[PATCH v4 0/2] Adds starting the idle domain privileged

[PATCH v4 0/2] Adds starting the idle domain privileged

[Daniel P. Smith]

This series makes it so that the idle domain is started privileged under the
default policy, which the SILO policy inherits, and under the flask policy. It
then introduces a new one-way XSM hook, xsm_transition_running, that is hooked
by an XSM policy to transition the idle domain to its running privilege level.

Changes in v4:
- reworded patch 1 commit messaged
- fixed whitespace to coding style
- fixed comment to coding style

Changes in v3:
- renamed *_transition_running() to *_set_system_active()
- changed the XSM hook set_system_active() from void to int return
- added ASSERT check for the expected privilege level each XSM policy expected
- replaced a check against is_privileged in each arch with checking the return
  value from the call to xsm_set_system_active()

Changes in v2:
- renamed flask_domain_runtime_security() to flask_transition_running()
- added the missed assignment of self_sid

Daniel P. Smith (2):
  xsm: create idle domain privileged and demote after setup
  flask: implement xsm_set_system_active

 tools/flask/policy/modules/xen.if      |  6 ++++++
 tools/flask/policy/modules/xen.te      |  1 +
 tools/flask/policy/policy/initial_sids |  1 +
 xen/arch/arm/setup.c                   |  3 +++
 xen/arch/x86/setup.c                   |  3 +++
 xen/common/sched/core.c                |  7 ++++++-
 xen/include/xsm/dummy.h                | 17 +++++++++++++++
 xen/include/xsm/xsm.h                  |  6 ++++++
 xen/xsm/dummy.c                        |  1 +
 xen/xsm/flask/hooks.c                  | 29 +++++++++++++++++++++++++-
 xen/xsm/flask/policy/initial_sids      |  1 +
 11 files changed, 73 insertions(+), 2 deletions(-)

-- 
2.20.1

[PATCH v4 1/2] xsm: create idle domain privileged and demote after setup

[Daniel P. Smith]

There are new capabilities, dom0less and hyperlaunch, that introduce internal
hypervisor logic which needs to make resource allocation calls that are
protected by XSM access checks. This creates an issue as a subset of the
hypervisor code is executed under a system domain, the idle domain, that is
represented by a per-CPU non-privileged struct domain. To enable these new
capabilities to function correctly but in a controlled manner, this commit
changes the idle system domain to be created as a privileged domain under the
default policy and demoted before transitioning to running. A new XSM hook,
xsm_set_system_active(), is introduced to allow each XSM policy type to demote
the idle domain appropriately for that policy type. In the case of SILO, it
inherits the default policy's hook for xsm_set_system_active().

For flask a stub is added to ensure that flask policy system will function
correctly with this patch until flask is extended with support for starting the
idle domain privileged and properly demoting it on the call to
xsm_set_system_active().

Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>
---
 xen/arch/arm/setup.c    |  3 +++
 xen/arch/x86/setup.c    |  3 +++
 xen/common/sched/core.c |  7 ++++++-
 xen/include/xsm/dummy.h | 17 +++++++++++++++++
 xen/include/xsm/xsm.h   |  6 ++++++
 xen/xsm/dummy.c         |  1 +
 xen/xsm/flask/hooks.c   | 21 +++++++++++++++++++++
 7 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index d5d0792ed4..dc0bdef6b7 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -1048,6 +1048,9 @@ void __init start_xen(unsigned long boot_phys_offset,
     /* Hide UART from DOM0 if we're using it */
     serial_endboot();
 
+    if ( xsm_set_system_active() != 0 )
+        panic("xsm: unable to set hypervisor to SYSTEM_ACTIVE privilege\n");
+
     system_state = SYS_STATE_active;
 
     for_each_domain( d )
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 6f20e17892..e7a0ac9183 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -621,6 +621,9 @@ static void noreturn init_done(void)
     void *va;
     unsigned long start, end;
 
