Re: [PATCH] iommu/io-pgtable-arm: fix size_t signedness bug in unmap path
From: Rob Clark <hidden>
Date: 2025-12-20 14:35:33
Also in:
stable
On Fri, Dec 19, 2025 at 3:29 PM Chaitanya Kulkarni [off-list ref] 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@vger.kernel.org
Signed-off-by: Chaitanya Kulkarni <redacted>Reviewed-by: Rob Clark <robin.clark@oss.qualcomm.com>
quoted hunk ↗ jump to hunk
--- 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 */ --2.40.0