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

[Chaitanya Kulkarni]

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

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

In case it is please ignore this.

-ck