Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
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>
 <36d3c98e-24bb-988c-57a3-82730cc75cbc@huawei.com>
 <CACOAw_wVEw3+Kyz2HvvanhhP2_-xQy9wjfpDt5G0ahXM8o-V-Q@mail.gmail.com>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <3eade7bf-ce66-e502-24e7-e3a1e548dd77@huawei.com>
Date:   Mon, 8 Jun 2020 15:43:46 +0800
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: <CACOAw_wVEw3+Kyz2HvvanhhP2_-xQy9wjfpDt5G0ahXM8o-V-Q@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 2020/6/8 15:19, Daeho Jeong wrote:
> Yes, I agree with you about each vendor has different implementation on discard.
> So, we might be gonna use the combination of zeroing and send discards
> for a more
> secure solution. :)

IIRC, current solution is:

- pin file
- get all block addresses of file
- write zero to block addresses
- issue discard

Is that correct?

Could we handle those logic (zero out & discard) in new interface
(may be named as {F2FS,EXT4}_IOC_SEC_TRIM_FILE)? then userspace logic
could be quite simple later, and also memcpy could be avoid to make
destruction process more efficient.

Just raw proposal. :)

Thanks,

> I think we still need a discard interface to unmap from the mapping
> table of the storage device side.
> 
> Thanks,
> 
> 2020년 6월 8일 (월) 오후 3:57, Chao Yu <yuchao0@huawei.com>님이 작성:
>>
>> 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;
>>>>>
>>> .
>>>
> .
>