livepatch/arm64: fix arch specific alternative section

hulk inclusion
category: bugfix
bugzilla: 5507
CVE: NA

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

Override arch_klp_init_object_loaded() to perform additional
arch-specific tasks when a target module loads, such as applying
arch-specific sections. On arm64, we must apply per-object
.altinstructions sections when a target module loads.

These sections are prefixed with ".klp.arch.$objname.$secname",
so that they can be easily identified when iterating through
a patch module's Elf sections.

Fix next calltrace:
	livepatch: enabling patch 'livepatch_0001_test_per_cpu_cmdline'
	Unable to handle kernel paging request at virtual address ffff34dc4663e018
	pc : cmdline_proc_show+0x24/0xc40 [livepatch_0001_test_per_cpu_cmdline]
	lr : seq_read+0xd4/0x4a8
	sp : ffff0000d0a73c30
	Call trace:
	  cmdline_proc_show+0x24/0xc40 [livepatch_0001_test_per_cpu_cmdline]
	  seq_read+0xd4/0x4a8
	  proc_reg_read+0x80/0xd8
	  __vfs_read+0x60/0x188
	  vfs_read+0x94/0x150
	  ksys_read+0x74/0xf0
	  __arm64_sys_read+0x24/0x30
	  el0_svc_common+0xa0/0x180
	  el0_svc_handler+0x38/0x78
	  el0_svc+0x8/0xc
	  Code: d503201f f0274aa2 91006042 d538d083 (b8636842)
	---[ end trace 1256914246c5a0cf ]---

Testcase livepatch code:
	fs/proc/cmdline.c
	static int cmdline_proc_show(struct seq_file *m, void *v)
	{
	+	seq_printf(m, "[%d] ", raw_smp_processor_id());
		seq_puts(m, saved_command_line);
			seq_putc(m, '\n');
				return 0;
	}
Signed-off-by: NCheng Jian <cj.chengjian@huawei.com>
Reviewed-by: NBin Li <huawei.libin@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

arch/arm64/kernel/livepatch.c

@@ -344,3 +344,42 @@ int arch_klp_func_can_patch(struct klp_func *func)
 }
 #endif /* #ifdef CONFIG_ARM64_MODULE_PLTS */
 #endif
+
+
+/* Apply per-object alternatives. Based on arm64 module_finalize() */
+void arch_klp_init_object_loaded(struct klp_patch *patch,
+				 struct klp_object *obj)
+{
+	int cnt;
+	struct klp_modinfo *info;
+	Elf_Shdr *s, *alt = NULL;
+	void *aseg;
+	const char *objname;
+	char sec_objname[MODULE_NAME_LEN];
+	char secname[KSYM_NAME_LEN];
+
+	info = patch->mod->klp_info;
+	objname = obj->name ? obj->name : "vmlinux";
+
+	/* See livepatch core code for BUILD_BUG_ON() explanation */
+	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
+
+	for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
+		/* Apply per-object .klp.arch sections */
+		cnt = sscanf(info->secstrings + s->sh_name,
+			     ".klp.arch.%55[^.].%127s",
+			     sec_objname, secname);
+
+		if (cnt != 2)
+			continue;
+		if (strcmp(sec_objname, objname))
+			continue;
+		if (!strcmp(".altinstructions", secname))
+			alt = s;
+	}
+
+	if (alt) {
+		aseg = (void *) alt->sh_addr;
+		apply_alternatives_module(aseg, alt->sh_size);
+	}
+}