From: Eric Biggers <ebiggers@kernel.org>
To: Chandan Rajendra <chandan@linux.ibm.com>
Cc: tytso@mit.edu, linux-f2fs-devel@lists.sourceforge.net,
hch@infradead.org, linux-fscrypt@vger.kernel.org,
adilger.kernel@dilger.ca, linux-fsdevel@vger.kernel.org,
jaegeuk@kernel.org, linux-ext4@vger.kernel.org
Subject: Re: [f2fs-dev] [PATCH V2 10/13] fscrypt_encrypt_page: Loop across all blocks mapped by a page range
Date: Thu, 2 May 2019 11:16:15 -0700 [thread overview]
Message-ID: <20190502181614.GA35523@gmail.com> (raw)
In-Reply-To: <11064745.d7X6JK8F7Z@dhcp-9-193-88-253>
Hi Chandan,
On Thu, May 02, 2019 at 11:22:05AM +0530, Chandan Rajendra wrote:
> On Thursday, May 2, 2019 3:59:01 AM IST Eric Biggers wrote:
> > Hi Chandan,
> >
> > On Wed, May 01, 2019 at 08:19:35PM +0530, Chandan Rajendra wrote:
> > > On Wednesday, May 1, 2019 4:38:41 AM IST Eric Biggers wrote:
> > > > On Tue, Apr 30, 2019 at 10:11:35AM -0700, Eric Biggers wrote:
> > > > > On Sun, Apr 28, 2019 at 10:01:18AM +0530, Chandan Rajendra wrote:
> > > > > > For subpage-sized blocks, this commit now encrypts all blocks mapped by
> > > > > > a page range.
> > > > > >
> > > > > > Signed-off-by: Chandan Rajendra <chandan@linux.ibm.com>
> > > > > > ---
> > > > > > fs/crypto/crypto.c | 37 +++++++++++++++++++++++++------------
> > > > > > 1 file changed, 25 insertions(+), 12 deletions(-)
> > > > > >
> > > > > > diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
> > > > > > index 4f0d832cae71..2d65b431563f 100644
> > > > > > --- a/fs/crypto/crypto.c
> > > > > > +++ b/fs/crypto/crypto.c
> > > > > > @@ -242,18 +242,26 @@ struct page *fscrypt_encrypt_page(const struct inode *inode,
> > > > >
> > > > > Need to update the function comment to clearly explain what this function
> > > > > actually does now.
> > > > >
> > > > > > {
> > > > > > struct fscrypt_ctx *ctx;
> > > > > > struct page *ciphertext_page = page;
> > > > > > + int i, page_nr_blks;
> > > > > > int err;
> > > > > >
> > > > > > BUG_ON(len % FS_CRYPTO_BLOCK_SIZE != 0);
> > > > > >
> > > > >
> > > > > Make a 'blocksize' variable so you don't have to keep calling i_blocksize().
> > > > >
> > > > > Also, you need to check whether 'len' and 'offs' are filesystem-block-aligned,
> > > > > since the code now assumes it.
> > > > >
> > > > > const unsigned int blocksize = i_blocksize(inode);
> > > > >
> > > > > if (!IS_ALIGNED(len | offs, blocksize))
> > > > > return -EINVAL;
> > > > >
> > > > > However, did you check whether that's always true for ubifs? It looks like it
> > > > > may expect to encrypt a prefix of a block, that is only padded to the next
> > > > > 16-byte boundary.
