Bug 1574923

We also have this:

0000000000401c71 <static_reloc.c_end>:
  401c71:       66                      data16

0000000000401c72 <static_reloc.c>:
  401c72:       2e 0f 1f 84 00 00 00    nopl   %cs:0x0(%rax,%rax,1)
  401c79:       00 00 
  401c7b:       0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)

This confuses eu-checksec:

Hardened: eu-checksec: GAP detected in annobin notes: 401c72 .. 401d30.

Hi Florian,

> Linking a program against a glibc which has been built with full annobin
> support results in this statically linked bits being copied over:
> 
> 00000000004052c0 <__libc_csu_init>:
>   4052c0:       41 57                   push   %r15
> 
> 00000000004052c2 <elf_init.c>:
>   4052c2:       49 89 d7                mov    %rdx,%r15

> The elf_init.c symbol looks very much out of place.

This happens because annobin now creates a start-of-file symbol that is
actually two bytes in from the start of the file.  This is on the
assumption that this offset will prevent the symbol from overlapping the
function symbol for the first function in the file, and so stop the
problems associated with having two symbols for the same address.

Is the presence of this symbol merely an inconvenience, or is it actually
breaking something ?  Apart from the disassembler output that is, which I
agree is wrong.

One thing I could try is to move the annobin file start symbol two bytes
prior to the start of the file...  Although this might cause problems with
the end of the disassembly of the code that is prior to elf_init.c in the
application's address space. :-(


(In reply to Florian Weimer from comment #1)
> We also have this:
> 
> 0000000000401c71 <static_reloc.c_end>:
>   401c71:       66                      data16
> 
> 0000000000401c72 <static_reloc.c>:
>   401c72:       2e 0f 1f 84 00 00 00    nopl   %cs:0x0(%rax,%rax,1)

Hang on - how did the end-of-file symbol end up being before the
start-of-file symbol ?


> This confuses eu-checksec:

Well yes, I am confused too.  Is there something funky going on in the
source for static_reloc.c ?  Some section pushing and popping maybe ?

Cheers
  Nick

(In reply to Nick Clifton from comment #2)
> (In reply to Florian Weimer from comment #1)
> > We also have this:
> > 
> > 0000000000401c71 <static_reloc.c_end>:
> >   401c71:       66                      data16
> > 
> > 0000000000401c72 <static_reloc.c>:
> >   401c72:       2e 0f 1f 84 00 00 00    nopl   %cs:0x0(%rax,%rax,1)
> 
> Hang on - how did the end-of-file symbol end up being before the
> start-of-file symbol ?

I think it's because the end symbol is not biased, only the start symbol.

The biasing looks wrong to me because it makes the covered PC range incorrect.

> Well yes, I am confused too.  Is there something funky going on in the
> source for static_reloc.c ?  Some section pushing and popping maybe ?

Not really, as far as I can see, it is just an empty file, or maybe it contains a single empty function (not sure about the compiler flags here).  I can reproduce it with small input files:

    38: 00000000004004e3     0 NOTYPE  LOCAL  DEFAULT   12 m.c
    39: 00000000004004e1     0 NOTYPE  LOCAL  DEFAULT   12 m.c_end

$ cat m.c
main() { }

That's wrong on a different level because the main function is *outside* this range:

    77: 00000000004003e0     3 FUNC    GLOBAL DEFAULT   12 main

> Is the presence of this symbol merely an inconvenience, or is it actually
> breaking something ?  Apart from the disassembler output that is, which I
> agree is wrong.

It's worse if the symbol is in the middle of the instruction because it can happen that this corrupts the disassembler output.

I have added a patch to the rawhide annobin which appears to resolve this
problem.  (By making the annobin file symbol hidden).  I would like to leave
it a few days however before backporting to F28, just to make sure that it
really does work, and that it does not break anything.

Fixed in: annobin-5.8-1.fc29

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bugs or makes them obsolete.

This message is a reminder that Fedora 28 is nearing its end of life.
On 2019-May-28 Fedora will stop maintaining and issuing updates for
Fedora 28. It is Fedora's policy to close all bug reports from releases
that are no longer maintained. At that time this bug will be closed as
EOL if it remains open with a Fedora 'version' of '28'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version' 
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not 
able to fix it before Fedora 28 is end of life. If you would still like 
to see this bug fixed and are able to reproduce it against a later version 
of Fedora, you are encouraged  change the 'version' to a later Fedora 
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's 
lifetime, sometimes those efforts are overtaken by events. Often a 
more recent Fedora release includes newer upstream software that fixes 
bugs or makes them obsolete.

Fedora 28 changed to end-of-life (EOL) status on 2019-05-28. Fedora 28 is
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