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From:   Florian Weimer <fweimer@redhat.com>
To:     Szabolcs Nagy <szabolcs.nagy@arm.com>
Cc:     libc-alpha@sourceware.org, Jeremy Linton <jeremy.linton@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Mark Brown <broonie@kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Salvatore Mesoraca <s.mesoraca16@gmail.com>,
        Lennart Poettering <mzxreary@0pointer.de>,
        Topi Miettinen <toiwoton@gmail.com>,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kernel-hardening@lists.openwall.com,
        linux-hardening@vger.kernel.org, "H.J. Lu" <hjl.tools@gmail.com>
Subject: Re: [PATCH 2/4] elf: Move note processing after l_phdr is updated
 [BZ #26831]
References: <cover.1604393169.git.szabolcs.nagy@arm.com>
        <7b008fd34f802456db3731a043ff56683b569ff7.1604393169.git.szabolcs.nagy@arm.com>
Date:   Tue, 03 Nov 2020 11:38:03 +0100
In-Reply-To: <7b008fd34f802456db3731a043ff56683b569ff7.1604393169.git.szabolcs.nagy@arm.com>
        (Szabolcs Nagy's message of "Tue, 3 Nov 2020 10:26:18 +0000")
Message-ID: <87r1pabu9g.fsf@oldenburg2.str.redhat.com>
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* Szabolcs Nagy:

> Program headers are processed in two pass: after the first pass
> load segments are mmapped so in the second pass target specific
> note processing logic can access the notes.
>
> The second pass is moved later so various link_map fields are
> set up that may be useful for note processing such as l_phdr.
> ---
>  elf/dl-load.c | 30 +++++++++++++++---------------
>  1 file changed, 15 insertions(+), 15 deletions(-)
>
> diff --git a/elf/dl-load.c b/elf/dl-load.c
> index ceaab7f18e..673cf960a0 100644
> --- a/elf/dl-load.c
> +++ b/elf/dl-load.c
> @@ -1259,21 +1259,6 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd,
>  				  maplength, has_holes, loader);
>      if (__glibc_unlikely (errstring != NULL))
>        goto call_lose;
> -
> -    /* Process program headers again after load segments are mapped in
> -       case processing requires accessing those segments.  Scan program
> -       headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
> -       exits.  */
> -    for (ph = &phdr[l->l_phnum]; ph != phdr; --ph)
> -      switch (ph[-1].p_type)
> -	{
> -	case PT_NOTE:
> -	  _dl_process_pt_note (l, fd, &ph[-1]);
> -	  break;
> -	case PT_GNU_PROPERTY:
> -	  _dl_process_pt_gnu_property (l, fd, &ph[-1]);
> -	  break;
> -	}
>    }
>  
>    if (l->l_ld == 0)
> @@ -1481,6 +1466,21 @@ cannot enable executable stack as shared object requires");
>      /* Assign the next available module ID.  */
>      l->l_tls_modid = _dl_next_tls_modid ();
>  
> +  /* Process program headers again after load segments are mapped in
> +     case processing requires accessing those segments.  Scan program
> +     headers backward so that PT_NOTE can be skipped if PT_GNU_PROPERTY
> +     exits.  */
> +  for (ph = &l->l_phdr[l->l_phnum]; ph != l->l_phdr; --ph)
> +    switch (ph[-1].p_type)
> +      {
> +      case PT_NOTE:
> +	_dl_process_pt_note (l, fd, &ph[-1]);
> +	break;
> +      case PT_GNU_PROPERTY:
> +	_dl_process_pt_gnu_property (l, fd, &ph[-1]);
> +	break;
> +      }
> +
>  #ifdef DL_AFTER_LOAD
>    DL_AFTER_LOAD (l);
>  #endif

Is this still compatible with the CET requirements?

I hope it is because the CET magic happens in _dl_open_check, so after
the the code in elf/dl-load.c has run.

Thanks,
Florian
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