+    if ( xsm_set_system_active() != 0 )
+        panic("xsm: unable to set hypervisor to SYSTEM_ACTIVE privilege\n");
+
     system_state = SYS_STATE_active;
 
     domain_unpause_by_systemcontroller(dom0);
diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
index 19ab678181..7b1c03a0e1 100644
--- a/xen/common/sched/core.c
+++ b/xen/common/sched/core.c
@@ -3021,7 +3021,12 @@ void __init scheduler_init(void)
         sched_ratelimit_us = SCHED_DEFAULT_RATELIMIT_US;
     }
 
-    idle_domain = domain_create(DOMID_IDLE, NULL, 0);
+    /*
+     * The idle dom is created privileged to ensure unrestricted access during
+     * setup and will be demoted by xsm_set_system_active() when setup is
+     * complete.
+     */
+    idle_domain = domain_create(DOMID_IDLE, NULL, CDF_privileged);
     BUG_ON(IS_ERR(idle_domain));
     BUG_ON(nr_cpu_ids > ARRAY_SIZE(idle_vcpu));
     idle_domain->vcpu = idle_vcpu;
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 58afc1d589..3291fb5396 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -101,6 +101,23 @@ static always_inline int xsm_default_action(
     }
 }
 
+static XSM_INLINE int cf_check xsm_set_system_active(void)
+{
+    struct domain *d = current->domain;
+
+    ASSERT(d->is_privileged);
+
+    if ( d->domain_id != DOMID_IDLE )
+    {
+        printk("xsm_set_system_active: should only be called by idle domain\n");
+        return -EPERM;
+    }
+
+    d->is_privileged = false;
+
+    return 0;
+}
+
 static XSM_INLINE void cf_check xsm_security_domaininfo(
     struct domain *d, struct xen_domctl_getdomaininfo *info)
 {
diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
index 3e2b7fe3db..8dad03fd3d 100644
--- a/xen/include/xsm/xsm.h
+++ b/xen/include/xsm/xsm.h
@@ -52,6 +52,7 @@ typedef enum xsm_default xsm_default_t;
  * !!! WARNING !!!
  */
 struct xsm_ops {
+    int (*set_system_active)(void);
     void (*security_domaininfo)(struct domain *d,
                                 struct xen_domctl_getdomaininfo *info);
     int (*domain_create)(struct domain *d, uint32_t ssidref);
@@ -208,6 +209,11 @@ extern struct xsm_ops xsm_ops;
 
 #ifndef XSM_NO_WRAPPERS
 
+static inline int xsm_set_system_active(void)
+{
+    return alternative_call(xsm_ops.set_system_active);
+}
+
 static inline void xsm_security_domaininfo(
     struct domain *d, struct xen_domctl_getdomaininfo *info)
 {
diff --git a/xen/xsm/dummy.c b/xen/xsm/dummy.c
index 8c044ef615..e6ffa948f7 100644
--- a/xen/xsm/dummy.c
+++ b/xen/xsm/dummy.c
@@ -14,6 +14,7 @@
 #include <xsm/dummy.h>
 
 static const struct xsm_ops __initconst_cf_clobber dummy_ops = {
+    .set_system_active             = xsm_set_system_active,
     .security_domaininfo           = xsm_security_domaininfo,
     .domain_create                 = xsm_domain_create,
     .getdomaininfo                 = xsm_getdomaininfo,
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 0bf63ffa84..8a62de2fd6 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -186,6 +186,26 @@ static int cf_check flask_domain_alloc_security(struct domain *d)
     return 0;
 }
 
+static int cf_check flask_set_system_active(void)
+{
+    struct domain *d = current->domain;
+
+    if ( d->domain_id != DOMID_IDLE )
+    {
+        printk("xsm_set_system_active should only be called by idle domain\n");
+        return -EPERM;
+    }
+
+    /*
+     * While is_privileged has no significant meaning under flask, set to false
+     * as there are times in hypervisor code privilege checks check this
+     * directly instead of going through XSM.
+     */
+    d->is_privileged = false;
+
+    return 0;
+}
+
 static void cf_check flask_domain_free_security(struct domain *d)
 {
     struct domain_security_struct *dsec = d->ssid;
@@ -1766,6 +1786,7 @@ static int cf_check flask_argo_send(
 #endif
 
 static const struct xsm_ops __initconst_cf_clobber flask_ops = {
+    .set_system_active = flask_set_system_active,
     .security_domaininfo = flask_security_domaininfo,
     .domain_create = flask_domain_create,
     .getdomaininfo = flask_getdomaininfo,
-- 
2.20.1

