linux-kernel - Re: [RFC PATCH 2/4] PCI: hv: Use vmbus_requestor to generate transaction IDs for VMbus hardening

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Message-ID: <20220401160036.GA437893@anparri>
Date:   Fri, 1 Apr 2022 18:00:36 +0200
From:   Andrea Parri <parri.andrea@...il.com>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Wei Hu <weh@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczynski <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 2/4] PCI: hv: Use vmbus_requestor to generate
 transaction IDs for VMbus hardening

> > @@ -91,6 +91,9 @@ static enum pci_protocol_version_t pci_protocol_versions[] = {
> >  /* space for 32bit serial number as string */
> >  #define SLOT_NAME_SIZE 11
> > 
> > +/* Size of requestor for VMbus */
> > +#define HV_PCI_RQSTOR_SIZE 64
> 
> Might include a comment about how this value was derived.  I *think*
> it is an arbitrary value based on the assumption that having more than
> one request outstanding is rare, and so 64 should be extremely generous
> in ensuring that we don't ever run out.

Right, I've added a comment to that effect.


> > @@ -2696,8 +2699,9 @@ static void hv_pci_onchannelcallback(void *context)
> >  	const int packet_size = 0x100;
> >  	int ret;
> >  	struct hv_pcibus_device *hbus = context;
> > +	struct vmbus_channel *chan = hbus->hdev->channel;
> 
> Having gotten the channel as a local variable, could also use the local as
> the first argument to vmbus_recvpacket_raw().

Applied.


> > @@ -2743,11 +2747,13 @@ static void hv_pci_onchannelcallback(void *context)
> >  		switch (desc->type) {
> >  		case VM_PKT_COMP:
> > 
> > -			/*
> > -			 * The host is trusted, and thus it's safe to interpret
> > -			 * this transaction ID as a pointer.
> > -			 */
> > -			comp_packet = (struct pci_packet *)req_id;
> > +			req_addr = chan->request_addr_callback(chan, req_id);
> > +			if (req_addr == VMBUS_RQST_ERROR) {
> > +				dev_warn_ratelimited(&hbus->hdev->device,
> > +						     "Invalid request ID\n");
> 
> Could you include the req_id value in the error message that is output?  I
> was recently debugging a problem in the storvsc driver where having that
> value would have been handy.

Sure.

Thanks,
  Andrea