Re: [Xen-devel] [PATCH] xen: additionally restrict xenforeignmemory operations

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 24 Mar 2017, Paul Durrant wrote:
> Commit f0f272baf3a7 "xen: use libxendevice model to restrict operations"
> added a command-line option (-xen-domid-restrict) to limit operations
> using the libxendevicemodel API to a specified domid. The commit also
> noted that the restriction would be extended to cover operations issued
> via other xen libraries by subsequent patches.
> 
> My recent Xen patch [1] added a call to the xenforeignmemory API to allow
> it to be restricted. This patch now makes use of that new call when the
> -xen-domid-restrict option is passed.
> 
> [1] http://xenbits.xen.org/gitweb/?p=xen.git;a=commit;h=5823d6eb
> 
> Signed-off-by: Paul Durrant <paul.durrant@xxxxxxxxxx>
> ---
> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>
> ---
>  include/hw/xen/xen_common.h | 52 
> +++++++++++++++++++++++++++++++++------------
>  1 file changed, 39 insertions(+), 13 deletions(-)
> 
> diff --git a/include/hw/xen/xen_common.h b/include/hw/xen/xen_common.h
> index 4f3bd35..6f13e8c 100644
> --- a/include/hw/xen/xen_common.h
> +++ b/include/hw/xen/xen_common.h
> @@ -213,19 +213,6 @@ static inline int xen_modified_memory(domid_t domid, 
> uint64_t first_pfn,
>      return xendevicemodel_modified_memory(xen_dmod, domid, first_pfn, nr);
>  }
>  
> -static inline int xen_restrict(domid_t domid)
> -{
> -    int rc = xendevicemodel_restrict(xen_dmod, domid);
> -
> -    trace_xen_domid_restrict(errno);
> -
> -    if (errno == ENOTTY) {
> -        return 0;
> -    }
> -
> -    return rc;
> -}
> -
>  /* Xen 4.2 through 4.6 */
>  #if CONFIG_XEN_CTRL_INTERFACE_VERSION < 40701
>  
> @@ -276,8 +263,47 @@ static inline void *xenforeignmemory_map(xc_interface 
> *h, uint32_t dom,
>  
>  #endif
>  
> +#if CONFIG_XEN_CTRL_INTERFACE_VERSION < 40900
> +
> +static inline int xenforeignmemory_restrict(
> +    xenforeignmemory_handle *fmem, domid_t domid)
> +{
> +    errno = ENOTTY;
> +    return -1;
> +}
> +
> +#endif
> +
>  extern xenforeignmemory_handle *xen_fmem;
>  
> +static inline int xen_restrict(domid_t domid)
> +{
> +    int rc;
> +
> +    /* Attempt to restrict devicemodel operations */
> +    rc = xendevicemodel_restrict(xen_dmod, domid);
> +    trace_xen_domid_restrict(rc ? errno : 0);
> +
> +    if (rc < 0) {
> +        /*
> +         * If errno is ENOTTY then restriction is not implemented so
> +         * there's no point in trying to restrict other types of
> +         * operation, but it should not be treated as a failure.
> +         */
> +        if (errno == ENOTTY) {
> +            return 0;
> +        }
> +
> +        return rc;
> +    }
> +
> +    /* Restrict foreignmemory operations */
> +    rc = xenforeignmemory_restrict(xen_fmem, domid);
> +    trace_xen_domid_restrict(rc ? errno : 0);
> +
> +    return rc;
> +}
> +
>  void destroy_hvm_domain(bool reboot);
>  
>  /* shutdown/destroy current domain because of an error */

This is OK but the file is growing too entangled. What do you think of
the following, which moves the if CONFIG_XEN_CTRL_INTERFACE_VERSION <
40701 at the top? This way we don't have to add yet another ifdef.

diff --git a/include/hw/xen/xen_common.h b/include/hw/xen/xen_common.h
index 4f3bd35..624fb86 100644
--- a/include/hw/xen/xen_common.h
+++ b/include/hw/xen/xen_common.h
@@ -27,6 +27,58 @@ extern xc_interface *xen_xc;
  * We don't support Xen prior to 4.2.0.
  */
 
+/* Xen 4.2 through 4.6 */
+#if CONFIG_XEN_CTRL_INTERFACE_VERSION < 40701
+
+typedef xc_interface xenforeignmemory_handle;
+typedef xc_evtchn xenevtchn_handle;
+typedef xc_gnttab xengnttab_handle;
+
+#define xenevtchn_open(l, f) xc_evtchn_open(l, f);
+#define xenevtchn_close(h) xc_evtchn_close(h)
+#define xenevtchn_fd(h) xc_evtchn_fd(h)
+#define xenevtchn_pending(h) xc_evtchn_pending(h)
+#define xenevtchn_notify(h, p) xc_evtchn_notify(h, p)
+#define xenevtchn_bind_interdomain(h, d, p) xc_evtchn_bind_interdomain(h, d, p)
+#define xenevtchn_unmask(h, p) xc_evtchn_unmask(h, p)
+#define xenevtchn_unbind(h, p) xc_evtchn_unbind(h, p)
+
+#define xengnttab_open(l, f) xc_gnttab_open(l, f)
+#define xengnttab_close(h) xc_gnttab_close(h)
+#define xengnttab_set_max_grants(h, n) xc_gnttab_set_max_grants(h, n)
+#define xengnttab_map_grant_ref(h, d, r, p) xc_gnttab_map_grant_ref(h, d, r, p)
+#define xengnttab_unmap(h, a, n) xc_gnttab_munmap(h, a, n)
+#define xengnttab_map_grant_refs(h, c, d, r, p) \
+    xc_gnttab_map_grant_refs(h, c, d, r, p)
+#define xengnttab_map_domain_grant_refs(h, c, d, r, p) \
+    xc_gnttab_map_domain_grant_refs(h, c, d, r, p)
+
+#define xenforeignmemory_open(l, f) xen_xc
+#define xenforeignmemory_close(h)
+
+static inline void *xenforeignmemory_map(xc_interface *h, uint32_t dom,
+                                         int prot, size_t pages,
+                                         const xen_pfn_t arr[/*pages*/],
+                                         int err[/*pages*/])
+{
+    if (err)
+        return xc_map_foreign_bulk(h, dom, prot, arr, err, pages);
+    else
+        return xc_map_foreign_pages(h, dom, prot, arr, pages);
+}
+
+#define xenforeignmemory_unmap(h, p, s) munmap(p, s * XC_PAGE_SIZE)
+
+#else /* CONFIG_XEN_CTRL_INTERFACE_VERSION >= 40701 */
+
+#include <xenevtchn.h>
+#include <xengnttab.h>
+#include <xenforeignmemory.h>
+
+#endif
+
+extern xenforeignmemory_handle *xen_fmem;
+
 #if CONFIG_XEN_CTRL_INTERFACE_VERSION < 40900
 
