alistair23-linux/arch/arm64/kernel/stacktrace.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 * Stack tracing support
 *
 * Copyright (C) 2012 ARM Ltd.
 */
#include <linux/kernel.h>
#include <linux/export.h>
#include <linux/ftrace.h>
#include <linux/kprobes.h>
#include <linux/sched.h>
#include <linux/sched/debug.h>
#include <linux/sched/task_stack.h>
#include <linux/stacktrace.h>

#include <asm/irq.h>
#include <asm/stack_pointer.h>
#include <asm/stacktrace.h>

/*
 * AArch64 PCS assigns the frame pointer to x29.
 *
 * A simple function prologue looks like this:
 * 	sub	sp, sp, #0x10
 *   	stp	x29, x30, [sp]
 *	mov	x29, sp
 *
 * A simple function epilogue looks like this:
 *	mov	sp, x29
 *	ldp	x29, x30, [sp]
 *	add	sp, sp, #0x10
 */

/*
 * Unwind from one frame record (A) to the next frame record (B).
 *
 * We terminate early if the location of B indicates a malformed chain of frame
 * records (e.g. a cycle), determined based on the location and fp value of A
 * and the location (but not the fp value) of B.
 */
int notrace unwind_frame(struct task_struct *tsk, struct stackframe *frame)
{
	unsigned long fp = frame->fp;
	struct stack_info info;

	if (fp & 0xf)
		return -EINVAL;

	if (!tsk)
		tsk = current;

	if (!on_accessible_stack(tsk, fp, &info))
		return -EINVAL;

	if (test_bit(info.type, frame->stacks_done))
		return -EINVAL;

	/*
	 * As stacks grow downward, any valid record on the same stack must be
	 * at a strictly higher address than the prior record.
	 *
	 * Stacks can nest in several valid orders, e.g.
	 *
	 * TASK -> IRQ -> OVERFLOW -> SDEI_NORMAL
	 * TASK -> SDEI_NORMAL -> SDEI_CRITICAL -> OVERFLOW
	 *
	 * ... but the nesting itself is strict. Once we transition from one
	 * stack to another, it's never valid to unwind back to that first
	 * stack.
	 */
	if (info.type == frame->prev_type) {
		if (fp <= frame->prev_fp)
			return -EINVAL;
	} else {
		set_bit(frame->prev_type, frame->stacks_done);
	}

	/*
	 * Record this frame record's values and location. The prev_fp and
	 * prev_type are only meaningful to the next unwind_frame() invocation.
	 */
	frame->fp = READ_ONCE_NOCHECK(*(unsigned long *)(fp));
	frame->pc = READ_ONCE_NOCHECK(*(unsigned long *)(fp + 8));
	frame->prev_fp = fp;
	frame->prev_type = info.type;

#ifdef CONFIG_FUNCTION_GRAPH_TRACER
	if (tsk->ret_stack &&
			(frame->pc == (unsigned long)return_to_handler)) {
		struct ftrace_ret_stack *ret_stack;
		/*
		 * This is a case where function graph tracer has
		 * modified a return address (LR) in a stack frame
		 * to hook a function return.
		 * So replace it to an original value.
		 */
		ret_stack = ftrace_graph_get_ret_stack(tsk, frame->graph++);
		if (WARN_ON_ONCE(!ret_stack))
			return -EINVAL;
		frame->pc = ret_stack->ret;
	}
#endif /* CONFIG_FUNCTION_GRAPH_TRACER */

	/*
	 * Frames created upon entry from EL0 have NULL FP and PC values, so
	 * don't bother reporting these. Frames created by __noreturn functions
	 * might have a valid FP even if PC is bogus, so only terminate where
	 * both are NULL.
	 */
	if (!frame->fp && !frame->pc)
		return -EINVAL;

	return 0;
}
NOKPROBE_SYMBOL(unwind_frame);

void notrace walk_stackframe(struct task_struct *tsk, struct stackframe *frame,
		     int (*fn)(struct stackframe *, void *), void *data)
{
	while (1) {
		int ret;

		if (fn(frame, data))
			break;
		ret = unwind_frame(tsk, frame);
		if (ret < 0)
			break;
	}
}
NOKPROBE_SYMBOL(walk_stackframe);

#ifdef CONFIG_STACKTRACE
struct stack_trace_data {
	struct stack_trace *trace;
	unsigned int no_sched_functions;
	unsigned int skip;
};

static int save_trace(struct stackframe *frame, void *d)
{
	struct stack_trace_data *data = d;
	struct stack_trace *trace = data->trace;
	unsigned long addr = frame->pc;

	if (data->no_sched_functions && in_sched_functions(addr))
		return 0;
	if (data->skip) {
		data->skip--;
		return 0;
	}

	trace->entries[trace->nr_entries++] = addr;

	return trace->nr_entries >= trace->max_entries;
}

void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
{
	struct stack_trace_data data;
	struct stackframe frame;

	data.trace = trace;
	data.skip = trace->skip;
	data.no_sched_functions = 0;

	start_backtrace(&frame, regs->regs[29], regs->pc);
	walk_stackframe(current, &frame, save_trace, &data);
}
EXPORT_SYMBOL_GPL(save_stack_trace_regs);

static noinline void __save_stack_trace(struct task_struct *tsk,
	struct stack_trace *trace, unsigned int nosched)
{
	struct stack_trace_data data;
	struct stackframe frame;

	if (!try_get_task_stack(tsk))
		return;

	data.trace = trace;
	data.skip = trace->skip;
	data.no_sched_functions = nosched;

	if (tsk != current) {
		start_backtrace(&frame, thread_saved_fp(tsk),
				thread_saved_pc(tsk));
	} else {
		/* We don't want this function nor the caller */
		data.skip += 2;
		start_backtrace(&frame,
				(unsigned long)__builtin_frame_address(0),
				(unsigned long)__save_stack_trace);
	}

	walk_stackframe(tsk, &frame, save_trace, &data);

	put_task_stack(tsk);
}
EXPORT_SYMBOL_GPL(save_stack_trace_tsk);

void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
{
	__save_stack_trace(tsk, trace, 1);
}

void save_stack_trace(struct stack_trace *trace)
{
	__save_stack_trace(current, trace, 0);
}

EXPORT_SYMBOL_GPL(save_stack_trace);
#endif