// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright IBM Corporation, 2021
 *
 * Author: Mike Rapoport <rppt@linux.ibm.com>
 */

#include <linux/mm.h>
#include <linux/fs.h>
#include <linux/swap.h>
#include <linux/mount.h>
#include <linux/memfd.h>
#include <linux/bitops.h>
#include <linux/printk.h>
#include <linux/pagemap.h>
#include <linux/syscalls.h>
#include <linux/pseudo_fs.h>
#include <linux/secretmem.h>
#include <linux/set_memory.h>
#include <linux/sched/signal.h>

#include <uapi/linux/magic.h>

#include <asm/tlbflush.h>

#include "internal.h"

#undef pr_fmt
#define pr_fmt(fmt) "secretmem: " fmt

/*
 * Define mode and flag masks to allow validation of the system call
 * parameters.
 */
#define SECRETMEM_MODE_MASK     (0x0)
#define SECRETMEM_FLAGS_MASK    SECRETMEM_MODE_MASK

static bool secretmem_enable __ro_after_init;
module_param_named(enable, secretmem_enable, bool, 0400);
MODULE_PARM_DESC(secretmem_enable,
                 "Enable secretmem and memfd_secret(2) system call");

static atomic_t secretmem_users;

bool secretmem_active(void)
{
        return !!atomic_read(&secretmem_users);
}

static vm_fault_t secretmem_fault(struct vm_fault *vmf)
{
        struct address_space *mapping = vmf->vma->vm_file->f_mapping;
        struct inode *inode = file_inode(vmf->vma->vm_file);
        pgoff_t offset = vmf->pgoff;
        gfp_t gfp = vmf->gfp_mask;
        unsigned long addr;
        struct page *page;
        int err;

        if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode))
                return vmf_error(-EINVAL);

retry:
        page = find_lock_page(mapping, offset);
        if (!page) {
                page = alloc_page(gfp | __GFP_ZERO);
                if (!page)
                        return VM_FAULT_OOM;

                err = set_direct_map_invalid_noflush(page);
                if (err) {
                        put_page(page);
                        return vmf_error(err);
                }

                __SetPageUptodate(page);
                err = add_to_page_cache_lru(page, mapping, offset, gfp);
                if (unlikely(err)) {
                        put_page(page);
                        /*
                         * If a split of large page was required, it
                         * already happened when we marked the page invalid
                         * which guarantees that this call won't fail
                         */
                        set_direct_map_default_noflush(page);
                        if (err == -EEXIST)
                                goto retry;

                        return vmf_error(err);
                }

                addr = (unsigned long)page_address(page);
                flush_tlb_kernel_range(addr, addr + PAGE_SIZE);
        }

        vmf->page = page;
        return VM_FAULT_LOCKED;
}

static const struct vm_operations_struct secretmem_vm_ops = {
        .fault = secretmem_fault,
};

static int secretmem_release(struct inode *inode, struct file *file)
{
        atomic_dec(&secretmem_users);
        return 0;
}

static int secretmem_mmap(struct file *file, struct vm_area_struct *vma)
{
        unsigned long len = vma->vm_end - vma->vm_start;

        if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
                return -EINVAL;

        if (mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
                return -EAGAIN;

        vma->vm_flags |= VM_LOCKED | VM_DONTDUMP;
        vma->vm_ops = &secretmem_vm_ops;

        return 0;
}

bool vma_is_secretmem(struct vm_area_struct *vma)
{
        return vma->vm_ops == &secretmem_vm_ops;
}

static const struct file_operations secretmem_fops = {
        .release        = secretmem_release,
        .mmap           = secretmem_mmap,
};

static bool secretmem_isolate_page(struct page *page, isolate_mode_t mode)
{
        return false;
}

static int secretmem_migratepage(struct address_space *mapping,
                                 struct page *newpage, struct page *page,
                                 enum migrate_mode mode)
{
        return -EBUSY;
}

static void secretmem_freepage(struct page *page)
{
        set_direct_map_default_noflush(page);
        clear_highpage(page);
}

const struct address_space_operations secretmem_aops = {
        .set_page_dirty = __set_page_dirty_no_writeback,
        .freepage       = secretmem_freepage,
        .migratepage    = secretmem_migratepage,
        .isolate_page   = secretmem_isolate_page,
};

static struct vfsmount *secretmem_mnt;

static struct file *secretmem_file_create(unsigned long flags)
{
        struct file *file = ERR_PTR(-ENOMEM);
        struct inode *inode;

        inode = alloc_anon_inode(secretmem_mnt->mnt_sb);
        if (IS_ERR(inode))
                return ERR_CAST(inode);

        file = alloc_file_pseudo(inode, secretmem_mnt, "secretmem",
                                 O_RDWR, &secretmem_fops);
        if (IS_ERR(file))
                goto err_free_inode;

        mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER);
        mapping_set_unevictable(inode->i_mapping);

        inode->i_mapping->a_ops = &secretmem_aops;

        /* pretend we are a normal file with zero size */
        inode->i_mode |= S_IFREG;
        inode->i_size = 0;

        return file;

err_free_inode:
        iput(inode);
        return file;
}

SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)
{
        struct file *file;
        int fd, err;

        /* make sure local flags do not confict with global fcntl.h */
        BUILD_BUG_ON(SECRETMEM_FLAGS_MASK & O_CLOEXEC);

        if (!secretmem_enable)
                return -ENOSYS;

        if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))
                return -EINVAL;
        if (atomic_read(&secretmem_users) < 0)
                return -ENFILE;

        fd = get_unused_fd_flags(flags & O_CLOEXEC);
        if (fd < 0)
                return fd;

        file = secretmem_file_create(flags);
        if (IS_ERR(file)) {
                err = PTR_ERR(file);
                goto err_put_fd;
        }

        file->f_flags |= O_LARGEFILE;

        atomic_inc(&secretmem_users);
        fd_install(fd, file);
        return fd;

err_put_fd:
        put_unused_fd(fd);
        return err;
}

static int secretmem_init_fs_context(struct fs_context *fc)
{
        return init_pseudo(fc, SECRETMEM_MAGIC) ? 0 : -ENOMEM;
}

static struct file_system_type secretmem_fs = {
        .name           = "secretmem",
        .init_fs_context = secretmem_init_fs_context,
        .kill_sb        = kill_anon_super,
};

static int secretmem_init(void)
{
        int ret = 0;

        if (!secretmem_enable)
                return ret;

        secretmem_mnt = kern_mount(&secretmem_fs);
        if (IS_ERR(secretmem_mnt))
                ret = PTR_ERR(secretmem_mnt);

        /* prevent secretmem mappings from ever getting PROT_EXEC */
        secretmem_mnt->mnt_flags |= MNT_NOEXEC;

        return ret;
}
fs_initcall(secretmem_init);