LoongArch: Add basic STACKPROTECTOR support

Add basic stack protector support similar to other architectures. A
constant canary value is set at boot time, and with help of compiler's
-fstack-protector we can detect stack corruption.

Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/Kconfig

@@ -103,6 +103,7 @@ config LOONGARCH
 	select HAVE_REGS_AND_STACK_ACCESS_API
 	select HAVE_RSEQ
 	select HAVE_SETUP_PER_CPU_AREA if NUMA
+	select HAVE_STACKPROTECTOR
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_TIF_NOHZ
 	select HAVE_VIRT_CPU_ACCOUNTING_GEN if !SMP

arch/loongarch/include/asm/stackprotector.h

@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * GCC stack protector support.
+ *
+ * Stack protector works by putting predefined pattern at the start of
+ * the stack frame and verifying that it hasn't been overwritten when
+ * returning from the function. The pattern is called stack canary and
+ * on LoongArch gcc expects it to be defined by a global variable called
+ * "__stack_chk_guard".
+ */
+
+#ifndef _ASM_STACKPROTECTOR_H
+#define _ASM_STACKPROTECTOR_H
+
+#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;
+
+	current->stack_canary = canary;
+	__stack_chk_guard = current->stack_canary;
+}
+
+#endif	/* _ASM_STACKPROTECTOR_H */

arch/loongarch/kernel/asm-offsets.c

@@ -68,6 +68,9 @@ void output_task_defines(void)
 	OFFSET(TASK_FLAGS, task_struct, flags);
 	OFFSET(TASK_MM, task_struct, mm);
 	OFFSET(TASK_PID, task_struct, pid);
+#if defined(CONFIG_STACKPROTECTOR)
+	OFFSET(TASK_STACK_CANARY, task_struct, stack_canary);
+#endif
 	DEFINE(TASK_STRUCT_SIZE, sizeof(struct task_struct));
 	BLANK();
 }

arch/loongarch/kernel/process.c

@@ -47,6 +47,12 @@
 #include <asm/unwind.h>
 #include <asm/vdso.h>
 
+#ifdef CONFIG_STACKPROTECTOR
+#include <linux/stackprotector.h>
+unsigned long __stack_chk_guard __read_mostly;
+EXPORT_SYMBOL(__stack_chk_guard);
+#endif
+
 /*
  * Idle related variables and functions
  */

arch/loongarch/kernel/switch.S

@@ -23,6 +23,11 @@ SYM_FUNC_START(__switch_to)
 	stptr.d	ra, a0, THREAD_REG01
 	stptr.d a3, a0, THREAD_SCHED_RA
 	stptr.d a4, a0, THREAD_SCHED_CFA
+#if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
+	la	t7, __stack_chk_guard
+	LONG_L	t8, a1, TASK_STACK_CANARY
+	LONG_S	t8, t7, 0
+#endif
 	move	tp, a2
 	cpu_restore_nonscratch a1