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

[Dan Williams]

On Tue, Feb 2, 2021 at 3:51 PM Ben Widawsky <ben.widawsky@xxxxxxxxx> 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.