From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lu Baolu Subject: [PATCH v2 07/10] iommu/vt-d: Check whether device requires bounce buffer Date: Wed, 27 Mar 2019 14:35:03 +0800 Message-ID: <20190327063506.32564-8-baolu.lu@linux.intel.com> References: <20190327063506.32564-1-baolu.lu@linux.intel.com> Return-path: In-Reply-To: <20190327063506.32564-1-baolu.lu@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: David Woodhouse , Joerg Roedel , ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com, kevin.tian@intel.com, mika.westerberg@linux.intel.com, pengfei.xu@intel.com Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, Lu Baolu , Jacob Pan List-Id: iommu@lists.linux-foundation.org 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 Cc: Jacob Pan Signed-off-by: Lu Baolu Tested-by: Xu Pengfei Tested-by: Mika Westerberg --- Documentation/admin-guide/kernel-parameters.txt | 5 +++++ drivers/iommu/intel-iommu.c | 17 +++++++++++++++++ 2 files changed, 22 insertions(+) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2b8ee90bb644..86880eb3fc73 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -1726,6 +1726,11 @@ Note that using this option lowers the security provided by tboot because it makes the system vulnerable to DMA attacks. + nobounce [Default off] + Do not use the bounce buffer for untrusted devices like + 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 3bfec944b0b8..b95a94f2fd5a 100644 --- a/drivers/iommu/intel-iommu.c +++ b/drivers/iommu/intel-iommu.c @@ -366,6 +366,7 @@ static int intel_iommu_strict; static int intel_iommu_superpage = 1; static int intel_iommu_sm; static int iommu_identity_mapping; +static int intel_no_bounce; #define IDENTMAP_ALL 1 #define IDENTMAP_GFX 2 @@ -382,6 +383,19 @@ EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped); static DEFINE_SPINLOCK(device_domain_lock); static LIST_HEAD(device_domain_list); +static inline bool device_needs_bounce(struct device *dev) +{ + struct pci_dev *pdev = NULL; + + if (intel_no_bounce) + return false; + + if (dev_is_pci(dev)) + pdev = to_pci_dev(dev); + + return pdev ? pdev->untrusted : false; +} + /* * Iterate over elements in device_domain_list and call the specified * callback @fn against each element. @@ -464,6 +478,9 @@ 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