/* SPDX-License-Identifier: GPL-2.0 */

#include <linux/export.h>
#include <linux/sched.h>
#include <linux/sched/task.h>
#include <linux/sched/task_stack.h>
#include <linux/interrupt.h>
#include <asm/sections.h>
#include <asm/ptrace.h>
#include <asm/bitops.h>
#include <asm/stacktrace.h>
#include <asm/unwind.h>

unsigned long unwind_get_return_address(struct unwind_state *state)
{
        if (unwind_done(state))
                return 0;
        return __kernel_text_address(state->ip) ? state->ip : 0;
}
EXPORT_SYMBOL_GPL(unwind_get_return_address);

static bool outside_of_stack(struct unwind_state *state, unsigned long sp)
{
        return (sp <= state->sp) ||
                (sp > state->stack_info.end - sizeof(struct stack_frame));
}

static bool update_stack_info(struct unwind_state *state, unsigned long sp)
{
        struct stack_info *info = &state->stack_info;
        unsigned long *mask = &state->stack_mask;

        /* New stack pointer leaves the current stack */
        if (get_stack_info(sp, state->task, info, mask) != 0 ||
            !on_stack(info, sp, sizeof(struct stack_frame)))
                /* 'sp' does not point to a valid stack */
                return false;
        return true;
}

static inline bool is_final_pt_regs(struct unwind_state *state,
                                    struct pt_regs *regs)
{
        /* user mode or kernel thread pt_regs at the bottom of task stack */
        if (task_pt_regs(state->task) == regs)
                return true;

        /* user mode pt_regs at the bottom of irq stack */
        return state->stack_info.type == STACK_TYPE_IRQ &&
               state->stack_info.end - sizeof(struct pt_regs) == (unsigned long)regs &&
               READ_ONCE_NOCHECK(regs->psw.mask) & PSW_MASK_PSTATE;
}

/* Avoid KMSAN false positives from touching uninitialized frames. */
__no_kmsan_checks
bool unwind_next_frame(struct unwind_state *state)
{
        struct stack_info *info = &state->stack_info;
        struct stack_frame *sf;
        struct pt_regs *regs;
        unsigned long sp, ip;
        bool reliable;

        regs = state->regs;
        if (unlikely(regs)) {
                sp = state->sp;
                sf = (struct stack_frame *) sp;
                ip = READ_ONCE_NOCHECK(sf->gprs[8]);
                reliable = false;
                regs = NULL;
                /* skip bogus %r14 or if is the same as regs->psw.addr */
                if (!__kernel_text_address(ip) || state->ip == unwind_recover_ret_addr(state, ip)) {
                        state->regs = NULL;
                        return unwind_next_frame(state);
                }
        } else {
                sf = (struct stack_frame *) state->sp;
                sp = READ_ONCE_NOCHECK(sf->back_chain);
                if (likely(sp)) {
                        /* Non-zero back-chain points to the previous frame */
                        if (unlikely(outside_of_stack(state, sp))) {
                                if (!update_stack_info(state, sp))
                                        goto out_err;
                        }
                        sf = (struct stack_frame *) sp;
                        ip = READ_ONCE_NOCHECK(sf->gprs[8]);
                        reliable = true;
                } else {
                        /* No back-chain, look for a pt_regs structure */
                        sp = state->sp + STACK_FRAME_OVERHEAD;
                        if (!on_stack(info, sp, sizeof(struct pt_regs)))
                                goto out_err;
                        regs = (struct pt_regs *) sp;
                        if (is_final_pt_regs(state, regs))
                                goto out_stop;
                        ip = READ_ONCE_NOCHECK(regs->psw.addr);
                        sp = READ_ONCE_NOCHECK(regs->gprs[15]);
                        if (unlikely(outside_of_stack(state, sp))) {
                                if (!update_stack_info(state, sp))
                                        goto out_err;
                        }
                        reliable = true;
                }
        }

        /* Sanity check: ABI requires SP to be aligned 8 bytes. */
        if (sp & 0x7)
                goto out_err;

        /* Update unwind state */
        state->sp = sp;
        state->regs = regs;
        state->reliable = reliable;
        state->ip = unwind_recover_ret_addr(state, ip);
        return true;

out_err:
        state->error = true;
out_stop:
        state->stack_info.type = STACK_TYPE_UNKNOWN;
        return false;
}
EXPORT_SYMBOL_GPL(unwind_next_frame);

/* Avoid KMSAN false positives from touching uninitialized frames. */
__no_kmsan_checks
void __unwind_start(struct unwind_state *state, struct task_struct *task,
                    struct pt_regs *regs, unsigned long first_frame)
{
        struct stack_info *info = &state->stack_info;
        struct stack_frame *sf;
        unsigned long ip, sp;

        memset(state, 0, sizeof(*state));
        state->task = task;
        state->regs = regs;

        /* Don't even attempt to start from user mode regs: */
        if (regs && user_mode(regs)) {
                info->type = STACK_TYPE_UNKNOWN;
                return;
        }

        /* Get the instruction pointer from pt_regs or the stack frame */
        if (regs) {
                ip = regs->psw.addr;
                sp = regs->gprs[15];
        } else if (task == current) {
                sp = current_frame_address();
        } else {
                sp = task->thread.ksp;
        }

        /* Get current stack pointer and initialize stack info */
        if (!update_stack_info(state, sp)) {
                /* Something is wrong with the stack pointer */
                info->type = STACK_TYPE_UNKNOWN;
                state->error = true;
                return;
        }

        if (!regs) {
                /* Stack frame is within valid stack */
                sf = (struct stack_frame *)sp;
                ip = READ_ONCE_NOCHECK(sf->gprs[8]);
        }

        /* Update unwind state */
        state->sp = sp;
        state->reliable = true;
        state->ip = unwind_recover_ret_addr(state, ip);

        if (!first_frame)
                return;
        /* Skip through the call chain to the specified starting frame */
        while (!unwind_done(state)) {
                if (on_stack(&state->stack_info, first_frame, sizeof(struct stack_frame))) {
                        if (state->sp >= first_frame)
                                break;
                }
                unwind_next_frame(state);
        }
}
EXPORT_SYMBOL_GPL(__unwind_start);