linux-kernel - Re: [PATCH v2 23/28] binder: document the final page calculation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20231204115727.42370-1-aliceryhl@google.com>
Date:   Mon,  4 Dec 2023 11:57:27 +0000
From:   Alice Ryhl <aliceryhl@...gle.com>
To:     cmllamas@...gle.com
Cc:     arve@...roid.com, brauner@...nel.org, gregkh@...uxfoundation.org,
        joel@...lfernandes.org, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, maco@...roid.com, surenb@...gle.com,
        tkjos@...roid.com
Subject: Re: [PATCH v2 23/28] binder: document the final page calculation

> The code to determine the page range for binder_lru_freelist_del() is
> quite obscure. It leverages the buffer_size calculated before doing an
> oversized buffer split. This is used to figure out if the last page is
> being shared with another active buffer. If so, the page gets trimmed
> out of the range as it has been previously removed from the freelist.
> 
> This would be equivalent to getting the start page of the next in-use
> buffer explicitly. However, the code for this is much larger as we can
> see in binder_free_buf_locked() routine. Instead, lets settle on
> documenting the tricky step and using better names for now.
> 
> I believe an ideal solution would be to count the binder_page->users to
> determine when a page should be added or removed from the freelist.
> However, this is a much bigger change than what I'm willing to risk at
> this time.
> 
> Signed-off-by: Carlos Llamas <cmllamas@...gle.com>

Yes, this does help somewhat.

However, `curr_last_page` is actually not the last page. It's the last
page plus one, since `binder_lru_freelist_del` is exclusive on this
argument. Maybe rename it to `curr_after_last_page` or something like
that? Or maybe even just `curr_last_page_plus_one`.

Alice