Re: [PATCH v4 1/2] xsm: create idle domain privileged and demote after setup

[Jan Beulich]

On 25.04.2022 19:22, Daniel P. Smith wrote:
> --- a/xen/arch/x86/setup.c
> +++ b/xen/arch/x86/setup.c
> @@ -621,6 +621,9 @@ static void noreturn init_done(void)
>      void *va;
>      unsigned long start, end;
>  
> +    if ( xsm_set_system_active() != 0 )
> +        panic("xsm: unable to set hypervisor to SYSTEM_ACTIVE privilege\n");

Roger did request that the panic() either also report the error
code, or that the function be returning bool. You did neither,
and your earlier verbal reply also didn't really respond to this
part of Roger's comments.

> --- a/xen/xsm/flask/hooks.c
> +++ b/xen/xsm/flask/hooks.c
> @@ -186,6 +186,26 @@ static int cf_check flask_domain_alloc_security(struct domain *d)
>      return 0;
>  }
>  
> +static int cf_check flask_set_system_active(void)
> +{
> +    struct domain *d = current->domain;
> +
> +    if ( d->domain_id != DOMID_IDLE )
> +    {
> +        printk("xsm_set_system_active should only be called by idle domain\n");
> +        return -EPERM;
> +    }
> +
> +    /*
> +     * While is_privileged has no significant meaning under flask, set to false
> +     * as there are times in hypervisor code privilege checks check this
> +     * directly instead of going through XSM.
> +     */

It feels as if there is "which" missing between "checks" and "check",
or something else (better fitting "as there are times"), without which
the sentence is a little hard to follow.

Jan

Re: [PATCH v4 1/2] xsm: create idle domain privileged and demote after setup

[Daniel P. Smith]

On 4/26/22 02:35, Jan Beulich wrote:
> On 25.04.2022 19:22, Daniel P. Smith wrote:
>> --- a/xen/arch/x86/setup.c
>> +++ b/xen/arch/x86/setup.c
>> @@ -621,6 +621,9 @@ static void noreturn init_done(void)
>>       void *va;
>>       unsigned long start, end;
>>   
>> +    if ( xsm_set_system_active() != 0 )
>> +        panic("xsm: unable to set hypervisor to SYSTEM_ACTIVE privilege\n");
> 
> Roger did request that the panic() either also report the error
> code, or that the function be returning bool. You did neither,
> and your earlier verbal reply also didn't really respond to this
> part of Roger's comments.

Opps, my apologies. I meant to add his suggestion of adding the error to 
the panic message.

>> --- a/xen/xsm/flask/hooks.c
>> +++ b/xen/xsm/flask/hooks.c
>> @@ -186,6 +186,26 @@ static int cf_check flask_domain_alloc_security(struct domain *d)
>>       return 0;
>>   }
>>   
>> +static int cf_check flask_set_system_active(void)
>> +{
>> +    struct domain *d = current->domain;
>> +
>> +    if ( d->domain_id != DOMID_IDLE )
>> +    {
>> +        printk("xsm_set_system_active should only be called by idle domain\n");
>> +        return -EPERM;
>> +    }
>> +
>> +    /*
>> +     * While is_privileged has no significant meaning under flask, set to false
>> +     * as there are times in hypervisor code privilege checks check this
>> +     * directly instead of going through XSM.
>> +     */
> 
> It feels as if there is "which" missing between "checks" and "check",
> or something else (better fitting "as there are times"), without which
> the sentence is a little hard to follow.

You are correct, will fix.

v/r
dps

[PATCH v4 2/2] flask: implement xsm_set_system_active

[Daniel P. Smith]

This commit implements full support for starting the idle domain privileged by
introducing a new flask label xenboot_t which the idle domain is labeled with
at creation.  It then provides the implementation for the XSM hook
xsm_set_system_active to relabel the idle domain to the existing xen_t flask
label.

