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Date:   Thu, 12 Jul 2018 17:28:43 +0800
From:   Zhen Lei <>
To:     Jean-Philippe Brucker <>,
        Robin Murphy <>,
        Will Deacon <>,
        Joerg Roedel <>,
        linux-arm-kernel <>,
        iommu <>,
        linux-kernel <>
CC:     Zhen Lei <>
Subject: [PATCH 1/1] iommu/arm-smmu-v3: prevent any devices access to memory without registration

Stream bypass is not security. A malicious device can be hot plugged
without match any drivers, but it can access to any memory. So change to
disable bypass by default.

Signed-off-by: Zhen Lei <>
 drivers/iommu/arm-smmu-v3.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index 1d64710..b0ec28d 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -366,7 +366,7 @@
 #define MSI_IOVA_BASE			0x8000000
 #define MSI_IOVA_LENGTH			0x100000

-static bool disable_bypass;
+static bool disable_bypass = 1;
 module_param_named(disable_bypass, disable_bypass, bool, S_IRUGO);
 	"Disable bypass streams such that incoming transactions from devices that are not attached to an iommu domain will report an abort back to the device and will not be allowed to pass through the SMMU.");

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