linux-kernel - Re: [PATCH] PCI: fix a potential uninitentional integer overflow issue

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Date:   Thu, 5 Nov 2020 16:24:30 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Colin King <colin.king@...onical.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Christian König <christian.koenig@....com>,
        Stephen Bates <sbates@...thlin.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] PCI: fix a potential uninitentional integer overflow
 issue

On Wed, Oct 07, 2020 at 03:33:45PM +0300, Dan Carpenter wrote:
> On Wed, Oct 07, 2020 at 12:46:15PM +0100, Colin King wrote:
> > From: Colin Ian King <colin.king@...onical.com>
> > 
> > The shift of 1 by align_order is evaluated using 32 bit arithmetic
> > and the result is assigned to a resource_size_t type variable that
> > is a 64 bit unsigned integer on 64 bit platforms. Fix an overflow
> > before widening issue by using the BIT_ULL macro to perform the
> > shift.
> > 
> > Addresses-Coverity: ("Uninitentional integer overflow")

s/Uninitentional/Unintentional/
Also in subject (please also capitalize subject)

Doesn't Coverity also assign an ID number for this specific issue?
Can you include that as well, e.g.,

  Addresses-Coverity-ID: 1226899 ("Unintentional integer overflow")

> > Fixes: 07d8d7e57c28 ("PCI: Make specifying PCI devices in kernel parameters reusable")
> > Signed-off-by: Colin Ian King <colin.king@...onical.com>
> > ---
> >  drivers/pci/pci.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 6d4d5a2f923d..1a5844d7af35 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -6209,7 +6209,7 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
> >  			if (align_order == -1)
> >  				align = PAGE_SIZE;
> >  			else
> > -				align = 1 << align_order;
> > +				align = BIT_ULL(align_order);
> 
> "align_order" comes from sscanf() so Smatch thinks it's not trusted.
> Anything above 63 is undefined behavior.  There should be a bounds check
> on this but I don't know what the valid values of "align" are.

The spec doesn't explicitly say what the size limit for 64-bit BARs
is, but it does say 32-bit BARs can support up to 2GB (2^31).  So I
infer that 2^63 would be the limit for 64-bit BARs.

What about something like the following?  To me, BIT_ULL doesn't seem
like an advantage over "1ULL << ", but maybe there's a reason to use
it.

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 8b9bea8ba751..6e17d0a6828a 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -6197,19 +6197,21 @@ static resource_size_t pci_specified_resource_alignment(struct pci_dev *dev,
 	while (*p) {
 		count = 0;
 		if (sscanf(p, "%d%n", &align_order, &count) == 1 &&
-							p[count] == '@') {
+		    p[count] == '@') {
 			p += count + 1;
+			if (align_order > 63) {
+				pr_err("PCI: Invalid requested alignment (order %d)\n",
+				       align_order);
+				align_order = PAGE_SHIFT;
+			}
 		} else {
-			align_order = -1;
+			align_order = PAGE_SHIFT;
 		}
 
 		ret = pci_dev_str_match(dev, p, &p);
 		if (ret == 1) {
 			*resize = true;
-			if (align_order == -1)
-				align = PAGE_SIZE;
-			else
-				align = 1 << align_order;
+			align = 1ULL << align_order;
 			break;
 		} else if (ret < 0) {
 			pr_err("PCI: Can't parse resource_alignment parameter: %s\n",