linux-kernel - Re: [PATCH v4 4/5] binfmt_elf, binfmt_elf

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Date:   Wed, 26 Aug 2020 10:14:51 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Jann Horn <jannh@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux-MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH v4 4/5] binfmt_elf, binfmt_elf_fdpic: Use a VMA list snapshot

On Wed, Aug 26, 2020 at 8:15 AM Jann Horn <jannh@...gle.com> wrote:
>
> A downside of this approach is that we now need a bigger amount of kernel
> memory per userspace VMA in the normal ELF case, and that we need O(n)
> kernel memory in the FDPIC ELF case at all; but 40 bytes per VMA shouldn't
> be terribly bad.

So this looks much simpler now.

But it also makes it more obvious how that dump-size callback is kind
of pointless. Why does elf_fdpic have different heuristics than
regular elf? And not in meaningful ways - the heuristics look
basically identical, just with different logging and probably random
other differences that  have mostly just grown over time.

So rather than the callback function pointer, I think you should just
copy the ELF version of the dump_size() logic, and get rid of a very
odd and strange callback.

But even in this form, at least this patch doesn't make the code look
_worse_ than it used to, so while I would like to see a further
cleanup I no longer dislike it.

              Linus