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[Xen-devel] [PATCH 4/6] xsm: flask: change the interface and default policy for xsm_map_gmfn_foregin

The original xsm_map_gmfn_foregin policy checks if source domain has the proper
privileges over the target domain. Under this policy, it's not allowed if a Dom0
wants to map pages from one DomU to another, this restricts some useful yet not
dangerous usages of the API, such as sharing pages among DomU's by calling
XENMEM_add_to_physmap from Dom0.

Change the policy to: IIF current domain has the proper privilege on the
target domain and source domain, grant the access.

References to this xsm check have also been updated to pass the current
domain as a new parameter.

This is for the proposal "Allow setting up shared memory areas between VMs
from xl config file" (see [1]).

[1] https://lists.xenproject.org/archives/html/xen-devel/2017-07/msg03047.html

Signed-off-by: Zhongze Liu <blackskygg@xxxxxxxxx>

Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>
Cc: George Dunlap <george.dunlap@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Cc: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Cc: xen-devel@xxxxxxxxxxxxx
 xen/arch/arm/mm.c       | 2 +-
 xen/arch/x86/mm/p2m.c   | 2 +-
 xen/include/xsm/dummy.h | 6 ++++--
 xen/include/xsm/xsm.h   | 7 ++++---
 xen/xsm/flask/hooks.c   | 6 ++++--
 5 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index a810a056d7..9ec78d8c03 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -1284,7 +1284,7 @@ int xenmem_add_to_physmap_one(
             return -EINVAL;
-        rc = xsm_map_gmfn_foreign(XSM_TARGET, d, od);
+        rc = xsm_map_gmfn_foreign(XSM_TARGET, current->domain, d, od);
         if ( rc )
diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index e8a57d118c..a547fd00c0 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -2545,7 +2545,7 @@ int p2m_add_foreign(struct domain *tdom, unsigned long 
     if ( tdom == fdom )
         goto out;
-    rc = xsm_map_gmfn_foreign(XSM_TARGET, tdom, fdom);
+    rc = xsm_map_gmfn_foreign(XSM_TARGET, current->domain, tdom, fdom);
     if ( rc )
         goto out;
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 62fcea6f04..28dbc6f2a2 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -525,10 +525,12 @@ static XSM_INLINE int 
xsm_remove_from_physmap(XSM_DEFAULT_ARG struct domain *d1,
     return xsm_default_action(action, d1, d2);
-static XSM_INLINE int xsm_map_gmfn_foreign(XSM_DEFAULT_ARG struct domain *d, 
struct domain *t)
+static XSM_INLINE int xsm_map_gmfn_foreign(XSM_DEFAULT_ARG struct domain *cd,
+                                           struct domain *d, struct domain *t)
-    return xsm_default_action(action, d, t);
+    return xsm_default_action(action, cd, d) ||
+        xsm_default_action(action, cd, t);
 static XSM_INLINE int xsm_hvm_param(XSM_DEFAULT_ARG struct domain *d, unsigned 
long op)
diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
index 60c0fd6a62..a20654a803 100644
--- a/xen/include/xsm/xsm.h
+++ b/xen/include/xsm/xsm.h
@@ -85,7 +85,7 @@ struct xsm_operations {
     int (*memory_pin_page) (struct domain *d1, struct domain *d2, struct 
page_info *page);
     int (*add_to_physmap) (struct domain *d1, struct domain *d2);
     int (*remove_from_physmap) (struct domain *d1, struct domain *d2);
-    int (*map_gmfn_foreign) (struct domain *d, struct domain *t);
+    int (*map_gmfn_foreign) (struct domain *cd, struct domain *d, struct 
domain *t);
     int (*claim_pages) (struct domain *d);
     int (*console_io) (struct domain *d, int cmd);
@@ -372,9 +372,10 @@ static inline int xsm_remove_from_physmap(xsm_default_t 
def, struct domain *d1,
     return xsm_ops->remove_from_physmap(d1, d2);
-static inline int xsm_map_gmfn_foreign (xsm_default_t def, struct domain *d, 
struct domain *t)
+static inline int xsm_map_gmfn_foreign (xsm_default_t def, struct domain *cd,
+                                        struct domain *d, struct domain *t)
-    return xsm_ops->map_gmfn_foreign(d, t);
+    return xsm_ops->map_gmfn_foreign(cd, d, t);
 static inline int xsm_claim_pages(xsm_default_t def, struct domain *d)
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 91146275bb..3408b6b9e1 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1165,9 +1165,11 @@ static int flask_remove_from_physmap(struct domain *d1, 
struct domain *d2)
     return domain_has_perm(d1, d2, SECCLASS_MMU, MMU__PHYSMAP);
-static int flask_map_gmfn_foreign(struct domain *d, struct domain *t)
+static int flask_map_gmfn_foreign(struct domain *cd,
+                                  struct domain *d, struct domain *t)
-    return domain_has_perm(d, t, SECCLASS_MMU, MMU__MAP_READ | MMU__MAP_WRITE);
+    return domain_has_perm(cd, d, SECCLASS_MMU, MMU__MAP_READ | 
+        domain_has_perm(cd, t, SECCLASS_MMU, MMU__MAP_READ | MMU__MAP_WRITE);
 static int flask_hvm_param(struct domain *d, unsigned long op)

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