riscv: stacktrace: Disable KASAN checks for non-current tasks

Unwinding the stack of a task other than current, KASAN would report
"BUG: KASAN: out-of-bounds in walk_stackframe+0x41c/0x460"

There is a same issue on x86 and has been resolved by the commit
8493611 ("x86/unwind: Disable KASAN checks for non-current tasks")
The solution could be applied to RISC-V too.

This patch also can solve the issue:
https://seclists.org/oss-sec/2025/q4/23

Fixes: 5d8544e ("RISC-V: Generic library routines and assembly")
Co-developed-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Jiakai Xu <xujiakai2025@iscas.ac.cn>
Signed-off-by: Chunyan Zhang <zhangchunyan@iscas.ac.cn>
Link: https://lore.kernel.org/r/20251022072608.743484-1-zhangchunyan@iscas.ac.cn
[pjw@kernel.org: clean up checkpatch issues]
Signed-off-by: Paul Walmsley <pjw@kernel.org>

Author: Chunyan Zhang

arch/riscv/kernel/stacktrace.c

@@ -16,6 +16,22 @@
 
 #ifdef CONFIG_FRAME_POINTER
 
+/*
+ * This disables KASAN checking when reading a value from another task's stack,
+ * since the other task could be running on another CPU and could have poisoned
+ * the stack in the meantime.
+ */
+#define READ_ONCE_TASK_STACK(task, x)			\
+({							\
+	unsigned long val;				\
+	unsigned long addr = x;				\
+	if ((task) == current)				\
+		val = READ_ONCE(addr);			\
+	else						\
+		val = READ_ONCE_NOCHECK(addr);		\
+	val;						\
+})
+
 extern asmlinkage void handle_exception(void);
 extern unsigned long ret_from_exception_end;
 
@@ -69,8 +85,9 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
 			fp = frame->ra;
 			pc = regs->ra;
 		} else {
-			fp = frame->fp;
-			pc = ftrace_graph_ret_addr(current, &graph_idx, frame->ra,
+			fp = READ_ONCE_TASK_STACK(task, frame->fp);
+			pc = READ_ONCE_TASK_STACK(task, frame->ra);
+			pc = ftrace_graph_ret_addr(current, &graph_idx, pc,
 						   &frame->ra);
 			if (pc >= (unsigned long)handle_exception &&
 			    pc < (unsigned long)&ret_from_exception_end) {