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

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Date:   Thu, 4 Feb 2021 10:55:40 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Dan Williams <dan.j.williams@...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 21-02-03 12:31:00, Dan Williams wrote:
> On Wed, Feb 3, 2021 at 10:16 AM Konrad Rzeszutek Wilk
> <konrad.wilk@...cle.com> wrote:
> >
> > On Wed, Feb 03, 2021 at 09:16:10AM -0800, Ben Widawsky wrote:
> > > On 21-02-02 15:57:03, Dan Williams wrote:
> > > > 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.
> > >
> > > 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()
> >
> > Would it be better if this inverted? Aka cxl_safe()..
> > ?
> > > {
> > > #ifndef CXL_MEM_RAW_COMMANDS
> 
> nit use IS_ENABLED() if this function lives in a C file, or provide
> whole alternate static inline versions in a header gated by ifdefs.
> 

I had done this independently since... but agreed.

> > >       return false;
> > > #else
> > >       return !security_locked_down(LOCKDOWN_NONE);
> >
> > :thumbsup:
> >
> > (Naturally this would inverted if this was cxl_safe()).
> >
> >
> > > #endif
> > > }
> > >
> > > ---
> > >
> > > Did I get that right?
> >
> > :nods:
> 
> Looks good which means it's time to bikeshed the naming. I'd call it
> cxl_raw_allowed(). As "safety" isn't the only reason for blocking raw,
> it's also to corral the userspace api. I.e. things like enforcing
> security passphrase material through the Linux keys api.

It actually got pushed into cxl_mem_raw_command_allowed()

static bool cxl_mem_raw_command_allowed(u16 opcode)
{
        int i;

        if (!IS_ENABLED(CONFIG_CXL_MEM_RAW_COMMANDS))
                return false;

        if (security_locked_down(LOCKDOWN_NONE))
                return false;

        if (raw_allow_all)
                return true;

        if (is_security_command(opcode))
                return false;

        for (i = 0; i < ARRAY_SIZE(disabled_raw_commands); i++)
                if (disabled_raw_commands[i] == opcode)
                        return false;

        return true;
}

That work for you?