efi/libstub: arm64: support strchr function for EFI stub

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5J0X7
CVE: NA

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

Since arm64 does not use a builtin decompressor, the EFI stub is built
into the kernel proper. So instead, separate the contents of libstub
and its dependencies, by putting them into their own namespace by
prefixing all of its symbols with __efistub.This way, we have tight
control over what parts of the kernel proper are referenced by the stub.

Follow the rules and support strchr function for EFI stub, it will be
used to parse cmdline args.
Signed-off-by: NGaosheng Cui <cuigaosheng1@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/arm64/kernel/image-vars.h

@@ -35,6 +35,7 @@ __efistub_strnlen		= __pi_strnlen;
 __efistub_strcmp		= __pi_strcmp;
 __efistub_strncmp		= __pi_strncmp;
 __efistub_strrchr		= __pi_strrchr;
+__efistub_strchr		= __pi_strchr;
 __efistub___clean_dcache_area_poc = __pi___clean_dcache_area_poc;
 
 #ifdef CONFIG_KASAN

arch/arm64/lib/strchr.S

@@ -18,7 +18,7 @@
  * Returns:
  *	x0 - address of first occurrence of 'c' or 0
  */
-SYM_FUNC_START_WEAK(strchr)
+SYM_FUNC_START_WEAK_PI(strchr)
 	and	w1, w1, #0xff
 1:	ldrb	w2, [x0], #1
 	cmp	w2, w1
@@ -28,5 +28,5 @@ SYM_FUNC_START_WEAK(strchr)
 	cmp	w2, w1
 	csel	x0, x0, xzr, eq
 	ret
-SYM_FUNC_END(strchr)
+SYM_FUNC_END_PI(strchr)
 EXPORT_SYMBOL_NOKASAN(strchr)

drivers/firmware/efi/libstub/string.c

@@ -113,3 +113,21 @@ long simple_strtol(const char *cp, char **endp, unsigned int base)
 
 	return simple_strtoull(cp, endp, base);
 }
+
+#ifndef __HAVE_ARCH_STRCHR
+/**
+ * strchr - Find the first occurrence of a character in a string
+ * @s: The string to be searched
+ * @c: The character to search for
+ *
+ * Note that the %NUL-terminator is considered part of the string, and can
+ * be searched for.
+ */
+char *strchr(const char *s, int c)
+{
+	for (; *s != (char)c; ++s)
+		if (*s == '\0')
+			return NULL;
+	return (char *)s;
+}
+#endif