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

Suzuki K Poulose
2026-01-20T09:59:11Z

On 20/01/2026 06:42, Aneesh Kumar K.V (Arm) wrote:
> 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);

This is wrong, isn't it ? For e.g., for CCA, even though the "Flag" is
added to the PA, it is really part of the actual "PA" and thus must be
checked against the full PA ?

Suzuki

> }
>
> static const struct bus_dma_region *dma_find_range(struct device *dev,