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Subject: Re: [f2fs-dev] [PATCH] f2fs: add F2FS_IOC_TRIM_FILE ioctl
To:     Daeho Jeong <daeho43@gmail.com>
CC:     <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>,
        <kernel-team@android.com>, Daeho Jeong <daehojeong@google.com>
References: <20200605042746.201180-1-daeho43@gmail.com>
 <fd9bd76c-1864-2cfc-bf86-ef705c8a407d@huawei.com>
 <CACOAw_yw+zczoWpNvYz_UHRYjr8BS+xKK=7_BKi0_0wEhp8Lvg@mail.gmail.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <36d3c98e-24bb-988c-57a3-82730cc75cbc@huawei.com>
Date:   Mon, 8 Jun 2020 14:57:02 +0800
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On 2020/6/8 11:36, Daeho Jeong wrote:
> Yes, this is for security key destruction.
> 
> AFAIK, discard will unmap the data block and, after done it,
> we can read either zero data or garbage data from that block depending
> on eMMC/UFS.

Since spec didn't restrict how vendor implement the erase interface, so
in order to enhance performance of discard interface, vendor could implement
it as an async one, which may not zero mapping entry(L1 table), instead, it
could set related bitmap to invalid that mapping entry, than later if device
allow user to access that invalid mapping entry, key info may be explosed,

It's completely up to how vendor implement the interface, so I think there is
still risk to use discard.

