linux-toradex.git/kernel/module.c, branch v4.5-rc4

modules: fix longstanding /proc/kallsyms vs module insertion race.

2016-02-03T06:28:15+00:00

For CONFIG_KALLSYMS, we keep two symbol tables and two string tables.
There's one full copy, marked SHF_ALLOC and laid out at the end of the
module's init section.  There's also a cut-down version that only
contains core symbols and strings, and lives in the module's core
section.

After module init (and before we free the module memory), we switch
the mod->symtab, mod->num_symtab and mod->strtab to point to the core
versions.  We do this under the module_mutex.

However, kallsyms doesn't take the module_mutex: it uses
preempt_disable() and rcu tricks to walk through the modules, because
it's used in the oops path.  It's also used in /proc/kallsyms.
There's nothing atomic about the change of these variables, so we can
get the old (larger!) num_symtab and the new symtab pointer; in fact
this is what I saw when trying to reproduce.

By grouping these variables together, we can use a
carefully-dereferenced pointer to ensure we always get one or the
other (the free of the module init section is already done in an RCU
callback, so that's safe).  We allocate the init one at the end of the
module init section, and keep the core one inside the struct module
itself (it could also have been allocated at the end of the module
core, but that's probably overkill).

Reported-by: Weilong Chen 
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=111541
Cc: stable@kernel.org
Signed-off-by: Rusty Russell

module: wrapper for symbol name.

2016-02-03T06:28:14+00:00

This trivial wrapper adds clarity and makes the following patch
smaller.

Cc: stable@kernel.org
Signed-off-by: Rusty Russell

modules: fix modparam async_probe request

2016-02-03T06:28:14+00:00

Commit f2411da746985 ("driver-core: add driver module
asynchronous probe support") added async probe support,
in two forms:

  * in-kernel driver specification annotation
  * generic async_probe module parameter (modprobe foo async_probe)

To support the generic kernel parameter parse_args() was
extended via commit ecc8617053e0 ("module: add extra
argument for parse_params() callback") however commit
failed to f2411da746985 failed to add the required argument.

This causes a crash then whenever async_probe generic
module parameter is used. This was overlooked when the
form in which in-kernel async probe support was reworked
a bit... Fix this as originally intended.

Cc: Hannes Reinecke 
Cc: Dmitry Torokhov 
Cc: stable@vger.kernel.org (4.2+)
Signed-off-by: Luis R. Rodriguez 
Signed-off-by: Rusty Russell  [minimized]

Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching

2016-01-15T00:38:02+00:00

Pull livepatching updates from Jiri Kosina:

 - RO/NX attribute fixes for patch module relocations from Josh
   Poimboeuf.  As part of this effort, module.c has been cleaned up as
   well and livepatching is piggy-backing on this cleanup.  Rusty is OK
   with this whole lot going through livepatching tree.

 - symbol disambiguation support from Chris J Arges.  That series is
   also

        Reviewed-by: Miroslav Benes 

   but this came in only after I've alredy pushed out.  Didn't want to
   rebase because of that, hence I am mentioning it here.

 - symbol lookup fix from Miroslav Benes

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
  livepatch: Cleanup module page permission changes
  module: keep percpu symbols in module's symtab
  module: clean up RO/NX handling.
  module: use a structure to encapsulate layout.
  gcov: use within_module() helper.
  module: Use the same logic for setting and unsetting RO/NX
  livepatch: function,sympos scheme in livepatch sysfs directory
  livepatch: add sympos as disambiguator field to klp_reloc
  livepatch: add old_sympos as disambiguator field to klp_func

ftrace/module: Call clean up function when module init fails early

2016-01-07T17:17:39+00:00

If the module init code fails after calling ftrace_module_init() and before
calling do_init_module(), we can suffer from a memory leak. This is because
ftrace_module_init() allocates pages to store the locations that ftrace
hooks are placed in the module text. If do_init_module() fails, it still
calls the MODULE_GOING notifiers which will tell ftrace to do a clean up of
the pages it allocated for the module. But if load_module() fails before
then, the pages allocated by ftrace_module_init() will never be freed.

Call ftrace_release_mod() on the module if load_module() fails before
getting to do_init_module().

