Get Log command (0401h)

On Tue, Feb 2, 2021 at 3:51 PM Ben Widawsky <ben.widawsky@...el.com> wrote:
>
> On 21-02-01 13:28:48, Konrad Rzeszutek Wilk wrote:
> > On Fri, Jan 29, 2021 at 04:24:37PM -0800, Ben Widawsky wrote:
> > > The Get Log command returns the actual log entries that are advertised
> > > via the Get Supported Logs command (0400h). CXL device logs are selected
> > > by UUID which is part of the CXL spec. Because the driver tries to
> > > sanitize what is sent to hardware, there becomes a need to restrict the
> > > types of logs which can be accessed by userspace. For example, the
> > > vendor specific log might only be consumable by proprietary, or offline
> > > applications, and therefore a good candidate for userspace.
> > >
> > > The current driver infrastructure does allow basic validation for all
> > > commands, but doesn't inspect any of the payload data. Along with Get
> > > Log support comes new infrastructure to add a hook for payload
> > > validation. This infrastructure is used to filter out the CEL UUID,
> > > which the userspace driver doesn't have business knowing, and taints on
> > > invalid UUIDs being sent to hardware.
> >
> > Perhaps a better option is to reject invalid UUIDs?
> >
> > And if you really really want to use invalid UUIDs then:
> >
> > 1) Make that code wrapped in CONFIG_CXL_DEBUG_THIS_IS_GOING_TO..?
> >
> > 2) Wrap it with lockdown code so that you can't do this at all
> >    when in LOCKDOWN_INTEGRITY or such?
> >
>
> The commit message needs update btw as CEL is allowed in the latest rev of the
> patches.
>
> We could potentially combine this with the now added (in a branch) CONFIG_RAW
> config option. Indeed I think that makes sense. Dan, thoughts?

Yeah, unknown UUIDs blocking is the same risk as raw commands as a
vendor can trigger any behavior they want. A "CONFIG_RAW depends on
!CONFIG_INTEGRITY" policy sounds reasonable as well.