[PATCH 3.13.y-ckt 046/143] PCI: Fix infinite loop with ROM image of size 0

[Kamal Mostafa]

3.13.11-ckt18 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Michel=20D=C3=A4nzer?= <michel.daenzer at amd.com>

commit 16b036af31e1456cb69243a5a0c9ef801ecd1f17 upstream.

If the image size would ever read as 0, pci_get_rom_size() could keep
processing the same image over and over again.  Exit the loop if we ever
read a length of zero.

This fixes a soft lockup on boot when the radeon driver calls
pci_get_rom_size() on an AMD Radeon R7 250X PCIe discrete graphics card.

[bhelgaas: changelog, reference]
Link: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1386973
Reported-by: Federico <federicotg at gmail.com>
Signed-off-by: Michel Dänzer <michel.daenzer at amd.com>
Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/pci/rom.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/rom.c b/drivers/pci/rom.c
index c5d0a08..d6d4997 100644
--- a/drivers/pci/rom.c
+++ b/drivers/pci/rom.c
@@ -69,6 +69,7 @@ size_t pci_get_rom_size(struct pci_dev *pdev, void __iomem *rom, size_t size)
 {
 	void __iomem *image;
 	int last_image;
+	unsigned length;
 
 	image = rom;
 	do {
@@ -91,9 +92,9 @@ size_t pci_get_rom_size(struct pci_dev *pdev, void __iomem *rom, size_t size)
 		if (readb(pds + 3) != 'R')
 			break;
 		last_image = readb(pds + 21) & 0x80;
-		/* this length is reliable */
-		image += readw(pds + 16) * 512;
-	} while (!last_image);
+		length = readw(pds + 16);
+		image += length * 512;
+	} while (length && !last_image);
 
 	/* never return a size larger than the PCI resource window */
 	/* there are known ROMs that get the size wrong */
-- 
1.9.1