xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

thunderbolt: Export IOMMU based DMA protection support to userspace

Browse Source 
Recent systems with Thunderbolt ports may support IOMMU natively. In
practice this means that Thunderbolt connected devices are placed behind
an IOMMU during the whole time it is connected (including during boot)
making Thunderbolt security levels redundant. This is called Kernel DMA
protection [1] by Microsoft.

Some of these systems still have Thunderbolt security level set to
"user" in order to support OS downgrade (the older version of the OS
might not support IOMMU based DMA protection so connecting a device
still relies on user approval).

Export this information to userspace by introducing a new sysfs
attribute (iommu_dma_protection). Based on it userspace tools can make
more accurate decision whether or not authorize the connected device.

In addition update Thunderbolt documentation regarding IOMMU based DMA
protection.

[1] https://docs.microsoft.com/en-us/windows/security/information-protection/kernel-dma-protection-for-thunderbolt

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Yehezkel Bernat <YehezkelShB@gmail.com>
This commit is contained in:
Mika Westerberg
2018-10-31 14:06:52 +03:00
parent fb58fdcd29
commit dcc3c9e37f
3 changed files with 46 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
drivers/thunderbolt/domain.c
View File

@@ -7,7 +7,9 @@
*/
#include <linux/device.h>
#include <linux/dmar.h>
#include <linux/idr.h>
#include <linux/iommu.h>
#include <linux/module.h>
#include <linux/pm_runtime.h>
#include <linux/slab.h>
@@ -236,6 +238,20 @@ err_free_str:
}
static DEVICE_ATTR_RW(boot_acl);
static ssize_t iommu_dma_protection_show(struct device *dev,
struct device_attribute *attr,
char *buf)
{
/*
* Kernel DMA protection is a feature where Thunderbolt security is
* handled natively using IOMMU. It is enabled when IOMMU is
* enabled and ACPI DMAR table has DMAR_PLATFORM_OPT_IN set.
*/
return sprintf(buf, "%d\n",
iommu_present(&pci_bus_type) && dmar_platform_optin());
}
static DEVICE_ATTR_RO(iommu_dma_protection);
static ssize_t security_show(struct device *dev, struct device_attribute *attr,
char *buf)
{
@@ -251,6 +267,7 @@ static DEVICE_ATTR_RO(security);
static struct attribute *domain_attrs[] = {
&dev_attr_boot_acl.attr,
&dev_attr_iommu_dma_protection.attr,
&dev_attr_security.attr,
NULL,
};