[PATCH 1/2] PCI: hv: Avoid a kmemleak false positive caused by the hbus buffer

[Tim Gardner]

From: Dexuan Cui <decui at microsoft.com>

BugLink: https://bugs.launchpad.net/bugs/1973758

With the recent 59bb47985c1d ("mm, sl[aou]b: guarantee natural
alignment for kmalloc(power-of-two)"), kzalloc() is able to allocate
a 4KB buffer that is guaranteed to be 4KB-aligned. Here the size and
alignment of hbus is important because hbus's field
retarget_msi_interrupt_params must not cross a 4KB page boundary.

Here we prefer kzalloc to get_zeroed_page(), because a buffer
allocated by the latter is not tracked and scanned by kmemleak, and
hence kmemleak reports the pointer contained in the hbus buffer
(i.e. the hpdev struct, which is created in new_pcichild_device() and
is tracked by hbus->children) as memory leak (false positive).

If the kernel doesn't have 59bb47985c1d, get_zeroed_page() *must* be
used to allocate the hbus buffer and we can avoid the kmemleak false
positive by using kmemleak_alloc() and kmemleak_free() to ask
kmemleak to track and scan the hbus buffer.

Reported-by: Lili Deng <v-lide at microsoft.com>
Signed-off-by: Dexuan Cui <decui at microsoft.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
Reviewed-by: Michael Kelley <mikelley at microsoft.com>
(backported from commit 877b911a5ba0733f62239055ee869f2e117b57da)
[rtg - context adjustment]
Signed-off-by: Tim Gardner <tim.gardner at canonical.com>
---
 drivers/pci/controller/pci-hyperv.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
index 6272e7dda1fe..ea5aded65ec1 100644
--- a/drivers/pci/controller/pci-hyperv.c
+++ b/drivers/pci/controller/pci-hyperv.c
@@ -3388,7 +3388,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 	 * hv_pcibus_device contains the hypercall arguments for retargeting in
 	 * hv_irq_unmask(). Those must not cross a page boundary.
 	 */
-	BUILD_BUG_ON(sizeof(*hbus) > PAGE_SIZE);
+	BUILD_BUG_ON(sizeof(*hbus) > HV_HYP_PAGE_SIZE);
 
 	bridge = devm_pci_alloc_host_bridge(&hdev->device, 0);
 	if (!bridge)
@@ -3412,7 +3412,7 @@ static int hv_pci_probe(struct hv_device *hdev,
 	 * positive by using kmemleak_alloc() and kmemleak_free() to ask
 	 * kmemleak to track and scan the hbus buffer.
 	 */
-	hbus = kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
+	hbus = (struct hv_pcibus_device *)kzalloc(HV_HYP_PAGE_SIZE, GFP_KERNEL);
 	if (!hbus)
 		return -ENOMEM;
 
@@ -3670,7 +3670,7 @@ static int hv_pci_remove(struct hv_device *hdev)
 
 	hv_put_dom_num(hbus->bridge->domain_nr);
 
-	free_page((unsigned long)hbus);
+	kfree(hbus);
 	return ret;
 }
 
-- 
2.36.1