Re: [PATCH] iommu/io-pgtable-arm: fix size_t signedness bug in unmap path

On 1/5/26 13:25, Will Deacon wrote:

On Fri, Dec 19, 2025 at 03:28:58PM -0800, Chaitanya Kulkarni wrote:

quoted

__arm_lpae_unmap() returns size_t but was returning -ENOENT (negative
error code) when encountering an unmapped PTE. Since size_t is unsigned,
-ENOENT (typically -2) becomes a huge positive value (0xFFFFFFFFFFFFFFFE
on 64-bit systems).

This corrupted value propagates through the call chain:
   __arm_lpae_unmap() returns -ENOENT as size_t
   -> arm_lpae_unmap_pages() returns it
   -> __iommu_unmap() adds it to iova address
   -> iommu_pgsize() triggers BUG_ON due to corrupted iova

This can cause IOVA address overflow in __iommu_unmap() loop and
trigger BUG_ON in iommu_pgsize() from invalid address alignment.

Fix by returning 0 instead of -ENOENT. The WARN_ON already signals
the error condition, and returning 0 (meaning "nothing unmapped")
is the correct semantic for size_t return type. This matches the
behavior of other io-pgtable implementations (io-pgtable-arm-v7s,
io-pgtable-dart) which return 0 on error conditions.

Fixes: 3318f7b5cefb ("iommu/io-pgtable-arm: Add quirk to quiet WARN_ON()")
Cc: stable@vger.kernel.org
Signed-off-by: Chaitanya Kulkarni <redacted>
---
  drivers/iommu/io-pgtable-arm.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c
index e6626004b323..05d63fe92e43 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c

@@ -637,7 +637,7 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data,
  	pte = READ_ONCE(*ptep);
  	if (!pte) {
  		WARN_ON(!(data->iop.cfg.quirks & IO_PGTABLE_QUIRK_NO_WARN));
-		return -ENOENT;
+		return 0;
  	}
  
  	/* If the size matches this level, we're in the right place */

Acked-by: Will Deacon <will@kernel.org>

Joerg -- please can you pick this one up for 6.19-rc?

Cheers,

Will

Joerg, gentle reminder on this if this is not already applied.

In case it is please ignore this.

-ck