MIME-Version: 1.0
References: <20211211173447.4155374-1-hjl.tools@gmail.com> <CACVxJT-k664=aYp4VkG1LH3PsGHEf50PqP5EA+JWiFVb_JVs2Q@mail.gmail.com>
 <CAMe9rOqM+S_uBO-t5jJ1TLVD0R-LOJEiR6htb+k05c+ak7gF-g@mail.gmail.com>
 <CAHk-=wiEgwj3DGZai2GF9+z-FCSS455kGZ9z2g1qtdPLPWpvxQ@mail.gmail.com>
 <CAMe9rOqYxiMabie_2LN2mTTP7QPa0_mfKwDY10OSzKFj5GYT7A@mail.gmail.com> <CAHk-=whPK-aB34T1YS4CVK0G1m6QU7FZg28+oEeVaGy-b4hZGA@mail.gmail.com>
In-Reply-To: <CAHk-=whPK-aB34T1YS4CVK0G1m6QU7FZg28+oEeVaGy-b4hZGA@mail.gmail.com>
From:   "H.J. Lu" <hjl.tools@gmail.com>
Date:   Sun, 12 Dec 2021 11:30:01 -0800
Message-ID: <CAMe9rOoqkH=FL3s331YKeyz_Qjf7pR9M_Cf117XHErrTU-2iRA@mail.gmail.com>
Subject: Re: [PATCH] fs/binfmt_elf.c: disallow zero entry point address
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Sun, Dec 12, 2021 at 11:15 AM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Sun, Dec 12, 2021 at 11:06 AM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > According to the ELF specification, zero entry point value means
> > there is no entry point.  Such ELF binary doesn't conform to the
> > ELF specification.
>
> Nobody cares about paper specifications.
>
> All that matters is REALITY.
>
> So let me quote my email again, since you clearly didn't actually read
> it (read that "maybe it's not supposed to work" part):
>
> > That's not my main worry - what if somebody has a code section with a
> > zero vaddr and intentionally put the entry at the beginning?
> >
> > Maybe it's not supposed to work by some paper standatd, but afaik
> > currently it _would_ work.
>
> I'm not sure this can happen currently (maybe all tools effectively
> make it so that the ELF headers etc are part of the loaded image).
>
> But no, paper specifications have absolutely no meaning if they don't
> match realty.
>
> And the reality is that I don't think we've ever checked e_entry being
> zero, which means that maybe people have used it.
>
> So convince me that the above cannot happen. I'm perfectly willing to
> be convinced, but "some random paper standard that we've never
> followed" is not the thing to quote.
>

On Linux, the start of the first PT_LOAD segment is the ELF
header and the address 0 points to the ELF magic bytes which
isn't a valid code sequence.

-- 
H.J.