On 30/4/20 9:03 am, Linus Torvalds wrote:
On Wed, Apr 29, 2020 at 2:57 PM Russell King - ARM Linux admin
<linux@xxxxxxxxxxxxxxx> wrote:
I've never had any reason to use FDPIC, and I don't have any binaries
that would use it. Nicolas Pitre added ARM support, so I guess he
would be the one to talk to about it. (Added Nicolas.)
While we're at it, is there anybody who knows binfmt_flat?
It might be Nicolas too.
binfmt_flat doesn't do core-dumping, but it has some other oddities.
In particular, I'd like to bring sanity to the installation of the new
creds, and all the _normal_ binfmt cases do it largely close together
with setup_new_exec().
binfmt_flat is doing odd things. It's doing this:
/* Flush all traces of the currently running executable */
if (id == 0) {
ret = flush_old_exec(bprm);
if (ret)
goto err;
/* OK, This is the point of no return */
set_personality(PER_LINUX_32BIT);
setup_new_exec(bprm);
}
in load_flat_file() - which is also used to loading _libraries_. Where
it makes no sense at all.
I haven't looked at the shared lib support in there for a long time,
but I thought that "id" is only 0 for the actual final program.
Libraries have a slot or id number associated with them.
It does the
install_exec_creds(bprm);
in load_flat_binary() (which makes more sense: that is only for actual
binary loading, no library case).
I would _like_ for every binfmt loader to do
/* Flush all traces of the currently running executable */
retval = flush_old_exec(bprm);
if (retval)
return retval;
.. possibly set up personalities here ..
setup_new_exec(bprm);
install_exec_creds(bprm);
all together, and at least merge 'setup_new_exec()' with 'install_exec_creds()'.
And I think all the binfmt handlers would be ok with that, but the
flat one in particular is really oddly set up.
*Particularly* with that flush_old_exec/setup_new_exec() being done by
the same routine that is also loading libraries (and called from
'calc_reloc()' from binary loading too).
Adding Greg Ungerer for m68knommu. Can somebody sort out why that
flush_old_exec/setup_new_exec() isn't in load_flat_binary() like
install_exec_creds() is?
Most of that file goes back to pre-git days. And most of the commits
since are not so much about binfmt_flat, as they are about cleanups or
changes elsewhere where binfmt_flat was just a victim.
I'll have a look at this.
Quick hack test shows moving setup_new_exec(bprm) to be just before
install_exec_creds(bprm) works fine for the static binaries case.
Doing the flush_old_exec(bprm) there too crashed out - I'll need to
dig into that to see why.
Regards
Greg
