[Xen-changelog] [xen master] IOMMU: default to always quarantining PCI devices

[patchbot@xxxxxxx]

commit ba2ab00bbb8c74e311a252d816d68dee47c779a0
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Nov 26 14:15:01 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Nov 26 14:15:01 2019 +0100

    IOMMU: default to always quarantining PCI devices
    
    XSA-302 relies on the use of libxl's "assignable-add" feature to prepare
    devices to be assigned to untrusted guests.
    
    Unfortunately, this is not considered a strictly required step for
    device assignment. The PCI passthrough documentation on the wiki
    describes alternate ways of preparing devices for assignment, and
    libvirt uses its own ways as well. Hosts where these alternate methods
    are used will still leave the system in a vulnerable state after the
    device comes back from a guest.
    
    Default to always quarantining PCI devices, but provide a command line
    option to revert back to prior behavior (such that people who both
    sufficiently trust their guests and want to be able to use devices in
    Dom0 again after they had been in use by a guest wouldn't need to
    "manually" move such devices back from DomIO to Dom0).
    
    This is XSA-306.
    
    Reported-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Wei Liu <wl@xxxxxxx>
---
 docs/misc/xen-command-line.pandoc | 8 +++++++-
 xen/drivers/passthrough/iommu.c   | 3 +++
 xen/drivers/passthrough/pci.c     | 3 ++-
 xen/include/xen/iommu.h           | 2 +-
 4 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index 0394d669c0..891d2d439f 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1219,7 +1219,7 @@ detection of systems known to misbehave upon accesses to 
that port.
 > Default: `new` unless directed-EOI is supported
 
 ### iommu
-    = List of [ <bool>, verbose, debug, force, required,
+    = List of [ <bool>, verbose, debug, force, required, quarantine,
                 sharept, intremap, intpost, crash-disable,
                 snoop, qinval, igfx, amd-iommu-perdev-intremap,
                 dom0-{passthrough,strict} ]
@@ -1257,6 +1257,12 @@ boolean (e.g. `iommu=no`) can override this and leave 
the IOMMUs disabled.
     will prevent Xen from booting if IOMMUs aren't discovered and enabled
     successfully.
 
+*   The `quarantine` boolean can be used to control Xen's behavior when
+    de-assigning devices from guests.  If enabled (the default), Xen always
+    quarantines such devices; they must be explicitly assigned back to Dom0
+    before they can be used there again.  If disabled, Xen will only
+    quarantine devices the toolstack hass arranged for getting quarantined.
+
 *   The `sharept` boolean controls whether the IOMMU pagetables are shared
     with the CPU-side HAP pagetables, or allocated separately.  Sharing
     reduces the memory overhead, but doesn't work in combination with CPU-side
diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index 8cbe908fff..656fdeb093 100644
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -30,6 +30,7 @@ bool_t __initdata iommu_enable = 1;
 bool_t __read_mostly iommu_enabled;
 bool_t __read_mostly force_iommu;
 bool_t __read_mostly iommu_verbose;
+bool __read_mostly iommu_quarantine = true;
 bool_t __read_mostly iommu_igfx = 1;
 bool_t __read_mostly iommu_snoop = 1;
 bool_t __read_mostly iommu_qinval = 1;
@@ -78,6 +79,8 @@ static int __init parse_iommu_param(const char *s)
         else if ( (val = parse_boolean("force", s, ss)) >= 0 ||
                   (val = parse_boolean("required", s, ss)) >= 0 )
             force_iommu = val;
+        else if ( (val = parse_boolean("quarantine", s, ss)) >= 0 )
+            iommu_quarantine = val;
         else if ( (val = parse_boolean("igfx", s, ss)) >= 0 )
             iommu_igfx = val;
         else if ( (val = parse_boolean("verbose", s, ss)) >= 0 )
diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 8e501a79a8..cbd232c131 100644
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -922,7 +922,8 @@ static int deassign_device(struct domain *d, uint16_t seg, 
uint8_t bus,
         return -ENODEV;
 
     /* De-assignment from dom_io should de-quarantine the device */
-    target = (pdev->quarantine && pdev->domain != dom_io) ?
+    target = ((pdev->quarantine || iommu_quarantine) &&
+              pdev->domain != dom_io) ?
         dom_io : hardware_domain;
 
     while ( pdev->phantom_stride )
diff --git a/xen/include/xen/iommu.h b/xen/include/xen/iommu.h
index 974bd3ffe8..fd45060e56 100644
--- a/xen/include/xen/iommu.h
+++ b/xen/include/xen/iommu.h
@@ -53,7 +53,7 @@ static inline bool_t dfn_eq(dfn_t x, dfn_t y)
 }
 
 extern bool_t iommu_enable, iommu_enabled;
-extern bool_t force_iommu, iommu_verbose, iommu_igfx;
+extern bool force_iommu, iommu_quarantine, iommu_verbose, iommu_igfx;
 extern bool_t iommu_snoop, iommu_qinval, iommu_intremap, iommu_intpost;
 
 #if defined(CONFIG_IOMMU_FORCE_PT_SHARE)
--
generated by git-patchbot for /home/xen/git/xen.git#master

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