Re: Coverity CIDs 138749, 138750: cnb20le_res() unintended sign extension

[Bjorn Helgaas <bhelgaas@google.com>]

On Thu, Apr 03, 2014 at 02:56:26PM -0600, Bjorn Helgaas wrote:
> Coverity complains about unintended sign extension in cnb20le_res() in
> arch/x86/pci/broadcom_bus.c here:
> 
> 60        word1 = read_pci_config_16(bus, slot, func, 0xc4);
>  61        word2 = read_pci_config_16(bus, slot, func, 0xc6);
>  62        if (word1 != word2) {
> 
> CID 138749 (#1 of 2): Unintended sign extension (SIGN_EXTENSION)
> sign_extension: Suspicious implicit sign extension: word1 with type
> unsigned short (16 bits, unsigned) is promoted in (word1 << 16) | 0 to
> type int (32 bits, signed), then sign-extended to type unsigned long
> long (64 bits, unsigned). If (word1 << 16) | 0 is greater than
> 0x7FFFFFFF, the upper bits of the result will all be 1.
>  63                res.start = (word1 << 16) | 0x0000;
>     CID 138750: Unintended sign extension (SIGN_EXTENSION) [select issue]

I propose the following patch for this.  Unless there's objection, I'll
queue this for v3.16.


x86/PCI: Fix Broadcom CNB20LE unintended sign extension

From: Bjorn Helgaas <bhelgaas@google.com>

In the expression "word1 << 16", word1 starts as u16, but is promoted to
a signed int, then sign-extended to resource_size_t, which is probably
not what was intended.  Cast to resource_size_t to avoid the sign
extension.

Found by Coverity (CID 138749, 138750).

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
---
 arch/x86/pci/broadcom_bus.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/pci/broadcom_bus.c b/arch/x86/pci/broadcom_bus.c
index 614392ced7d6..bb461cfd01ab 100644
--- a/arch/x86/pci/broadcom_bus.c
+++ b/arch/x86/pci/broadcom_bus.c
@@ -60,8 +60,8 @@ static void __init cnb20le_res(u8 bus, u8 slot, u8 func)
 	word1 = read_pci_config_16(bus, slot, func, 0xc4);
 	word2 = read_pci_config_16(bus, slot, func, 0xc6);
 	if (word1 != word2) {
-		res.start = (word1 << 16) | 0x0000;
-		res.end   = (word2 << 16) | 0xffff;
+		res.start = ((resource_size_t) word1 << 16) | 0x0000;
+		res.end   = ((resource_size_t) word2 << 16) | 0xffff;
 		res.flags = IORESOURCE_MEM | IORESOURCE_PREFETCH;
 		update_res(info, res.start, res.end, res.flags, 0);
 	}