// 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/pointer_auth.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 &&
                (ptrauth_strip_insn_pac(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 */

        frame->pc = ptrauth_strip_insn_pac(frame->pc);

        /*
         * 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,
                             bool (*fn)(void *, unsigned long), void *data)
{
        while (1) {
                int ret;

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

static void dump_backtrace_entry(unsigned long where, const char *loglvl)
{
        printk("%s %pS\n", loglvl, (void *)where);
}

void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk,
                    const char *loglvl)
{
        struct stackframe frame;
        int skip = 0;

        pr_debug("%s(regs = %p tsk = %p)\n", __func__, regs, tsk);

        if (regs) {
                if (user_mode(regs))
                        return;
                skip = 1;
        }

        if (!tsk)
                tsk = current;

        if (!try_get_task_stack(tsk))
                return;

        if (tsk == current) {
                start_backtrace(&frame,
                                (unsigned long)__builtin_frame_address(0),
                                (unsigned long)dump_backtrace);
        } else {
                /*
                 * task blocked in __switch_to
                 */
                start_backtrace(&frame,
                                thread_saved_fp(tsk),
                                thread_saved_pc(tsk));
        }

        printk("%sCall trace:\n", loglvl);
        do {
                /* skip until specified stack frame */
                if (!skip) {
                        dump_backtrace_entry(frame.pc, loglvl);
                } else if (frame.fp == regs->regs[29]) {
                        skip = 0;
                        /*
                         * Mostly, this is the case where this function is
                         * called in panic/abort. As exception handler's
                         * stack frame does not contain the corresponding pc
                         * at which an exception has taken place, use regs->pc
                         * instead.
                         */
                        dump_backtrace_entry(regs->pc, loglvl);
                }
        } while (!unwind_frame(tsk, &frame));

        put_task_stack(tsk);
}

void show_stack(struct task_struct *tsk, unsigned long *sp, const char *loglvl)
{
        dump_backtrace(NULL, tsk, loglvl);
        barrier();
}

#ifdef CONFIG_STACKTRACE

void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
                     struct task_struct *task, struct pt_regs *regs)
{
        struct stackframe frame;

        if (regs)
                start_backtrace(&frame, regs->regs[29], regs->pc);
        else if (task == current)
                start_backtrace(&frame,
                                (unsigned long)__builtin_frame_address(0),
                                (unsigned long)arch_stack_walk);
        else
                start_backtrace(&frame, thread_saved_fp(task),
                                thread_saved_pc(task));

        walk_stackframe(task, &frame, consume_entry, cookie);
}

#endif