In the reference flask policy a new macro, xen_build_domain(target), is
introduced for creating policies for dom0less/hyperlaunch allowing the
hypervisor to create and assign the necessary resources for domain
construction.

Signed-off-by: Daniel P. Smith <dpsmith@apertussolutions.com>
Reviewed-by: Jason Andryuk <jandryuk@gmail.com>
---
 tools/flask/policy/modules/xen.if      | 6 ++++++
 tools/flask/policy/modules/xen.te      | 1 +
 tools/flask/policy/policy/initial_sids | 1 +
 xen/xsm/flask/hooks.c                  | 8 +++++++-
 xen/xsm/flask/policy/initial_sids      | 1 +
 5 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/flask/policy/modules/xen.if b/tools/flask/policy/modules/xen.if
index 5e2aa472b6..4ec676fff1 100644
--- a/tools/flask/policy/modules/xen.if
+++ b/tools/flask/policy/modules/xen.if
@@ -62,6 +62,12 @@ define(`create_domain_common', `
 			setparam altp2mhvm altp2mhvm_op dm };
 ')
 
+# xen_build_domain(target)
+#   Allow a domain to be created at boot by the hypervisor
+define(`xen_build_domain', `
+	allow xenboot_t $1_channel:event create;
+')
+
 # create_domain(priv, target)
 #   Allow a domain to be created directly
 define(`create_domain', `
diff --git a/tools/flask/policy/modules/xen.te b/tools/flask/policy/modules/xen.te
index 3dbf93d2b8..de98206fdd 100644
--- a/tools/flask/policy/modules/xen.te
+++ b/tools/flask/policy/modules/xen.te
@@ -24,6 +24,7 @@ attribute mls_priv;
 ################################################################################
 
 # The hypervisor itself
+type xenboot_t, xen_type, mls_priv;
 type xen_t, xen_type, mls_priv;
 
 # Domain 0
diff --git a/tools/flask/policy/policy/initial_sids b/tools/flask/policy/policy/initial_sids
index 6b7b7eff21..ec729d3ba3 100644
--- a/tools/flask/policy/policy/initial_sids
+++ b/tools/flask/policy/policy/initial_sids
@@ -2,6 +2,7 @@
 # objects created before the policy is loaded or for objects that do not have a
 # label defined in some other manner.
 
+sid xenboot gen_context(system_u:system_r:xenboot_t,s0)
 sid xen gen_context(system_u:system_r:xen_t,s0)
 sid dom0 gen_context(system_u:system_r:dom0_t,s0)
 sid domxen gen_context(system_u:system_r:domxen_t,s0)
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 8a62de2fd6..92eb12ddb1 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -168,7 +168,7 @@ static int cf_check flask_domain_alloc_security(struct domain *d)
     switch ( d->domain_id )
     {
     case DOMID_IDLE:
-        dsec->sid = SECINITSID_XEN;
+        dsec->sid = SECINITSID_XENBOOT;
         break;
     case DOMID_XEN:
         dsec->sid = SECINITSID_DOMXEN;
@@ -188,8 +188,12 @@ static int cf_check flask_domain_alloc_security(struct domain *d)
 
 static int cf_check flask_set_system_active(void)
 {
+    struct domain_security_struct *dsec;
     struct domain *d = current->domain;
 
+    dsec = d->ssid;
+    ASSERT(dsec->sid == SECINITSID_XENBOOT);
+
     if ( d->domain_id != DOMID_IDLE )
     {
         printk("xsm_set_system_active should only be called by idle domain\n");
@@ -203,6 +207,8 @@ static int cf_check flask_set_system_active(void)
      */
     d->is_privileged = false;
 
+    dsec->self_sid = dsec->sid = SECINITSID_XEN;
+
     return 0;
 }
 
diff --git a/xen/xsm/flask/policy/initial_sids b/xen/xsm/flask/policy/initial_sids
index 7eca70d339..e8b55b8368 100644
--- a/xen/xsm/flask/policy/initial_sids
+++ b/xen/xsm/flask/policy/initial_sids
@@ -3,6 +3,7 @@
 #
 # Define initial security identifiers 
 #
+sid xenboot
 sid xen
 sid dom0
 sid domio
-- 
2.20.1