Re: [PATCH 1/2] dma-direct: Validate DMA mask against canonical DMA addresses
From: Suzuki K Poulose
Date: Tue Jan 20 2026 - 09:40:28 EST
On 20/01/2026 14:18, Aneesh Kumar K.V wrote:
Suzuki K Poulose <suzuki.poulose@xxxxxxx> writes:
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@xxxxxxxxxx>
---
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 ?
That is true only when the device is operating in untrusted mode?. For a
trusted device that mask is valid mask right?
Irrespective of the mode in which the device is operating, the DMA
address must include the fully qualified "{I}PA" address, right ?
i.e., "the Unencrypted" bit is only a software construct and the full
PA must be used, irrespective of the mode of the device.
Suzuki
-aneesh