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Date: Tue, 27 Feb 2024 18:24:38 +0100
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: Carlos =?iso-8859-1?Q?L=F3pez?= <clopez@suse.de>, cve@kernel.org,
	linux-kernel@vger.kernel.org, Bjorn Helgaas <bhelgaas@google.com>,
	Jonas Gorski <jonas.gorski@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Mika Westerberg <mika.westerberg@linux.intel.com>
Subject: Re: CVE-2023-52466: PCI: Avoid potential out-of-bounds read in
 pci_dev_for_each_resource()
Message-ID: <2024022706-kindle-tapering-5f66@gregkh>
References: <2024022709-magazine-handshake-50da@gregkh>
 <20240227150744.GA235367@bhelgaas>
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In-Reply-To: <20240227150744.GA235367@bhelgaas>

On Tue, Feb 27, 2024 at 09:07:44AM -0600, Bjorn Helgaas wrote:
> [+cc Mika, author of 09cc90063240]
> 
> On Tue, Feb 27, 2024 at 02:26:26PM +0100, Greg Kroah-Hartman wrote:
> > On Tue, Feb 27, 2024 at 02:18:51PM +0100, Carlos L?pez wrote:
> > > On 25/2/24 9:16, Greg Kroah-Hartman wrote:
> > > > There is no actual issue right now because we have another check
> > > > afterwards and the out-of-bounds read is not being performed. In
> > > > any case it's better code with this fixed, hence the proposed
> > > > change.
> > > 
> > > Given that there is no actual security issue this looks more like a
> > > hardening, and thus not deserving of a CVE, no?
> > 
> > This was a tricky one, I think it's needed as we do not know how people
> > are really using these macros, right?  If the PCI maintainer agrees (on
> > the cc:), I'll be glad to revoke it, it's their call.
> 
> 09cc90063240 ("PCI: Introduce pci_dev_for_each_resource()") added
> pci_dev_for_each_resource(), which expands to:
> 
>   for (...; res = (&(dev)->resource[(bar)]), bar < PCI_NUM_RESOURCES; ...)
> 
> We compute "res" before the bounds-check of "bar", so the pointer may
> be out-of-bounds, but the body of the pci_dev_for_each_resource() loop
> is never executed with that out-of-bounds value.
> 
> So I don't think this is a security issue, no matter how
> pci_dev_for_each_resource() is used, unless the mere presence of an
> invalid address in a register is an issue.

Ah, yeah, now I remember, stuff like this was fixed up in other loops as
just reading off into the wild can be a speculation issue and so we had
to fix up a bunch of places in the kernel where we did have "invalid
data" in a register.  The code didn't use that, but the processor would
fetch from there, and boom, speculation mess.  There's a whole research
paper published on this type of thing somewhere...

So let's keep this as a CVE unless someone really doesn't want it marked
as such.  Again, it is a "weakness that is fixed" in the kernel, and
because of that, a CVE can be allocated for it.

thanks,

greg k-h