Link: http://lkml.kernel.org/r/567CEA31.1070507@intel.com

Reported-by: "Qiu, PeiyangX" 
Fixes: a949ae560a511 "ftrace/module: Hardcode ftrace_module_init() call into load_module()"
Cc: stable@vger.kernel.org # v2.6.38+
Acked-by: Rusty Russell 
Signed-off-by: Steven Rostedt

module: keep percpu symbols in module's symtab

2015-12-04T21:46:26+00:00

Currently, percpu symbols from .data..percpu ELF section of a module are
not copied over and stored in final symtab array of struct module.
Consequently such symbol cannot be returned via kallsyms API (for
example kallsyms_lookup_name). This can be especially confusing when the
percpu symbol is exported. Only its __ksymtab et al. are present in its
symtab.

The culprit is in layout_and_allocate() function where SHF_ALLOC flag is
dropped for .data..percpu section. There is in fact no need to copy the
section to final struct module, because kernel module loader allocates
extra percpu section by itself. Unfortunately only symbols from
SHF_ALLOC sections are copied due to a check in is_core_symbol().

The patch changes is_core_symbol() function to copy over also percpu
symbols (their st_shndx points to .data..percpu ELF section). We do it
only if CONFIG_KALLSYMS_ALL is set to be consistent with the rest of the
function (ELF section is SHF_ALLOC but !SHF_EXECINSTR). Finally
elf_type() returns type 'a' for a percpu symbol because its address is
absolute.

Signed-off-by: Miroslav Benes 
Signed-off-by: Rusty Russell 
Signed-off-by: Jiri Kosina

module: clean up RO/NX handling.

2015-12-04T21:46:26+00:00

Modules have three sections: text, rodata and writable data.  The code
handled the case where these overlapped, however they never can:
debug_align() ensures they are always page-aligned.

This is why we got away with manually traversing the pages in
set_all_modules_text_rw() without rounding.

We create three helper functions: frob_text(), frob_rodata() and
frob_writable_data().  We then call these explicitly at every point,
so it's clear what we're doing.

We also expose module_enable_ro() and module_disable_ro() for
livepatch to use.

Reviewed-by: Josh Poimboeuf 
Signed-off-by: Rusty Russell 
Signed-off-by: Jiri Kosina

module: use a structure to encapsulate layout.

2015-12-04T21:46:25+00:00

Makes it easier to handle init vs core cleanly, though the change is
fairly invasive across random architectures.

It simplifies the rbtree code immediately, however, while keeping the
core data together in the same cachline (now iff the rbtree code is
enabled).

Acked-by: Peter Zijlstra 
Reviewed-by: Josh Poimboeuf 
Signed-off-by: Rusty Russell 
Signed-off-by: Jiri Kosina

module: Use the same logic for setting and unsetting RO/NX

2015-12-04T21:46:24+00:00

When setting a module's RO and NX permissions, set_section_ro_nx() is
used, but when clearing them, unset_module_{init,core}_ro_nx() are used.
The unset functions don't have the same checks the set function has for
partial page protections.  It's probably harmless, but it's still
confusingly asymmetrical.

Instead, use the same logic to do both.  Also add some new
set_module_{init,core}_ro_nx() helper functions for more symmetry with
the unset functions.

Signed-off-by: Josh Poimboeuf 
Signed-off-by: Rusty Russell 
Signed-off-by: Jiri Kosina

module: Fix locking in symbol_put_addr()

2015-08-24T01:07:01+00:00

Poma (on the way to another bug) reported an assertion triggering:

  [] module_assert_mutex_or_preempt+0x49/0x90
  [] __module_address+0x32/0x150
  [] __module_text_address+0x16/0x70
  [] symbol_put_addr+0x29/0x40
  [] dvb_frontend_detach+0x7d/0x90 [dvb_core]

Laura Abbott  produced a patch which lead us to
inspect symbol_put_addr(). This function has a comment claiming it
doesn't need to disable preemption around the module lookup
because it holds a reference to the module it wants to find, which
therefore cannot go away.

This is wrong (and a false optimization too, preempt_disable() is really
rather cheap, and I doubt any of this is on uber critical paths,
otherwise it would've retained a pointer to the actual module anyway and
avoided the second lookup).

While its true that the module cannot go away while we hold a reference
on it, the data structure we do the lookup in very much _CAN_ change
while we do the lookup. Therefore fix the comment and add the
required preempt_disable().

Reported-by: poma 
Signed-off-by: Peter Zijlstra (Intel) 
Signed-off-by: Rusty Russell 
Fixes: a6e6abd575fc ("module: remove module_text_address()")
Cc: stable@kernel.org