> > > > >
> > > > > > + page_nr_blks = len >> inode->i_blkbits;
> > > > > > +
> > > > > > if (inode->i_sb->s_cop->flags & FS_CFLG_OWN_PAGES) {
> > > > > > /* with inplace-encryption we just encrypt the page */
> > > > > > - err = fscrypt_do_page_crypto(inode, FS_ENCRYPT, lblk_num, page,
> > > > > > - ciphertext_page, len, offs,
> > > > > > - gfp_flags);
> > > > > > - if (err)
> > > > > > - return ERR_PTR(err);
> > > > > > -
> > > > > > + for (i = 0; i < page_nr_blks; i++) {
> > > > > > + err = fscrypt_do_page_crypto(inode, FS_ENCRYPT,
> > > > > > + lblk_num, page,
> > > > > > + ciphertext_page,
> > > > > > + i_blocksize(inode), offs,
> > > > > > + gfp_flags);
> > > > > > + if (err)
> > > > > > + return ERR_PTR(err);
> > > >
> > > > Apparently ubifs does encrypt data shorter than the filesystem block size, so
> > > > this part is wrong.
> > > >
> > > > I suggest we split this into two functions, fscrypt_encrypt_block_inplace() and
> > > > fscrypt_encrypt_blocks(), so that it's conceptually simpler what each function
> > > > does. Currently this works completely differently depending on whether the
> > > > filesystem set FS_CFLG_OWN_PAGES in its fscrypt_operations, which is weird.
> > > >
> > > > I also noticed that using fscrypt_ctx for writes seems to be unnecessary.
> > > > AFAICS, page_private(bounce_page) could point directly to the pagecache page.
> > > > That would simplify things a lot, especially since then fscrypt_ctx could be
> > > > removed entirely after you convert reads to use read_callbacks_ctx.
> > > >
> > > > IMO, these would be worthwhile cleanups for fscrypt by themselves, without
> > > > waiting for the read_callbacks stuff to be finalized. Finalizing the
> > > > read_callbacks stuff will probably require reaching a consensus about how they
> > > > should work with future filesystem features like fsverity and compression.
> > > >
> > > > So to move things forward, I'm considering sending out a series with the above
> > > > cleanups for fscrypt, plus the equivalent of your patches:
> > > >
> > > > "fscrypt_encrypt_page: Loop across all blocks mapped by a page range"
> > > > "fscrypt_zeroout_range: Encrypt all zeroed out blocks of a page"
> > > > "Add decryption support for sub-pagesized blocks" (fs/crypto/ part only)
> > > >
> > > > Then hopefully we can get all that applied for 5.3 so that fs/crypto/ itself is
> > > > ready for blocksize != PAGE_SIZE; and get your changes to ext4_bio_write_page(),
> > > > __ext4_block_zero_page_range(), and ext4_block_write_begin() applied too, so
> > > > that ext4 is partially ready for encryption with blocksize != PAGE_SIZE.
> > > >
> > > > Then only the read_callbacks stuff will remain, to get encryption support into
> > > > fs/mpage.c and fs/buffer.c. Do you think that's a good plan?
> > >
> > > Hi Eric,
> > >
> > > IMHO, I will continue posting the next version of the current patchset and if
> > > there are no serious reservations from FS maintainers the "read callbacks"
> > > patchset can be merged. In such a scenario, the cleanups being
> > > non-complicated, can be merged later.
> > >
> >
> > Most of the patches I have in mind are actually things that are in your patchset
> > already, or have been requested, or will be requested eventually :-). I'm
> > concerned that people will keep going back and forth on this patchset for a lot
> > longer, arguing about fsverity, compression, details of the fs/crypto/ stuff,
> > etc. Moreover it's based on unmerged patches that add the fsverity feature, so
> > it can't be merged as-is anyway.
> >
> > IMO, it's also difficult for people to review the read_callbacks stuff when it's
> > mixed in with lots of other fscrypt and ext4 changes for blocksize != PAGE_SIZE.
> >
> > I actually have a patchset almost ready already, so I'm going to send it out and
> > see what you think. It *should* make things a lot easier for you, since then
> > you can base a much smaller read_callbacks patchset on top of it.
>
> One of the things that I am concerned most about is the fact that the more we
> delay merging read_callbacks patchset, the more the chances of filesystems
> adding further operations that get executed after read I/O completes. Most of
> the time, these implementations tend to have filesystem specific changes which
> are going to be very difficult (impossible?) to make them work with
> read_callback patchset. So instead of making things easier, delaying merging
> the read_callback patchset ends up actually having the opposite effect.
