Subject: [PATCH 13/20] alpha/PCI: Clean up __pci_mmap_fits()

From: Krzysztof Wilczyński <[email-masked]>
Date: Fri, 10 Apr 2026 05:50:33 +0000

Currently, __pci_mmap_fits() computes the BAR size using
pci_resource_len() - 1, which wraps to a large value when the
BAR length is zero, causing the bounds check to incorrectly
succeed.

Thus, add an early return for empty resources.

Also, remove the WARN() that fires when userspace attempts to
mmap beyond the BAR bounds.  The check still returns 0 to reject
the mapping, but the warning is excessive for normal operation.

A similar warning was removed from the PCI core in the commit
3b519e4ea618 ("PCI: fix size checks for mmap() on /proc/bus/pci files").

Signed-off-by: Krzysztof Wilczyński <[email-masked]>
---
 arch/alpha/kernel/pci-sysfs.c | 14 ++++++--------
 1 file changed, 6 insertions(+), 8 deletions(-)

diff --git a/arch/alpha/kernel/pci-sysfs.c b/arch/alpha/kernel/pci-sysfs.c
index 7aac5e76dcd6..867199b988de 100644
--- a/arch/alpha/kernel/pci-sysfs.c
+++ b/arch/alpha/kernel/pci-sysfs.c
@@ -37,20 +37,18 @@ static int hose_mmap_page_range(struct pci_controller *hose,
 static int __pci_mmap_fits(struct pci_dev *pdev, int num,
 			   struct vm_area_struct *vma, int sparse)
 {
+	resource_size_t len = pci_resource_len(pdev, num);
 	unsigned long nr, start, size;
 	int shift = sparse ? 5 : 0;
 
+	if (!len)
+		return 0;
+
 	nr = vma_pages(vma);
 	start = vma->vm_pgoff;
-	size = ((pci_resource_len(pdev, num) - 1) >> (PAGE_SHIFT - shift)) + 1;
+	size = ((len - 1) >> (PAGE_SHIFT - shift)) + 1;
 
-	if (start < size && size - start >= nr)
-		return 1;
-	WARN(1, "process \"%s\" tried to map%s 0x%08lx-0x%08lx on %s BAR %d "
-		"(size 0x%08lx)\n",
-		current->comm, sparse ? " sparse" : "", start, start + nr,
-		pci_name(pdev), num, size);
-	return 0;
+	return start < size && size - start >= nr;
 }
 
 /**
-- 
2.53.0