Change livepatch to use a basic per-task consistency model.  This is the
foundation which will eventually enable us to patch those ~10% of
security patches which change function or data semantics.  This is the
biggest remaining piece needed to make livepatch more generally useful.

This code stems from the design proposal made by Vojtech [1] in November
2014.  It's a hybrid of kGraft and kpatch: it uses kGraft's per-task
consistency and syscall barrier switching combined with kpatch's stack
trace switching.  There are also a number of fallback options which make
it quite flexible.

Patches are applied on a per-task basis, when the task is deemed safe to
switch over.  When a patch is enabled, livepatch enters into a
transition state where tasks are converging to the patched state.
Usually this transition state can complete in a few seconds.  The same
sequence occurs when a patch is disabled, except the tasks converge from
the patched state to the unpatched state.

An interrupt handler inherits the patched state of the task it
interrupts.  The same is true for forked tasks: the child inherits the
patched state of the parent.

Livepatch uses several complementary approaches to determine when it's
safe to patch tasks:

1. The first and most effective approach is stack checking of sleeping
   tasks.  If no affected functions are on the stack of a given task,
   the task is patched.  In most cases this will patch most or all of
   the tasks on the first try.  Otherwise it'll keep trying
   periodically.  This option is only available if the architecture has
   reliable stacks (HAVE_RELIABLE_STACKTRACE).

2. The second approach, if needed, is kernel exit switching.  A
   task is switched when it returns to user space from a system call, a
   user space IRQ, or a signal.  It's useful in the following cases:

   a) Patching I/O-bound user tasks which are sleeping on an affected
      function.  In this case you have to send SIGSTOP and SIGCONT to
      force it to exit the kernel and be patched.
   b) Patching CPU-bound user tasks.  If the task is highly CPU-bound
      then it will get patched the next time it gets interrupted by an
      IRQ.
   c) In the future it could be useful for applying patches for
      architectures which don't yet have HAVE_RELIABLE_STACKTRACE.  In
      this case you would have to signal most of the tasks on the
      system.  However this isn't supported yet because there's
      currently no way to patch kthreads without
      HAVE_RELIABLE_STACKTRACE.

3. For idle "swapper" tasks, since they don't ever exit the kernel, they
   instead have a klp_update_patch_state() call in the idle loop which
   allows them to be patched before the CPU enters the idle state.

   (Note there's not yet such an approach for kthreads.)

All the above approaches may be skipped by setting the 'immediate' flag
in the 'klp_patch' struct, which will disable per-task consistency and
patch all tasks immediately.  This can be useful if the patch doesn't
change any function or data semantics.  Note that, even with this flag
set, it's possible that some tasks may still be running with an old
version of the function, until that function returns.

There's also an 'immediate' flag in the 'klp_func' struct which allows
you to specify that certain functions in the patch can be applied
without per-task consistency.  This might be useful if you want to patch
a common function like schedule(), and the function change doesn't need
consistency but the rest of the patch does.

For architectures which don't have HAVE_RELIABLE_STACKTRACE, the user
must set patch->immediate which causes all tasks to be patched
immediately.  This option should be used with care, only when the patch
doesn't change any function or data semantics.

In the future, architectures which don't have HAVE_RELIABLE_STACKTRACE
may be allowed to use per-task consistency if we can come up with
another way to patch kthreads.

The /sys/kernel/livepatch/<patch>/transition file shows whether a patch
is in transition.  Only a single patch (the topmost patch on the stack)
can be in transition at a given time.  A patch can remain in transition
indefinitely, if any of the tasks are stuck in the initial patch state.

A transition can be reversed and effectively canceled by writing the
opposite value to the /sys/kernel/livepatch/<patch>/enabled file while
the transition is in progress.  Then all the tasks will attempt to
converge back to the original patch state.

[1] https://lkml.kernel.org/r/20141107140458.GA21774@suse.czSigned-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Acked-by: Ingo Molnar <mingo@kernel.org>        # for the scheduler changes
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

For the consistency model we'll need to know the sizes of the old and
new functions to determine if they're on the stacks of any tasks.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

The sysfs enabled value is a boolean, so kstrtobool() is a better fit
for parsing the input string since it does the range checking for us.
Suggested-by: NPetr Mladek <pmladek@suse.com>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Move functions related to the actual patching of functions and objects
into a new patch.c file.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

klp_patch_object()'s callers already ensure that the object is loaded,
so its call to klp_is_object_loaded() is unnecessary.

