[PATCH 1/2] dma-direct: Validate DMA mask against canonical DMA addresses

Aneesh Kumar K.V (Arm)
2026-01-20T06:43:23Z

On systems that apply an address encryption tag or mask to DMA addresses,
DMA mask validation must be performed against the canonical DMA address.
Using a non-canonical (e.g. encrypted or unencrypted) DMA address
can incorrectly fail capability checks, since architecture-specific
encryption bits are not part of the device’s actual DMA addressing
capability. For example, arm64 adds PROT_NS_SHARED to unencrypted DMA
addresses.

Fix this by validating device DMA masks against __phys_to_dma(), ensuring
that the architecture encryption mask does not influence the check.

Fixes: b66e2ee7b6c8 ("dma: Introduce generic dma_addr_*crypted helpers")
Signed-off-by: Aneesh Kumar K.V (Arm) <aneesh.kumar@kernel.org>
---
kernel/dma/direct.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
index 8e04f72baaa3..a5639e9415f5 100644
--- a/kernel/dma/direct.c
+++ b/kernel/dma/direct.c
@@ -580,12 +580,12 @@ int dma_direct_supported(struct device *dev, u64 mask)

/*
* This check needs to be against the actual bit mask value, so use
- * phys_to_dma_unencrypted() here so that the SME encryption mask isn't
+ * __phys_to_dma() here so that the arch specific encryption mask isn't
* part of the check.
*/
if (IS_ENABLED(CONFIG_ZONE_DMA))
min_mask = min_t(u64, min_mask, zone_dma_limit);
- return mask >= phys_to_dma_unencrypted(dev, min_mask);
+ return mask >= __phys_to_dma(dev, min_mask);
}

static const struct bus_dma_region *dma_find_range(struct device *dev,
--
2.43.0