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In-Reply-To: <36d3c98e-24bb-988c-57a3-82730cc75cbc@huawei.com>
From:   Daeho Jeong <daeho43@gmail.com>
Date:   Mon, 8 Jun 2020 16:19:43 +0900
Message-ID: <CACOAw_wVEw3+Kyz2HvvanhhP2_-xQy9wjfpDt5G0ahXM8o-V-Q@mail.gmail.com>
Subject: Re: [f2fs-dev] [PATCH] f2fs: add F2FS_IOC_TRIM_FILE ioctl
To:     Chao Yu <yuchao0@huawei.com>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com,
        Daeho Jeong <daehojeong@google.com>
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Yes, I agree with you about each vendor has different implementation on dis=
card.
So, we might be gonna use the combination of zeroing and send discards
for a more
secure solution. :)
I think we still need a discard interface to unmap from the mapping
table of the storage device side.

Thanks,

2020=EB=85=84 6=EC=9B=94 8=EC=9D=BC (=EC=9B=94) =EC=98=A4=ED=9B=84 3:57, Ch=
ao Yu <yuchao0@huawei.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
>
> 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 implem=
ent
> 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 dev=
ice
> 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 ther=
e is
> still risk to use discard.
>
> Thanks,
>
> > In a view point of read data, it might be the same with zeroing the dat=
a block.
> > However, since we can even unmap that block, I believe discard is
> > safer than zeroing out.
> >
> > 2020=EB=85=84 6=EC=9B=94 8=EC=9D=BC (=EC=9B=94) =EC=98=A4=EC=A0=84 11:4=
6, Chao Yu <yuchao0@huawei.com>=EB=8B=98=EC=9D=B4 =EC=9E=91=EC=84=B1:
> >>
> >> 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 di=
scard,
> >> the key still have risk of exposure. So instead, should we use sb_issu=
e_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, __u6=
4)
> >>>  #define F2FS_IOC_RESERVE_COMPRESS_BLOCKS                            =
 \
> >>>                                       _IOR(F2FS_IOCTL_MAGIC, 19, __u6=
4)
> >>> +#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(struc=
t file *filp, unsigned long arg)
> >>>       return ret;
> >>>  }
> >>>
> >>> +static int f2fs_trim_file(struct file *filp)
> >>> +{
> >>> +     struct inode *inode =3D file_inode(filp);
> >>> +     struct f2fs_sb_info *sbi =3D F2FS_I_SB(inode);
> >>> +     struct address_space *mapping =3D inode->i_mapping;
> >>> +     struct bio *bio =3D NULL;
> >>> +     struct block_device *prev_bdev =3D NULL;
> >>> +     loff_t file_size;
> >>> +     pgoff_t index, pg_start =3D 0, pg_end;
> >>> +     block_t prev_block =3D 0, len =3D 0;
> >>> +     int ret =3D 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 =3D mnt_want_write_file(filp);
> >>> +     if (ret)
> >>> +             return ret;
> >>> +
> >>> +     inode_lock(inode);
> >>> +
> >>> +     file_size =3D i_size_read(inode);
> >>> +     if (!file_size)
> >>> +             goto err;
> >>> +     pg_end =3D (pgoff_t)round_up(file_size, PAGE_SIZE) >> PAGE_SHIF=
T;
> >>> +
> >>> +     ret =3D 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 =3D filemap_write_and_wait(mapping);
> >>> +     if (ret)
> >>> +             goto out;
> >>> +
> >>> +     truncate_inode_pages(mapping, 0);
> >>> +
> >>> +     for (index =3D pg_start; index < pg_end;) {
> >>> +             struct dnode_of_data dn;
> >>> +             unsigned int end_offset;
> >>> +
> >>> +             set_new_dnode(&dn, inode, NULL, NULL, 0);
> >>> +             ret =3D f2fs_get_dnode_of_data(&dn, index, LOOKUP_NODE)=
;
> >>> +             if (ret)
> >>> +                     goto out;
> >>> +
> >>> +             end_offset =3D ADDRS_PER_PAGE(dn.node_page, inode);
> >>> +             if (pg_end < end_offset + index)
> >>> +                     end_offset =3D pg_end - index;
> >>> +
> >>> +             for (; dn.ofs_in_node < end_offset;
> >>> +                             dn.ofs_in_node++, index++) {
> >>> +                     struct block_device *cur_bdev;
> >>> +                     block_t blkaddr =3D f2fs_data_blkaddr(&dn);
> >>> +
> >>> +                     if (__is_valid_data_blkaddr(blkaddr)) {
> >>> +                             if (!f2fs_is_valid_blkaddr(F2FS_I_SB(in=
ode),
> >>> +                                     blkaddr, DATA_GENERIC_ENHANCE))=
 {
> >>> +                                     ret =3D -EFSCORRUPTED;
> >>> +                                     goto out;
> >>> +                             }
> >>> +                     } else
> >>> +                             continue;
> >>> +
> >>> +                     cur_bdev =3D f2fs_target_device(sbi, blkaddr, N=
ULL);
> >>> +                     if (f2fs_is_multi_device(sbi)) {
> >>> +                             int i =3D f2fs_target_device_index(sbi,=
 blkaddr);
> >>> +
> >>> +                             blkaddr -=3D FDEV(i).start_blk;
> >>> +                     }
> >>> +
> >>> +                     if (len) {
> >>> +                             if (prev_bdev =3D=3D cur_bdev &&
> >>> +                                     blkaddr =3D=3D prev_block + len=
) {
> >>> +                                     len++;
> >>> +                             } else {
> >>> +                                     ret =3D __blkdev_issue_discard(=
prev_bdev,
> >>> +                                             SECTOR_FROM_BLOCK(prev_=
block),
> >>> +                                             SECTOR_FROM_BLOCK(len),
> >>> +                                             GFP_NOFS, 0, &bio);
> >>> +                                     if (ret)
> >>> +                                             goto out;
> >>> +> +                                  len =3D 0;
> >>> +                             }
> >>> +                     }
> >>> +
> >>> +                     if (!len) {
> >>> +                             prev_bdev =3D cur_bdev;
> >>> +                             prev_block =3D blkaddr;
> >>> +                             len =3D 1;
> >>> +                     }
> >>> +             }
> >>> +
> >>> +             f2fs_put_dnode(&dn);
> >>> +     }
> >>> +
> >>> +     if (len)
> >>> +             ret =3D __blkdev_issue_discard(prev_bdev,
> >>> +                                     SECTOR_FROM_BLOCK(prev_block),
> >>> +                                     SECTOR_FROM_BLOCK(len),
> >>> +                                     GFP_NOFS, 0, &bio);
> >>> +out:
> >>> +     if (bio) {
> >>> +             ret =3D 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 a=
rg)
> >>>  {
> >>>       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, unsig=
ned 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;
> >>>
> > .
> >