linux-kernel - [PATCH v2] iommu: fix amd_iommu=force

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <20181206213915.196205-1-yuzhao@google.com>
Date:   Thu,  6 Dec 2018 14:39:15 -0700
From:   Yu Zhao <yuzhao@...gle.com>
To:     Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH v2] iommu: fix amd_iommu=force_isolation

The parameter is still there but it's ignored. We need to check its
value before deciding to go into passthrough mode for AMD IOMMU v2
capable device.

We occasionally use this parameter to force v2 capable device into
translation mode to debug memory corruption that we suspect is
caused by DMA writes.

To address the following comment from Joerg Roedel on the first
version, v2 capability of device is completely ignored.
> This breaks the iommu_v2 use-case, as it needs a direct mapping for the
> devices that support it.

And from Documentation/admin-guide/kernel-parameters.txt:
  This option does not override iommu=pt

Fixes: aafd8ba0ca74 ("iommu/amd: Implement add_device and remove_device")

Signed-off-by: Yu Zhao <yuzhao@...gle.com>
---
 drivers/iommu/amd_iommu.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
index 1167ff0416cf..325f3bad118b 100644
--- a/drivers/iommu/amd_iommu.c
+++ b/drivers/iommu/amd_iommu.c
@@ -438,7 +438,14 @@ static int iommu_init_device(struct device *dev)
 
 	dev_data->alias = get_alias(dev);
 
-	if (dev_is_pci(dev) && pci_iommuv2_capable(to_pci_dev(dev))) {
+	/*
+	 * By default we use passthrough mode for IOMMUv2 capable device.
+	 * But if amd_iommu=force_isolation is set (e.g. to debug DMA to
+	 * invalid address), we ignore the capability for the device so
+	 * it'll be forced to go into translation mode.
+	 */
+	if ((iommu_pass_through || !amd_iommu_force_isolation) &&
+	    dev_is_pci(dev) && pci_iommuv2_capable(to_pci_dev(dev))) {
 		struct amd_iommu *iommu;
 
 		iommu = amd_iommu_rlookup_table[dev_data->devid];
-- 
2.20.0.rc2.403.gdbc3b29805-goog