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

[Ben Widawsky]

On 21-02-02 15:57:03, Dan Williams wrote:
> 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.

What about LOCKDOWN_NONE though? I think we need something runtime for this.

Can we summarize the CONFIG options here?

CXL_MEM_INSECURE_DEBUG // no change
CXL_MEM_RAW_COMMANDS // if !security_locked_down(LOCKDOWN_NONE)

bool cxl_unsafe()
{
#ifndef CXL_MEM_RAW_COMMANDS
	return false;
#else
	return !security_locked_down(LOCKDOWN_NONE);
#endif
}

---

Did I get that right?