[Xen-devel] [PATCH 2/2] hvm: convert access check for nested HVM to XSM

[Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>]

This adds an XSM hook for enabling nested HVM support, replacing an
IS_PRIV check.  This hook is a partial duplicate with the xsm_hvm_param
hook, but using the existing hook would require adding the index to the
hook and would require the use of a custom hook for the xsm-disabled
case (using XSM_OTHER, which is less immediately readable) - whereas
adding a new hook retains the clarity of the existing code.

Defining this new permission allows a security policy writer to allow
only certain guest types to use nested HVM features, or to disable it
completely.

Signed-off-by: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
Cc: Ian Campbell <ian.campbell@xxxxxxxxxx>
Cc: Jan Beulich <JBeulich@xxxxxxxx>
Cc: Keir Fraser <keir@xxxxxxx>
---
 tools/flask/policy/policy/modules/xen/xen.if | 3 ++-
 xen/arch/x86/hvm/hvm.c                       | 6 ++----
 xen/include/xsm/dummy.h                      | 6 ++++++
 xen/include/xsm/xsm.h                        | 6 ++++++
 xen/xsm/dummy.c                              | 1 +
 xen/xsm/flask/hooks.c                        | 6 ++++++
 xen/xsm/flask/policy/access_vectors          | 2 ++
 7 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/tools/flask/policy/policy/modules/xen/xen.if 
b/tools/flask/policy/policy/modules/xen/xen.if
index fbb329d..f6f24a5 100644
--- a/tools/flask/policy/policy/modules/xen/xen.if
+++ b/tools/flask/policy/policy/modules/xen/xen.if
@@ -54,7 +54,8 @@ define(`create_domain_common', `
        allow $1 $2:shadow enable;
        allow $1 $2:mmu { map_read map_write adjust memorymap physmap pinpage 
mmuext_op };
        allow $1 $2:grant setup;
-       allow $1 $2:hvm { cacheattr getparam hvmctl irqlevel pciroute sethvmc 
setparam pcilevel trackdirtyvram };
+       allow $1 $2:hvm { cacheattr getparam hvmctl irqlevel pciroute sethvmc
+                       setparam pcilevel trackdirtyvram nested };
 ')
 
 # create_domain(priv, target)
diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ea7adf6..49b656e 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -3911,11 +3911,9 @@ long do_hvm_op(unsigned long op, 
XEN_GUEST_HANDLE_PARAM(void) arg)
                     rc = -EINVAL;
                 break;
             case HVM_PARAM_NESTEDHVM:
-                if ( !IS_PRIV(current->domain) )
-                {
-                    rc = -EPERM;
+                rc = xsm_hvm_param_nested(XSM_PRIV, d);
+                if ( rc )
                     break;
-                }
                 if ( a.value > 1 )
                     rc = -EINVAL;
                 /* Remove the check below once we have
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 7986cda..4d63cf1 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -491,6 +491,12 @@ static XSM_INLINE int xsm_hvm_param(XSM_DEFAULT_ARG struct 
domain *d, unsigned l
     return xsm_default_action(action, current->domain, d);
 }
 
+static XSM_INLINE int xsm_hvm_param_nested(XSM_DEFAULT_ARG struct domain *d)
+{
+    XSM_ASSERT_ACTION(XSM_PRIV);
+    return xsm_default_action(action, current->domain, d);
+}
+
 #ifdef CONFIG_X86
 static XSM_INLINE int xsm_shadow_control(XSM_DEFAULT_ARG struct domain *d, 
uint32_t op)
 {
diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
index d8ee0c8..9d3f214 100644
--- a/xen/include/xsm/xsm.h
+++ b/xen/include/xsm/xsm.h
@@ -133,6 +133,7 @@ struct xsm_operations {
     long (*do_xsm_op) (XEN_GUEST_HANDLE_PARAM(xsm_op_t) op);
 
     int (*hvm_param) (struct domain *d, unsigned long op);
+    int (*hvm_param_nested) (struct domain *d);
 
 #ifdef CONFIG_X86
     int (*shadow_control) (struct domain *d, uint32_t op);
@@ -511,6 +512,11 @@ static inline int xsm_hvm_param (xsm_default_t def, struct 
domain *d, unsigned l
     return xsm_ops->hvm_param(d, op);
 }
 
+static inline int xsm_hvm_param_nested (xsm_default_t def, struct domain *d)
+{
+    return xsm_ops->hvm_param_nested(d);
+}
+
 #ifdef CONFIG_X86
 static inline int xsm_shadow_control (xsm_default_t def, struct domain *d, 
uint32_t op)
 {
diff --git a/xen/xsm/dummy.c b/xen/xsm/dummy.c
index 7235d82..49f4fb8 100644
--- a/xen/xsm/dummy.c
+++ b/xen/xsm/dummy.c
@@ -104,6 +104,7 @@ void xsm_fixup_ops (struct xsm_operations *ops)
     set_to_dummy_if_null(ops, tmem_op);
     set_to_dummy_if_null(ops, tmem_control);
     set_to_dummy_if_null(ops, hvm_param);
+    set_to_dummy_if_null(ops, hvm_param_nested);
 
     set_to_dummy_if_null(ops, do_xsm_op);
 
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index ca42891..7909ad5 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1107,6 +1107,11 @@ static int flask_hvm_param(struct domain *d, unsigned 
long op)
     return current_has_perm(d, SECCLASS_HVM, perm);
 }
 
+static int flask_hvm_param_nested(struct domain *d)
+{
+    return current_has_perm(d, SECCLASS_HVM, HVM__NESTED);
+}
+
 #ifdef CONFIG_X86
 static int flask_shadow_control(struct domain *d, uint32_t op)
 {
@@ -1524,6 +1529,7 @@ static struct xsm_operations flask_ops = {
     .tmem_op = flask_tmem_op,
     .tmem_control = flask_tmem_control,
     .hvm_param = flask_hvm_param,
+    .hvm_param_nested = flask_hvm_param_nested,
 
     .do_xsm_op = do_flask_op,
 
diff --git a/xen/xsm/flask/policy/access_vectors 
b/xen/xsm/flask/policy/access_vectors
index 05bb52e..0b83fbb 100644
--- a/xen/xsm/flask/policy/access_vectors
+++ b/xen/xsm/flask/policy/access_vectors
@@ -242,6 +242,8 @@ class hvm
 #  source = domain whose memory is being shared
 #  target = client domain
     share_mem
+# HVMOP_set_param setting HVM_PARAM_NESTEDHVM
+    nested
 }
 
 # Class event describes event channels.  Interdomain event channels have their
-- 
1.8.1.4


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