livepatch/arm64: support function force patched/unpatched

euler inclusion
category: feature
Bugzilla: 5507
CVE: N/A

----------------------------------------

Some functions in the kernel are always on the stack of some
thread in the system. Attempts to patch these function will
currently always fail the activeness safety check.

However, through human inspection, it can be determined that,
for a particular function, consistency is maintained even if
the old and new versions of the function run concurrently.

commit 2e93c5e1e3dc ("support forced patching") in kpatch-build
introduces a KPATCH_FORCE_UNSAFE() macro to define patched
functions that such be exempted from the activeness safety
check. now kernel implement this feature.
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>
Reviewed-by: NLi Bin <huawei.libin@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/arm64/kernel/livepatch.c

@@ -77,6 +77,8 @@ static int klp_check_activeness_func(struct stackframe *frame, void *data)
 	for (obj = patch->objs; obj->funcs; obj++) {
 		for (func = obj->funcs; func->old_name; func++) {
 			if (args->enable) {
+				if (func->force)
+					continue;
 				func_addr = func->old_addr;
 				func_size = func->old_size;
 			} else {

include/linux/livepatch.h

@@ -75,6 +75,7 @@ struct klp_func {
 	 * in kallsyms for the given object is used.
 	 */
 	unsigned long old_sympos;
+	int force;
 
 	/* internal */
 	unsigned long old_addr;