kernel: add K_INHERIT_PERMS flag

By default, threads are created only having access to their own thread
object and nothing else. This new flag to k_thread_create() gives the
thread access to all objects that the parent had at the time it was
created, with the exception of the parent thread itself.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

include/kernel.h

@@ -471,6 +471,12 @@ extern void k_call_stacks_analyze(void);
  */
 #define K_USER (1 << 2)
 
+/* Indicates that the thread being created should inherit all kernel object
+ * permissions from the thread that created it. No effect if CONFIG_USERSPACE
+ * is not enabled.
+ */
+#define K_INHERIT_PERMS (1 << 3)
+
 #ifdef CONFIG_X86
 /* x86 Bitmask definitions for threads user options */
 

include/linker/kobject-text.ld

@@ -2,14 +2,14 @@
 #if defined(CONFIG_DEBUG) || defined(CONFIG_STACK_CANARIES)
 #define KOBJECT_TEXT_AREA	256
 #else
-#define KOBJECT_TEXT_AREA	78
+#define KOBJECT_TEXT_AREA	118
 #endif
 #endif
 
 #ifdef CONFIG_USERSPACE
 	/* We need to reserve room for the gperf generated hash functions.
 	 * Fortunately, unlike the data tables, the size of the code is
-	 * reasonably predictable; on x86 usually about 44 bytes with -Os.
+	 * reasonably predictable.
 	 *
 	 * The linker will error out complaining that the location pointer
 	 * is moving backwards if the reserved room isn't large enough.
@@ -19,6 +19,7 @@
 	_kobject_text_area_end = .;
 #ifndef LINKER_PASS2
 	PROVIDE(_k_object_find = .);
+	PROVIDE(_k_object_wordlist_foreach = .);
 #endif
 	. += KOBJECT_TEXT_AREA - (_kobject_text_area_end - _kobject_text_area_start);
 #endif /* CONFIG_USERSPACE */

kernel/include/syscall_handler.h

@@ -63,6 +63,25 @@ extern void _dump_object_error(int retval, void *obj, struct _k_object *ko,
  */
 extern struct _k_object *_k_object_find(void *obj);
 
+typedef void (*_wordlist_cb_func_t)(struct _k_object *ko, void *context);
+
+/**
+ * Iterate over all the kernel object metadata in the system
+ *
+ * @param func function to run on each struct _k_object
+ * @param context Context pointer to pass to each invocation
+ */
+extern void _k_object_wordlist_foreach(_wordlist_cb_func_t func, void *context);
+
+/**
+ * Copy all kernel object permissions from the parent to the child
+ *
+ * @param parent Parent thread, to get permissions from
+ * @param child Child thread, to copy permissions to
+ */
+extern void _thread_perms_inherit(struct k_thread *parent,
+				  struct k_thread *child);
+
 /**
  * Grant a thread permission to a kernel object
  *

kernel/thread.c

@@ -286,6 +286,10 @@ void _setup_new_thread(struct k_thread *new_thread,
 
 	/* Any given thread has access to itself */
 	k_object_access_grant(new_thread, new_thread);
+
+	if (options & K_INHERIT_PERMS) {
+		_thread_perms_inherit(_current, new_thread);
+	}
 #endif
 }
 

kernel/userspace.c

@@ -92,6 +92,36 @@ const char *otype_to_str(enum k_objects otype)
 #endif
 }
 
+struct perm_ctx {
+	int parent_id;
+	int child_id;
+	struct k_thread *parent;
+};
+
+static void wordlist_cb(struct _k_object *ko, void *ctx_ptr)
+{
+	struct perm_ctx *ctx = (struct perm_ctx *)ctx_ptr;
+
+	if (sys_bitfield_test_bit((mem_addr_t)&ko->perms, ctx->parent_id) &&
+				  (struct k_thread *)ko->name != ctx->parent) {
+		sys_bitfield_set_bit((mem_addr_t)&ko->perms, ctx->child_id);
+	}
+}
+
+void _thread_perms_inherit(struct k_thread *parent, struct k_thread *child)
+{
+	struct perm_ctx ctx = {
+		parent->base.perm_index,
+		child->base.perm_index,
+		parent
+	};
+
+	if ((ctx.parent_id < 8 * CONFIG_MAX_THREAD_BYTES) &&
+	    (ctx.child_id < 8 * CONFIG_MAX_THREAD_BYTES)) {
+		_k_object_wordlist_foreach(wordlist_cb, &ctx);
+	}
+}
+
 void _thread_perms_set(struct _k_object *ko, struct k_thread *thread)
 {
 	if (thread->base.perm_index < 8 * CONFIG_MAX_THREAD_BYTES) {

scripts/gen_kobject_list.py

@@ -467,9 +467,11 @@ def find_kobjects(elf, syms):
 header = """%compare-lengths
 %define lookup-function-name _k_object_lookup
 %language=ANSI-C
+%global-table
 %struct-type
 %{
 #include <kernel.h>
+#include <syscall_handler.h>
 #include <string.h>
 %}
 struct _k_object;
@@ -485,6 +487,17 @@ struct _k_object *_k_object_find(void *obj)
 {
     return _k_object_lookup((const char *)obj, sizeof(void *));
 }
+
+void _k_object_wordlist_foreach(_wordlist_cb_func_t func, void *context)
+{
+    int i;
+
+    for (i = MIN_HASH_VALUE; i <= MAX_HASH_VALUE; i++) {
+        if (wordlist[i].name) {
+            func(&wordlist[i], context);
+        }
+    }
+}
 """