csky: Initial stack protector support

This is a basic -fstack-protector support without per-task canary
switching. The protector will report something like when stack
corruption is detected:

It's tested with strcpy local array overflow in sys_kill and get:
stack-protector: Kernel stack is corrupted in: sys_kill+0x23c/0x23c

TODO:
 - Support task switch for different cannary
Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/Kconfig

@@ -49,6 +49,7 @@ config CSKY
 	select HAVE_PERF_USER_STACK_DUMP
 	select HAVE_DMA_API_DEBUG
 	select HAVE_DMA_CONTIGUOUS
+	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select MAY_HAVE_SPARSE_IRQ
 	select MODULES_USE_ELF_RELA if MODULES

arch/csky/include/asm/stackprotector.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H 1
+
+#include <linux/random.h>
+#include <linux/version.h>
+
+extern unsigned long __stack_chk_guard;
+
+/*
+ * Initialize the stackprotector canary value.
+ *
+ * NOTE: this must only be called from functions that never return,
+ * and it must always be inlined.
+ */
+static __always_inline void boot_init_stack_canary(void)
+{
+	unsigned long canary;
+
+	/* Try to get a semi random initial value. */
+	get_random_bytes(&canary, sizeof(canary));
+	canary ^= LINUX_VERSION_CODE;
+	canary &= CANARY_MASK;
+
+	current->stack_canary = canary;
+	__stack_chk_guard = current->stack_canary;
+}
+
+#endif /* __ASM_SH_STACKPROTECTOR_H */

arch/csky/kernel/process.c

@@ -16,6 +16,12 @@
 
 struct cpuinfo_csky cpu_data[NR_CPUS];
 
+#ifdef CONFIG_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
 asmlinkage void ret_from_fork(void);
 asmlinkage void ret_from_kernel_thread(void);