linux-kernel - [PATCH v3] PCI: hv: Return zero, not garbage, when reading PCI_INTERRUPT

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Message-ID: <20240701202606.129606-1-wei.liu@kernel.org>
Date: Mon,  1 Jul 2024 20:26:05 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Linux on Hyper-V List <linux-hyperv@...r.kernel.org>
Cc: Wei Liu <wei.liu@...nel.org>,
	stable@...nel.org,
	Michael Kelley <mhklinux@...look.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Dexuan Cui <decui@...rosoft.com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Jake Oshins <jakeo@...rosoft.com>,
	linux-pci@...r.kernel.org (open list:PCI NATIVE HOST BRIDGE AND ENDPOINT DRIVERS),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v3] PCI: hv: Return zero, not garbage, when reading PCI_INTERRUPT_PIN

The intent of the code snippet is to always return 0 for both
PCI_INTERRUPT_LINE and PCI_INTERRUPT_PIN.

The check misses PCI_INTERRUPT_PIN. This patch fixes that.

This is discovered by this call in VFIO:

    pci_read_config_byte(vdev->pdev, PCI_INTERRUPT_PIN, &pin);

The old code does not set *val to 0 because it misses the check for
PCI_INTERRUPT_PIN. Garbage is returned in that case.

Fixes: 4daace0d8ce8 ("PCI: hv: Add paravirtual PCI front-end for Microsoft Hyper-V VMs")
Cc: stable@...nel.org
Signed-off-by: Wei Liu <wei.liu@...nel.org>
Reviewed-by: Michael Kelley <mhklinux@...look.com>
---
v3:
* Change commit subject line and message per Bjorn's suggestion
v2:
* Change the commit subject line and message
* Change the code according to feedback
---
 drivers/pci/controller/pci-hyperv.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 5992280e8110..cdd5be16021d 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -1130,8 +1130,8 @@ static void _hv_pcifront_read_config(struct hv_pci_dev *hpdev, int where,
 		   PCI_CAPABILITY_LIST) {
 		/* ROM BARs are unimplemented */
 		*val = 0;
-	} else if (where >= PCI_INTERRUPT_LINE && where + size <=
-		   PCI_INTERRUPT_PIN) {
+	} else if ((where >= PCI_INTERRUPT_LINE && where + size <= PCI_INTERRUPT_PIN) ||
+		   (where >= PCI_INTERRUPT_PIN && where + size <= PCI_MIN_GNT)) {
 		/*
 		 * Interrupt Line and Interrupt PIN are hard-wired to zero
 		 * because this front-end only supports message-signaled
-- 
2.43.0