From: Christian Brauner <brauner@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
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Subject: Re: [PATCH 87/87] fs: move i_blocks up a few places in struct inode
Date: Fri, 29 Sep 2023 11:32:49 +0200 [thread overview]
Message-ID: <20230929-keimt-umspannen-bfd12d2c2033@brauner> (raw)
In-Reply-To: <CAHk-=wij_42Q9WHY898r-gugmT5c-1JJKRh3C+nTUd1hc1aeqQ@mail.gmail.com>
On Thu, Sep 28, 2023 at 10:41:34AM -0700, Linus Torvalds wrote:
> On Thu, 28 Sept 2023 at 04:06, Jeff Layton <jlayton@kernel.org> wrote:
> >
> > Move i_blocks up above the i_lock, which moves the new 4 byte hole to
> > just after the timestamps, without changing the size of the structure.
>
> I'm sure others have mentioned this, but 'struct inode' is marked with
> __randomize_layout, so the actual layout may end up being very
> different.
>
> I'm personally not convinced the whole structure randomization is
> worth it - it's easy enough to figure out for any distro kernel since
> the seed has to be the same across machines for modules to work, so
> even if the seed isn't "public", any layout is bound to be fairly
> easily discoverable.
>
> So the whole randomization only really works for private kernel
> builds, and it adds this kind of pain where "optimizing" the structure
> layout is kind of pointless depending on various options.
>
> I certainly *hope* no distro enables that pointless thing, but it's a worry.
They don't last we checked. Just last cycle we moved stuff in struct
file around to optimize things and we explicitly said we don't give a
damn about struct randomization. Anyone who enables this will bleed
performance pretty badly, I would reckon.
prev parent reply other threads:[~2023-09-29 10:54 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-28 11:05 [PATCH 85/87] fs: rename i_atime and i_mtime fields to __i_atime and __i_mtime Jeff Layton
2023-09-28 11:05 ` [PATCH 86/87] fs: switch timespec64 fields in inode to discrete integers Jeff Layton
2023-09-28 15:48 ` Arnd Bergmann
2023-09-28 17:06 ` Jeff Layton
2023-09-28 17:19 ` Darrick J. Wong
2023-09-28 17:40 ` Jeff Layton
2023-09-28 20:21 ` Arnd Bergmann
2023-09-28 21:26 ` Theodore Ts'o
2023-09-29 0:18 ` Linus Torvalds
2023-09-29 3:50 ` Amir Goldstein
2023-09-29 16:22 ` Linus Torvalds
2023-09-29 3:27 ` Amir Goldstein
2023-09-29 6:32 ` David Howells
2023-09-30 14:50 ` Steve French
2023-10-01 5:01 ` [OT] " Gabriel Paubert
2023-09-29 9:44 ` Christian Brauner
2023-09-29 10:16 ` Jeff Layton
2023-09-28 17:09 ` Jeff Layton
2023-09-28 11:05 ` [PATCH 87/87] fs: move i_blocks up a few places in struct inode Jeff Layton
2023-09-28 11:35 ` Amir Goldstein
2023-09-28 12:01 ` Jeff Layton
2023-09-28 17:41 ` Linus Torvalds
2023-09-28 18:01 ` Jeff Layton
2023-09-29 9:32 ` Christian Brauner [this message]
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