// 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