linux-kernel - [PATCH v4 11/12] PCI/ASPM: Check if pcie_capability_read

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Date:   Fri, 31 Jul 2020 13:43:28 +0200
From:   "Saheed O. Bolarinwa" <refactormyself@...il.com>
To:     helgaas@...nel.org
Cc:     "Saheed O. Bolarinwa" <refactormyself@...il.com>,
        bjorn@...gaas.com, skhan@...uxfoundation.org,
        linux-pci@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH v4 11/12] PCI/ASPM: Check if pcie_capability_read_*() reads ~0

On failure pcie_capability_read_*() sets it's last parameter, val
to 0. However, with Patch 12/12, it is possible that val is set
to ~0 on failure. This would introduce a bug because
(x & x) == (~0 & x).

Since ~0 is an invalid value in here,

Add extra check for ~0 to the if condition to confirm failure.

Suggested-by: Bjorn Helgaas <bjorn@...gaas.com>
Signed-off-by: Saheed O. Bolarinwa <refactormyself@...il.com>
---
 drivers/pci/pcie/aspm.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pcie/aspm.c b/drivers/pci/pcie/aspm.c
index b17e5ffd31b1..5e84a5ee94b0 100644
--- a/drivers/pci/pcie/aspm.c
+++ b/drivers/pci/pcie/aspm.c
@@ -223,7 +223,7 @@ static bool pcie_retrain_link(struct pcie_link_state *link)
 	end_jiffies = jiffies + LINK_RETRAIN_TIMEOUT;
 	do {
 		pcie_capability_read_word(parent, PCI_EXP_LNKSTA, &reg16);
-		if (!(reg16 & PCI_EXP_LNKSTA_LT))
+		if ((reg16 == (u16)~0) || !(reg16 & PCI_EXP_LNKSTA_LT))
 			break;
 		msleep(1);
 	} while (time_before(jiffies, end_jiffies));
@@ -250,23 +250,23 @@ static void pcie_aspm_configure_common_clock(struct pcie_link_state *link)
 
 	/* Check downstream component if bit Slot Clock Configuration is 1 */
 	pcie_capability_read_word(child, PCI_EXP_LNKSTA, &reg16);
-	if (!(reg16 & PCI_EXP_LNKSTA_SLC))
+	if ((reg16 == (u16)~0) || !(reg16 & PCI_EXP_LNKSTA_SLC))
 		same_clock = 0;
 
 	/* Check upstream component if bit Slot Clock Configuration is 1 */
 	pcie_capability_read_word(parent, PCI_EXP_LNKSTA, &reg16);
-	if (!(reg16 & PCI_EXP_LNKSTA_SLC))
+	if ((reg16 == (u16)~0) || !(reg16 & PCI_EXP_LNKSTA_SLC))
 		same_clock = 0;
 
 	/* Port might be already in common clock mode */
 	pcie_capability_read_word(parent, PCI_EXP_LNKCTL, &reg16);
-	if (same_clock && (reg16 & PCI_EXP_LNKCTL_CCC)) {
+	if ((reg16 != (u16)~0) && same_clock && (reg16 & PCI_EXP_LNKCTL_CCC)) {
 		bool consistent = true;
 
 		list_for_each_entry(child, &linkbus->devices, bus_list) {
 			pcie_capability_read_word(child, PCI_EXP_LNKCTL,
 						  &reg16);
-			if (!(reg16 & PCI_EXP_LNKCTL_CCC)) {
+			if ((reg16 == (u16)~0) || !(reg16 & PCI_EXP_LNKCTL_CCC)) {
 				consistent = false;
 				break;
 			}
-- 
2.18.4