linux-kernel - [PATCH v2] iommufd/iova_bitmap: Fix shift-out-of-bounds in iova_bitmap_offset_to

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Message-Id: <20250113223820.10713-1-qasdev00@gmail.com>
Date: Mon, 13 Jan 2025 22:38:20 +0000
From: Qasim Ijaz <qasdev00@...il.com>
To: jgg@...pe.ca,
	kevin.tian@...el.com,
	joro@...tes.org,
	will@...nel.org,
	robin.murphy@....com
Cc: iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	syzbot <syzbot+85992ace37d5b7b51635@...kaller.appspotmail.com>
Subject: [PATCH v2] iommufd/iova_bitmap: Fix shift-out-of-bounds in iova_bitmap_offset_to_index()

Resolve a UBSAN shift-out-of-bounds issue in iova_bitmap_offset_to_index() where
shifting the constant "1" (of type int) by bitmap->mapped.pgshift 
(an unsigned long value) could result in undefined behavior. 

The constant "1" defaults to a 32-bit "int", and when "pgshift" exceeds 31 (e.g., pgshift = 63)
the shift operation overflows, as the result cannot be represented in a 32-bit type.

To resolve this, the constant is updated to "1UL", promoting it to an unsigned long type 
to match the operand's type.

Reported-by: syzbot <syzbot+85992ace37d5b7b51635@...kaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=85992ace37d5b7b51635
Fixes: 58ccf0190d19 ("vfio: Add an IOVA bitmap support")
Signed-off-by: Qasim Ijaz <qasdev00@...il.com>
---
 drivers/iommu/iommufd/iova_bitmap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/iommufd/iova_bitmap.c b/drivers/iommu/iommufd/iova_bitmap.c
index ab665cf38ef4..39a86a4a1d3a 100644
--- a/drivers/iommu/iommufd/iova_bitmap.c
+++ b/drivers/iommu/iommufd/iova_bitmap.c
@@ -130,7 +130,7 @@ struct iova_bitmap {
 static unsigned long iova_bitmap_offset_to_index(struct iova_bitmap *bitmap,
 						 unsigned long iova)
 {
-	unsigned long pgsize = 1 << bitmap->mapped.pgshift;
+	unsigned long pgsize = 1UL << bitmap->mapped.pgshift;
 
 	return iova / (BITS_PER_TYPE(*bitmap->bitmap) * pgsize);
 }
-- 
2.39.5