This adds a helper to check whether a device needs to
use bounce buffer. It also provides a boot time option
to disable the bounce buffer. Users can use this to
prevent the iommu driver from using the bounce buffer
for performance gain.
Cc: Ashok Raj <ashok....@intel.com>
Cc: Jacob Pan <jacob.jun....@linux.intel.com>
Cc: Kevin Tian <kevin.t...@intel.com>
Signed-off-by: Lu Baolu <baolu...@linux.intel.com>
Tested-by: Xu Pengfei <pengfei...@intel.com>
Tested-by: Mika Westerberg <mika.westerb...@intel.com>
---
Documentation/admin-guide/kernel-parameters.txt | 5 +++++
drivers/iommu/intel-iommu.c | 6 ++++++
2 files changed, 11 insertions(+)
diff --git a/Documentation/admin-guide/kernel-parameters.txt
b/Documentation/admin-guide/kernel-parameters.txt
index 4c1971960afa..f441a9cea5bb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1732,6 +1732,11 @@
Note that using this option lowers the security
provided by tboot because it makes the system
vulnerable to DMA attacks.
+ nobounce [Default off]
+ Disable bounce buffer for unstrusted devices such as
+ the Thunderbolt devices. This will treat the untrusted
+ devices as the trusted ones, hence might expose security
+ risks of DMA attacks.
intel_idle.max_cstate= [KNL,HW,ACPI,X86]
0 disables intel_idle and fall back on acpi_idle.
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index c4e0e4a9ee9e..fee5dff16e95 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -362,6 +362,7 @@ static int dmar_forcedac;
static int intel_iommu_strict;
static int intel_iommu_superpage = 1;
static int iommu_identity_mapping;
+static int intel_no_bounce;
#define IDENTMAP_ALL 1
#define IDENTMAP_GFX 2
@@ -375,6 +376,8 @@ EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped);
static DEFINE_SPINLOCK(device_domain_lock);
static LIST_HEAD(device_domain_list);
+#define device_needs_bounce(d) (!intel_no_bounce && dev_is_untrusted(d))
+
/*
* Iterate over elements in device_domain_list and call the specified
* callback @fn against each element.
@@ -457,6 +460,9 @@ static int __init intel_iommu_setup(char *str)
printk(KERN_INFO
"Intel-IOMMU: not forcing on after tboot. This
could expose security risk for tboot\n");
intel_iommu_tboot_noforce = 1;
+ } else if (!strncmp(str, "nobounce", 8)) {
+ pr_info("Intel-IOMMU: No bounce buffer. This could
expose security risks of DMA attacks\n");
+ intel_no_bounce = 1;
}
str += strcspn(str, ",");
--
2.17.1
