From: Alexey Dobriyan <adobriyan@gmail.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] elf: fix "start_code" evaluation
Date: Thu, 23 May 2019 22:35:05 +0300 [thread overview]
Message-ID: <20190523193505.GA8475@avx2> (raw)
In-Reply-To: <20190523114417.f99d781754ed22950115c64a@linux-foundation.org>
On Thu, May 23, 2019 at 11:44:17AM -0700, Andrew Morton wrote:
> On Thu, 23 May 2019 20:57:36 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
>
> > Only executable ELF program headers should change ->start_code.
> >
> > ...
> >
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1026,7 +1026,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> > }
> > }
> > k = elf_ppnt->p_vaddr;
> > - if (k < start_code)
> > + if ((elf_ppnt->p_flags & PF_X) && k < start_code)
> > start_code = k;
> > if (start_data < k)
> > start_data = k;
>
> What problem does this solve?
It is a bug. Look at the ->end_code update:
if ((elf_ppnt->p_flags & PF_X) && end_code < k)
end_code = k;
> How does it alter runtime behaviour?
It makes "VmExe" and "VmLib" accounting more accurate for common case.
> How do we know it won't break anything?
We don't. Some distros are unaffected because they ship binaries with
first PT_LOAD segment being executable (Debian 8). Some don't.
Regardless, these fields are lies: ELF binary can have multiple disjoint
PT_LOAD segments, but all those ->start and ->end fields assume everything
is mapped together.
Hopefully nobody actually uses them for anything serious.
prev parent reply other threads:[~2019-05-23 19:35 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-23 17:57 [PATCH] elf: fix "start_code" evaluation Alexey Dobriyan
2019-05-23 18:44 ` Andrew Morton
2019-05-23 19:35 ` Alexey Dobriyan [this message]
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