linux-kernel - Re: [RFC PATCH v3 15/16] cxl/mem: Add limited Get Log command (0401h)

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Date:   Fri, 22 Jan 2021 16:14:10 -0800
From:   Ben Widawsky <ben.widawsky@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org,
        "linux-acpi@...r.kernel.org, Ira Weiny" <ira.weiny@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        "Kelley, Sean V" <sean.v.kelley@...el.com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Jon Masters <jcm@...masters.org>,
        Chris Browy <cbrowy@...ry-design.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        daniel.lll@...baba-inc.com
Subject: Re: [RFC PATCH v3 15/16] cxl/mem: Add limited Get Log command (0401h)

On 21-01-14 18:08:26, Jonathan Cameron wrote:
> On Mon, 11 Jan 2021 14:51:20 -0800
> Ben Widawsky <ben.widawsky@...el.com> 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.
> > 
> > Signed-off-by: Ben Widawsky <ben.widawsky@...el.com>
> 
> Just a minor question for this one.
> 
> Thanks, J
> ...                                              \
> > @@ -515,6 +529,15 @@ static int handle_mailbox_cmd_from_user(struct cxl_memdev *cxlmd,
> >  	int rc;
> >  
> >  	if (cmd->info.size_in) {
> > +		if (cmd->validate_payload) {
> > +			rc = cmd->validate_payload(u64_to_user_ptr(in_payload),
> > +						   cmd->info.size_in);
> 
> Is it worth moving this out of the region in which we hold the mbox?
> (after fixing the bug that I think means we don't actually hold it at this point)
> 
> Perhaps not, but it does feel odd to do validation under the lock.
> 
> 

When moving to a bounce buffer the locking resolves itself and ultimately this
doesn't happen under lock anymore.


        if (cmd->info.size_in) {
                if (cmd->validate_payload) {
                        rc = cmd->validate_payload(u64_to_user_ptr(in_payload),
                                                   cmd->info.size_in);
                        if (rc)
                                goto out;
                }

                mbox_cmd.payload_in = kvzalloc(cmd->info.size_in, GFP_KERNEL);
                if (!mbox_cmd.payload_in) {
                        rc = -ENOMEM;
                        goto out;
                }

                if (copy_from_user(mbox_cmd.payload_in,
                                   u64_to_user_ptr(in_payload),
                                   cmd->info.size_in)) {
                        rc = -EFAULT;
                        goto out;
                }
        }

	rc = cxl_mem_mbox_get(cxlm, true);

> > +			if (rc) {
> > +				cxl_mem_mbox_put(cxlmd->cxlm);
> > +				return -EFAULT;
> > +			}
> > +		}
> > +
> >  		/*
> >  		 * Directly copy the userspace payload into the hardware. UAPI
> >  		 * states that the buffer must already be little endian.