Thanks,

> In a view point of read data, it might be the same with zeroing the data block.
> However, since we can even unmap that block, I believe discard is
> safer than zeroing out.
> 
> 2020년 6월 8일 (월) 오전 11:46, Chao Yu <yuchao0@huawei.com>님이 작성:
>>
>> On 2020/6/5 12:27, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@google.com>
>>>
>>> Added a new ioctl to send discard commands to whole data area of
>>> a regular file for security reason.
>>
>> I guess this interface is introduced for security key destruction, if I'm
>> right, however, IIRC, discard(erase) semantics in eMMC/UFS spec won't
>> guarantee that data which was discard could be zeroed out, so after discard,
>> the key still have risk of exposure. So instead, should we use sb_issue_zeroout()?
>>
>> Thanks,
>>
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@google.com>
>>> ---
>>>  fs/f2fs/f2fs.h |   1 +
>>>  fs/f2fs/file.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++++
>>>  2 files changed, 130 insertions(+)
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index c812fb8e2d9c..9ae81d0fefa0 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -434,6 +434,7 @@ static inline bool __has_cursum_space(struct f2fs_journal *journal,
>>>                                       _IOR(F2FS_IOCTL_MAGIC, 18, __u64)
>>>  #define F2FS_IOC_RESERVE_COMPRESS_BLOCKS                             \
>>>                                       _IOR(F2FS_IOCTL_MAGIC, 19, __u64)
>>> +#define F2FS_IOC_TRIM_FILE           _IO(F2FS_IOCTL_MAGIC, 20)
>>>
>>>  #define F2FS_IOC_GET_VOLUME_NAME     FS_IOC_GETFSLABEL
>>>  #define F2FS_IOC_SET_VOLUME_NAME     FS_IOC_SETFSLABEL
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index dfa1ac2d751a..58507bb5649c 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -3749,6 +3749,132 @@ static int f2fs_reserve_compress_blocks(struct file *filp, unsigned long arg)
>>>       return ret;
>>>  }
>>>
>>> +static int f2fs_trim_file(struct file *filp)
>>> +{
>>> +     struct inode *inode = file_inode(filp);
>>> +     struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>> +     struct address_space *mapping = inode->i_mapping;
>>> +     struct bio *bio = NULL;
>>> +     struct block_device *prev_bdev = NULL;
>>> +     loff_t file_size;
>>> +     pgoff_t index, pg_start = 0, pg_end;
>>> +     block_t prev_block = 0, len = 0;
>>> +     int ret = 0;
>>> +
>>> +     if (!f2fs_hw_support_discard(sbi))
>>> +             return -EOPNOTSUPP;
>>> +
>>> +     if (!S_ISREG(inode->i_mode) || f2fs_is_atomic_file(inode) ||
>>> +                     f2fs_compressed_file(inode))
>>> +             return -EINVAL;
>>> +
>>> +     if (f2fs_readonly(sbi->sb))
>>> +             return -EROFS;
>>> +
>>> +     ret = mnt_want_write_file(filp);
>>> +     if (ret)
>>> +             return ret;
>>> +
>>> +     inode_lock(inode);
>>> +
>>> +     file_size = i_size_read(inode);
>>> +     if (!file_size)
>>> +             goto err;
>>> +     pg_end = (pgoff_t)round_up(file_size, PAGE_SIZE) >> PAGE_SHIFT;
>>> +
>>> +     ret = f2fs_convert_inline_inode(inode);
>>> +     if (ret)
>>> +             goto err;
>>> +
>>> +     down_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> +     down_write(&F2FS_I(inode)->i_mmap_sem);
>>> +
>>> +     ret = filemap_write_and_wait(mapping);
>>> +     if (ret)
>>> +             goto out;
>>> +
>>> +     truncate_inode_pages(mapping, 0);
>>> +
>>> +     for (index = pg_start; index < pg_end;) {
>>> +             struct dnode_of_data dn;
>>> +             unsigned int end_offset;
>>> +
>>> +             set_new_dnode(&dn, inode, NULL, NULL, 0);
>>> +             ret = f2fs_get_dnode_of_data(&dn, index, LOOKUP_NODE);
>>> +             if (ret)
>>> +                     goto out;
>>> +
>>> +             end_offset = ADDRS_PER_PAGE(dn.node_page, inode);
>>> +             if (pg_end < end_offset + index)
>>> +                     end_offset = pg_end - index;
>>> +
>>> +             for (; dn.ofs_in_node < end_offset;
>>> +                             dn.ofs_in_node++, index++) {
>>> +                     struct block_device *cur_bdev;
>>> +                     block_t blkaddr = f2fs_data_blkaddr(&dn);
>>> +
>>> +                     if (__is_valid_data_blkaddr(blkaddr)) {
>>> +                             if (!f2fs_is_valid_blkaddr(F2FS_I_SB(inode),
>>> +                                     blkaddr, DATA_GENERIC_ENHANCE)) {
>>> +                                     ret = -EFSCORRUPTED;
>>> +                                     goto out;
>>> +                             }
>>> +                     } else
>>> +                             continue;
>>> +
>>> +                     cur_bdev = f2fs_target_device(sbi, blkaddr, NULL);
>>> +                     if (f2fs_is_multi_device(sbi)) {
>>> +                             int i = f2fs_target_device_index(sbi, blkaddr);
>>> +
>>> +                             blkaddr -= FDEV(i).start_blk;
>>> +                     }
>>> +
>>> +                     if (len) {
>>> +                             if (prev_bdev == cur_bdev &&
>>> +                                     blkaddr == prev_block + len) {
>>> +                                     len++;
>>> +                             } else {
>>> +                                     ret = __blkdev_issue_discard(prev_bdev,
>>> +                                             SECTOR_FROM_BLOCK(prev_block),
>>> +                                             SECTOR_FROM_BLOCK(len),
>>> +                                             GFP_NOFS, 0, &bio);
>>> +                                     if (ret)
>>> +                                             goto out;
>>> +> +                                  len = 0;
>>> +                             }
>>> +                     }
>>> +
>>> +                     if (!len) {
>>> +                             prev_bdev = cur_bdev;
>>> +                             prev_block = blkaddr;
>>> +                             len = 1;
>>> +                     }
>>> +             }
>>> +
>>> +             f2fs_put_dnode(&dn);
>>> +     }
>>> +
>>> +     if (len)
>>> +             ret = __blkdev_issue_discard(prev_bdev,
>>> +                                     SECTOR_FROM_BLOCK(prev_block),
>>> +                                     SECTOR_FROM_BLOCK(len),
>>> +                                     GFP_NOFS, 0, &bio);
>>> +out:
>>> +     if (bio) {
>>> +             ret = submit_bio_wait(bio);
>>> +             bio_put(bio);
>>> +     }
>>> +
>>> +     up_write(&F2FS_I(inode)->i_mmap_sem);
>>> +     up_write(&F2FS_I(inode)->i_gc_rwsem[WRITE]);
>>> +err:
>>> +     inode_unlock(inode);
>>> +     mnt_drop_write_file(filp);
>>> +
>>> +     return ret;
>>> +}
>>> +
>>>  long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>>  {
>>>       if (unlikely(f2fs_cp_error(F2FS_I_SB(file_inode(filp)))))
>>> @@ -3835,6 +3961,8 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>>               return f2fs_release_compress_blocks(filp, arg);
>>>       case F2FS_IOC_RESERVE_COMPRESS_BLOCKS:
>>>               return f2fs_reserve_compress_blocks(filp, arg);
>>> +     case F2FS_IOC_TRIM_FILE:
>>> +             return f2fs_trim_file(filp);
>>>       default:
>>>               return -ENOTTY;
>>>       }
>>> @@ -4004,6 +4132,7 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>>>       case F2FS_IOC_GET_COMPRESS_BLOCKS:
>>>       case F2FS_IOC_RELEASE_COMPRESS_BLOCKS:
>>>       case F2FS_IOC_RESERVE_COMPRESS_BLOCKS:
>>> +     case F2FS_IOC_TRIM_FILE:
>>>               break;
>>>       default:
>>>               return -ENOIOCTLCMD;
>>>
> .
>