linux-kernel - Re: [PATCH RESEND] PCI/AER: Use a common function to print AER error bits

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Message-ID: <20180507220659.GB161390@bhelgaas-glaptop.roam.corp.google.com>
Date:   Mon, 7 May 2018 17:06:59 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Alex G." <mr.nuke.me@...il.com>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        gregkh@...uxfoundation.org, fred@...dlawl.com,
        linux-kernel@...r.kernel.org, alex_gagniuc@...lteam.com,
        austin_bolen@...l.com, keith.busch@...el.com
Subject: Re: [PATCH RESEND] PCI/AER: Use a common function to print AER error
 bits

On Mon, Apr 30, 2018 at 12:41:26PM -0500, Alex G. wrote:
> On 04/30/2018 12:15 PM, Bjorn Helgaas wrote:
> > On Sat, Apr 28, 2018 at 12:07:48PM -0500, Alex G. wrote:
> 
> (snip)
> >> I could update the offending line to say:
> >>  +	info.first_error = PCI_ERR_CAP_FEP(aer->cap_control);
> > 
> > That's what I would have expected.  So I'd say either do this, or add
> > a comment about why it's not the right thing to do.
> 
> Okay.
> 
> >> Though I still have the concerns with validating CPER data:
> >>
> >>> I can see a way to use even more common printk code, but that requires
> >>> validating the PCI regs we get from firmware. That means we need to make
> >>> a guarantee about CPER that is beyond the scope of this patch.
> > 
> > Sounds like this is material for another patch, but if/when you do
> > that, I'd like to understand your concern about validating the
> > registers we get from firmware.  Are you worried about getting
> > incorrect register contents, then printing the wrong info, making
> > the wrong decision about how to recover, something else?
> 
> I don't trust firmware, and I have daymares about firmware leaving these
> fields uninitialized. In jargon, I'd like to treat it as external
> untrusted serialized data.

That makes good sense to me.

In this particular case, we only test first_error for equality:

  __aer_print_error(...)
  {
    ...

      pci_err(dev, "   [%2d] %-22s%s\n", i, errmsg,
	info->first_error == i ? " (First)" : "");

so I don't think there's any danger.  If we were using it to index an
array or something, we should certainly validate it first.