>
> With the read_callback patchset merged, FS feature developers will take
> read_callback framework into consideration before designing/implementing new
> related features.
>
The main problems are that your patchset mixes up conceptually unrelated
changes, and is dependent on future filesystem features. See how it starts by
adding read_callbacks support for both fscrypt *and* fsverity (the latter of
which is not merged yet), then updates fs/crypto/ to support subpage blocks,
*then* goes back and finishes read_callbacks to support buffer_heads since that
depended on the fs/crypto/ changes. The ext4 changes for subpage blocks are
mixed in too throughout the patchset. So I don't think it can proceed in its
current form; it's too much for anyone to handle at once.
And I see your first patchset for ext4 encryption with subpage blocks was sent
almost a year and a half ago, so it's indeed been going in circles for a while.
But based on your work I've been able to get the fs/crypto/ and ext4
preparations for subpage blocks into a clean set of changes by themselves.
There are needed in any case, so IMO we should take them first in order to
unblock the rest.
I don't really understand your point about forcing filesystems to be compatible
with read_callbacks. The whole point of read_callbacks is that it's a common
support layer which makes it easier for filesystems to do the things they're
doing anyway, or will be doing. So it shouldn't affect filesystem designs.
Thanks!
- Eric
next prev parent reply other threads:[~2019-05-02 18:16 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-28 4:31 [PATCH V2 00/13] Consolidate FS read I/O callbacks code Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 01/13] ext4: Clear BH_Uptodate flag on decryption error Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 02/13] Consolidate "read callbacks" into a new file Chandan Rajendra
2019-04-30 0:00 ` Eric Biggers
2019-05-01 12:30 ` Chandan Rajendra
2019-04-30 1:37 ` Chao Yu
2019-05-01 12:31 ` Chandan Rajendra
2019-04-30 18:05 ` Eric Biggers
2019-05-01 12:32 ` Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 03/13] fsverity: Add call back to decide if verity check has to be performed Chandan Rajendra
2019-04-30 21:10 ` Jeremy Sowden
2019-05-01 12:33 ` Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 04/13] fsverity: Add call back to determine readpage limit Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 05/13] fs/mpage.c: Integrate read callbacks Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 06/13] ext4: Wire up ext4_readpage[s] to use mpage_readpage[s] Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 07/13] Add decryption support for sub-pagesized blocks Chandan Rajendra
2019-04-30 0:38 ` Eric Biggers
2019-05-01 13:40 ` Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 08/13] ext4: Decrypt all boundary blocks when doing buffered write Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 09/13] ext4: Decrypt the block that needs to be partially zeroed Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 10/13] fscrypt_encrypt_page: Loop across all blocks mapped by a page range Chandan Rajendra
2019-04-30 17:11 ` Eric Biggers
2019-04-30 23:08 ` [f2fs-dev] " Eric Biggers
2019-05-01 14:49 ` Chandan Rajendra
2019-05-01 22:29 ` Eric Biggers
2019-05-02 5:52 ` Chandan Rajendra
2019-05-02 18:16 ` Eric Biggers [this message]
2019-04-28 4:31 ` [PATCH V2 11/13] ext4: Compute logical block and the page range to be encrypted Chandan Rajendra
2019-04-30 17:01 ` Eric Biggers
2019-05-01 14:11 ` Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 12/13] fscrypt_zeroout_range: Encrypt all zeroed out blocks of a page Chandan Rajendra
2019-04-30 16:51 ` Eric Biggers
2019-05-01 14:22 ` Chandan Rajendra
2019-04-28 4:31 ` [PATCH V2 13/13] ext4: Enable encryption for subpage-sized blocks Chandan Rajendra
2019-04-30 0:27 ` [PATCH V2 00/13] Consolidate FS read I/O callbacks code Matthew Wilcox
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