From: Kees Cook <keescook@chromium.org>
To: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Bob Copeland <me@bobcopeland.com>,
linux-karma-devel@lists.sourceforge.net,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH][next] fs: omfs: Use flexible-array member in struct omfs_extent
Date: Mon, 17 Jul 2023 08:20:22 -0700 [thread overview]
Message-ID: <202307170758.14B5D83D@keescook> (raw)
In-Reply-To: <ZLGodUeD307GlINN@work>
On Fri, Jul 14, 2023 at 01:56:37PM -0600, Gustavo A. R. Silva wrote:
> There are some binary differences before and after changes, but this are
> expected due to the change in the size of 'struct omfs_extent' and the
> necessary adjusments.
For binary changes, I think commit logs should have more details. In
this case, I can figure it out:
> diff --git a/fs/omfs/file.c b/fs/omfs/file.c
> index de8f57ee39ec..6b580b9da8e3 100644
> --- a/fs/omfs/file.c
> +++ b/fs/omfs/file.c
> @@ -14,7 +14,7 @@ static u32 omfs_max_extents(struct omfs_sb_info *sbi, int offset)
> {
> return (sbi->s_sys_blocksize - offset -
> sizeof(struct omfs_extent)) /
> - sizeof(struct omfs_extent_entry) + 1;
> + sizeof(struct omfs_extent_entry);
> }
I think the original calculation meant to do:
return (sbi->s_sys_blocksize - offset -
(sizeof(struct omfs_extent) - sizeof(struct omfs_extent_entry))) /
sizeof(struct omfs_extent_entry);
So this binary difference looks correct. I rebuilt before/after this
patch with omfs_max_extents() marked as noinline, and all the binary
changes were isolated here, and did exactly as expected: the first half
is 16 smaller (size of struct omfs_extent_entry), and the final +1 is
removed:
- 2e1: lea -0x20(%rbx),%rax
+ 2e1: lea -0x10(%rbx),%rax
2e5: pop %rbx
2e6: pop %rbp
2e7: shr $0x4,%rax
- 2eb: add $0x1,%eax
So this looks correct to me. Thanks!
Reviewed-by: Kees Cook <keescook@chromium.org>
--
Kees Cook
next prev parent reply other threads:[~2023-07-17 15:21 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-14 19:56 [PATCH][next] fs: omfs: Use flexible-array member in struct omfs_extent Gustavo A. R. Silva
2023-07-17 15:20 ` Kees Cook [this message]
2023-07-19 13:03 ` Bob Copeland
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=202307170758.14B5D83D@keescook \
--to=keescook@chromium.org \
--cc=gustavoars@kernel.org \
--cc=linux-hardening@vger.kernel.org \
--cc=linux-karma-devel@lists.sourceforge.net \
--cc=linux-kernel@vger.kernel.org \
--cc=me@bobcopeland.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).