// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2015 Thomas Meyer (thomas@m3y3r.de)
 * Copyright (C) 2002 - 2007 Jeff Dike (jdike@{addtoit,linux.intel}.com)
 */

#include <linux/mm.h>
#include <linux/sched/signal.h>
#include <linux/slab.h>

#include <shared/irq_kern.h>
#include <asm/pgalloc.h>
#include <asm/sections.h>
#include <asm/mmu_context.h>
#include <as-layout.h>
#include <os.h>
#include <skas.h>
#include <stub-data.h>

/* Ensure the stub_data struct covers the allocated area */
static_assert(sizeof(struct stub_data) == STUB_DATA_PAGES * UM_KERN_PAGE_SIZE);

static spinlock_t mm_list_lock;
static struct list_head mm_list;

struct mutex *__get_turnstile(struct mm_id *mm_id)
{
        struct mm_context *ctx = container_of(mm_id, struct mm_context, id);

        return &ctx->turnstile;
}

void enter_turnstile(struct mm_id *mm_id)
{
        mutex_lock(__get_turnstile(mm_id));
}

void exit_turnstile(struct mm_id *mm_id)
{
        mutex_unlock(__get_turnstile(mm_id));
}

int init_new_context(struct task_struct *task, struct mm_struct *mm)
{
        struct mm_id *new_id = &mm->context.id;
        unsigned long stack = 0;
        int ret = -ENOMEM;

        mutex_init(&mm->context.turnstile);
        spin_lock_init(&mm->context.sync_tlb_lock);

        stack = __get_free_pages(GFP_KERNEL | __GFP_ZERO, ilog2(STUB_DATA_PAGES));
        if (stack == 0)
                goto out;

        new_id->stack = stack;
        new_id->syscall_data_len = 0;
        new_id->syscall_fd_num = 0;

        scoped_guard(spinlock_irqsave, &mm_list_lock) {
                /* Insert into list, used for lookups when the child dies */
                list_add(&mm->context.list, &mm_list);
        }

        ret = start_userspace(new_id);
        if (ret < 0)
                goto out_free;

        /* Ensure the new MM is clean and nothing unwanted is mapped */
        unmap(new_id, 0, STUB_START);

        return 0;

 out_free:
        free_pages(new_id->stack, ilog2(STUB_DATA_PAGES));
 out:
        return ret;
}

void destroy_context(struct mm_struct *mm)
{
        struct mm_context *mmu = &mm->context;

        /*
         * If init_new_context wasn't called, this will be
         * zero, resulting in a kill(0), which will result in the
         * whole UML suddenly dying.  Also, cover negative and
         * 1 cases, since they shouldn't happen either.
         *
         * Negative cases happen if the child died unexpectedly.
         */
        if (mmu->id.pid >= 0 && mmu->id.pid < 2) {
                printk(KERN_ERR "corrupt mm_context - pid = %d\n",
                       mmu->id.pid);
                return;
        }

        scoped_guard(spinlock_irqsave, &mm_list_lock)
                list_del(&mm->context.list);

        if (mmu->id.pid > 0) {
                os_kill_ptraced_process(mmu->id.pid, 1);
                mmu->id.pid = -1;
        }

        if (using_seccomp && mmu->id.sock)
                os_close_file(mmu->id.sock);

        free_pages(mmu->id.stack, ilog2(STUB_DATA_PAGES));
}

static irqreturn_t mm_sigchld_irq(int irq, void* dev)
{
        struct mm_context *mm_context;
        pid_t pid;

        guard(spinlock)(&mm_list_lock);

        while ((pid = os_reap_child()) > 0) {
                /*
                * A child died, check if we have an MM with the PID. This is
                * only relevant in SECCOMP mode (as ptrace will fail anyway).
                *
                * See wait_stub_done_seccomp for more details.
                */
                list_for_each_entry(mm_context, &mm_list, list) {
                        if (mm_context->id.pid == pid) {
                                struct stub_data *stub_data;
                                printk("Unexpectedly lost MM child! Affected tasks will segfault.");

                                /* Marks the MM as dead */
                                mm_context->id.pid = -1;

                                stub_data = (void *)mm_context->id.stack;
                                stub_data->futex = FUTEX_IN_KERN;
#if IS_ENABLED(CONFIG_SMP)
                                os_futex_wake(&stub_data->futex);
#endif

                                /*
                                 * NOTE: Currently executing syscalls by
                                 * affected tasks may finish normally.
                                 */
                                break;
                        }
                }
        }

        return IRQ_HANDLED;
}

static int __init init_child_tracking(void)
{
        int err;

        spin_lock_init(&mm_list_lock);
        INIT_LIST_HEAD(&mm_list);

        err = request_irq(SIGCHLD_IRQ, mm_sigchld_irq, 0, "SIGCHLD", NULL);
        if (err < 0)
                panic("Failed to register SIGCHLD IRQ: %d", err);

        return 0;
}
early_initcall(init_child_tracking)