 typedef xc_interface xendevicemodel_handle;
@@ -159,6 +211,13 @@ static inline int xendevicemodel_restrict(
     return -1;
 }
 
+static inline int xenforeignmemory_restrict(
+    xenforeignmemory_handle *fmem, domid_t domid)
+{
+    errno = ENOTTY;
+    return -1;
+}
+
 #else /* CONFIG_XEN_CTRL_INTERFACE_VERSION >= 40900 */
 
 #include <xendevicemodel.h>
@@ -215,69 +274,32 @@ static inline int xen_modified_memory(domid_t domid, 
uint64_t first_pfn,
 
 static inline int xen_restrict(domid_t domid)
 {
-    int rc = xendevicemodel_restrict(xen_dmod, domid);
+    int rc;
 
-    trace_xen_domid_restrict(errno);
+    /* Attempt to restrict devicemodel operations */
+    rc = xendevicemodel_restrict(xen_dmod, domid);
+    trace_xen_domid_restrict(rc ? errno : 0);
 
-    if (errno == ENOTTY) {
-        return 0;
+    if (rc < 0) {
+        /*
+         * If errno is ENOTTY then restriction is not implemented so
+         * there's no point in trying to restrict other types of
+         * operation, but it should not be treated as a failure.
+         */
+        if (errno == ENOTTY) {
+            return 0;
+        }
+
+        return rc;
     }
 
-    return rc;
-}
-
-/* Xen 4.2 through 4.6 */
-#if CONFIG_XEN_CTRL_INTERFACE_VERSION < 40701
-
-typedef xc_interface xenforeignmemory_handle;
-typedef xc_evtchn xenevtchn_handle;
-typedef xc_gnttab xengnttab_handle;
-
-#define xenevtchn_open(l, f) xc_evtchn_open(l, f);
-#define xenevtchn_close(h) xc_evtchn_close(h)
-#define xenevtchn_fd(h) xc_evtchn_fd(h)
-#define xenevtchn_pending(h) xc_evtchn_pending(h)
-#define xenevtchn_notify(h, p) xc_evtchn_notify(h, p)
-#define xenevtchn_bind_interdomain(h, d, p) xc_evtchn_bind_interdomain(h, d, p)
-#define xenevtchn_unmask(h, p) xc_evtchn_unmask(h, p)
-#define xenevtchn_unbind(h, p) xc_evtchn_unbind(h, p)
-
-#define xengnttab_open(l, f) xc_gnttab_open(l, f)
-#define xengnttab_close(h) xc_gnttab_close(h)
-#define xengnttab_set_max_grants(h, n) xc_gnttab_set_max_grants(h, n)
-#define xengnttab_map_grant_ref(h, d, r, p) xc_gnttab_map_grant_ref(h, d, r, p)
-#define xengnttab_unmap(h, a, n) xc_gnttab_munmap(h, a, n)
-#define xengnttab_map_grant_refs(h, c, d, r, p) \
-    xc_gnttab_map_grant_refs(h, c, d, r, p)
-#define xengnttab_map_domain_grant_refs(h, c, d, r, p) \
-    xc_gnttab_map_domain_grant_refs(h, c, d, r, p)
-
-#define xenforeignmemory_open(l, f) xen_xc
-#define xenforeignmemory_close(h)
+    /* Restrict foreignmemory operations */
+    rc = xenforeignmemory_restrict(xen_fmem, domid);
+    trace_xen_domid_restrict(rc ? errno : 0);
 
-static inline void *xenforeignmemory_map(xc_interface *h, uint32_t dom,
-                                         int prot, size_t pages,
-                                         const xen_pfn_t arr[/*pages*/],
-                                         int err[/*pages*/])
-{
-    if (err)
-        return xc_map_foreign_bulk(h, dom, prot, arr, err, pages);
-    else
-        return xc_map_foreign_pages(h, dom, prot, arr, pages);
+    return rc;
 }
 
-#define xenforeignmemory_unmap(h, p, s) munmap(p, s * XC_PAGE_SIZE)
-
-#else /* CONFIG_XEN_CTRL_INTERFACE_VERSION >= 40701 */
-
-#include <xenevtchn.h>
-#include <xengnttab.h>
-#include <xenforeignmemory.h>
-
-#endif
-
-extern xenforeignmemory_handle *xen_fmem;
-
 void destroy_hvm_domain(bool reboot);
 
 /* shutdown/destroy current domain because of an error */

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