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

[Will Deacon]

On Fri, Dec 19, 2025 at 03:28:58PM -0800, Chaitanya Kulkarni wrote:
> __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 at vger.kernel.org
> Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux at gmail.com>
> ---
>  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 at kernel.org>

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

Cheers,

Will