tools/libxencalls: add new function to query hypercall buffer safety

Add a new function to query whether hypercall buffers are always safe
to access by the hypervisor or might result in EFAULT.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libs/call/Makefile

@@ -2,7 +2,7 @@ XEN_ROOT = $(CURDIR)/../../..
 include $(XEN_ROOT)/tools/Rules.mk
 
 MAJOR    = 1
-MINOR    = 0
+MINOR    = 1
 SHLIB_LDFLAGS += -Wl,--version-script=libxencall.map
 
 CFLAGS   += -Werror -Wmissing-prototypes

tools/libs/call/freebsd.c

@@ -107,6 +107,11 @@ void osdep_free_pages(xencall_handle *xcall, void *ptr, size_t npages)
     errno = saved_errno;
 }
 
+int xencall_buffers_never_fault(xencall_handle *xcall)
+{
+    return 1;
+}
+
 /*
  * Local variables:
  * mode: C

tools/libs/call/include/xencall.h

@@ -115,6 +115,13 @@ void xencall_free_buffer_pages(xencall_handle *xcall, void *p, size_t nr_pages);
 void *xencall_alloc_buffer(xencall_handle *xcall, size_t size);
 void xencall_free_buffer(xencall_handle *xcall, void *p);
 
+/*
+ * Are allocated hypercall buffers safe to be accessed by the hypervisor all
+ * the time?
+ * Returns 0 if EFAULT might be possible.
+ */
+int xencall_buffers_never_fault(xencall_handle *xcall);
+
 #endif
 
 /*

tools/libs/call/libxencall.map

@@ -17,3 +17,8 @@ VERS_1.0 {
 		xencall_free_buffer_pages;
 	local: *; /* Do not expose anything by default */
 };
+
+VERS_1.1 {
+	global:
+		xencall_buffers_never_fault;
+} VERS_1.0;

tools/libs/call/linux.c

@@ -171,6 +171,11 @@ void osdep_free_pages(xencall_handle *xcall, void *ptr, size_t npages)
     errno = saved_errno;
 }
 
+int xencall_buffers_never_fault(xencall_handle *xcall)
+{
+    return xcall->buf_fd >= 0;
+}
+
 /*
  * Local variables:
  * mode: C

tools/libs/call/minios.c

@@ -70,6 +70,11 @@ void osdep_free_pages(xencall_handle *xcall, void *ptr, size_t npages)
     free(ptr);
 }
 
+int xencall_buffers_never_fault(xencall_handle *xcall)
+{
+    return 1;
+}
+
 /*
  * Local variables:
  * mode: C

tools/libs/call/netbsd.c

@@ -110,6 +110,11 @@ int do_xen_hypercall(xencall_handle *xcall, privcmd_hypercall_t *hypercall)
         return hypercall->retval;
 }
 
+int xencall_buffers_never_fault(xencall_handle *xcall)
+{
+    return 1;
+}
+
 /*
  * Local variables:
  * mode: C

tools/libs/call/solaris.c

@@ -86,6 +86,11 @@ int do_xen_hypercall(xencall_handle *xcall, privcmd_hypercall_t *hypercall)
     return ioctl(fd, IOCTL_PRIVCMD_HYPERCALL, hypercall);
 }
 
+int xencall_buffers_never_fault(xencall_handle *xcall)
+{
+    return 1;
+}
+
 /*
  * Local variables:
  * mode: C