This will also make it possible to move the patching code into a
separate file.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Once we have a consistency model, patches and their objects will be
enabled and disabled at different times.  For example, when a patch is
disabled, its loaded objects' funcs can remain registered with ftrace
indefinitely until the unpatching operation is complete and they're no
longer in use.

It's less confusing if we give them different names: patches can be
enabled or disabled; objects (and their funcs) can be patched or
unpatched:

- Enabled means that a patch is logically enabled (but not necessarily
  fully applied).

- Patched means that an object's funcs are registered with ftrace and
  added to the klp_ops func stack.

Also, since these states are binary, represent them with booleans
instead of ints.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Reviewed-by: NKamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Create temporary stubs for klp_update_patch_state() so we can add
TIF_PATCH_PENDING to different architectures in separate patches without
breaking build bisectability.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

There's no reliable way to determine which module tainted the kernel
with TAINT_LIVEPATCH.  For example, /sys/module/<klp module>/taint
doesn't report it.  Neither does the "mod -t" command in the crash tool.

Make it crystal clear who the guilty party is by associating
TAINT_LIVEPATCH with any module which sets the "livepatch" modinfo
attribute.  The flag will still get set in the kernel like before, but
now it also sets the same flag in mod->taint.

Note that now the taint flag gets set when the module is loaded rather
than when it's enabled.

I also renamed find_livepatch_modinfo() to check_modinfo_livepatch() to
better reflect its purpose: it's basically a livepatch-specific
sub-function of check_modinfo().
Reported-by: NChunyu Hu <chuhu@redhat.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Acked-by: NJessica Yu <jeyu@redhat.com>
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Introduce arch_klp_init_object_loaded() to complete any additional
arch-specific tasks during patching. Architecture code may override this
function.
Signed-off-by: NJessica Yu <jeyu@redhat.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NMiroslav Benes <mbenes@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Add ro_after_init support for modules by adding a new page-aligned section
in the module layout (after rodata) for ro_after_init data and enabling RO
protection for that section after module init runs.
Signed-off-by: NJessica Yu <jeyu@redhat.com>
Acked-by: NKees Cook <keescook@chromium.org>
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>

Current object-walking helper checks the presence of obj->funcs to
determine the end of objs array in klp_object structure. This is
somewhat fragile because one can easily forget about funcs definition
during livepatch creation. In such a case the livepatch module is
successfully loaded and all objects after the incorrect one are omitted.
This is very confusing. Let's make the helper more robust and check also
for the other external member, name. Thus the helper correctly stops on
an empty item of the array. We need to have a check for obj->funcs in
klp_init_object() to make it work.

The same applies to a func-walking helper.

As a benefit we'll check for new_func member definition during the
livepatch initialization. There is no such check anywhere in the code
now.

[jkosina@suse.cz: fix shortlog]
Signed-off-by: NMiroslav Benes <mbenes@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NJessica Yu <jeyu@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

When livepatch tries to patch a function it takes the function address
and asks ftrace to install the livepatch handler at that location.
ftrace will look for an mcount call site at that exact address.

On powerpc the mcount location is not the first instruction of the
function, and in fact it's not at a constant offset from the start of
the function. To accommodate this add a hook which arch code can
override to customise the behaviour.
Signed-off-by: NTorsten Duwe <duwe@suse.de>
Signed-off-by: NBalbir Singh <bsingharora@gmail.com>
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

Commit 425595a7 ("livepatch: reuse module loader code to write
relocations") adds a possibility of dereferncing pointers supplied by the
consumer of the livepatch API before sanity (NULL) checking them (patch
and patch->mod).

Spotted by smatch tool.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NJessica Yu <jeyu@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Reuse module loader code to write relocations, thereby eliminating the need
for architecture specific relocation code in livepatch. Specifically, reuse
the apply_relocate_add() function in the module loader to write relocations
instead of duplicating functionality in livepatch's arch-dependent
klp_write_module_reloc() function.

In order to accomplish this, livepatch modules manage their own relocation
sections (marked with the SHF_RELA_LIVEPATCH section flag) and
livepatch-specific symbols (marked with SHN_LIVEPATCH symbol section
index). To apply livepatch relocation sections, livepatch symbols
referenced by relocs are resolved and then apply_relocate_add() is called
to apply those relocations.

In addition, remove x86 livepatch relocation code and the s390
klp_write_module_reloc() function stub. They are no longer needed since
relocation work has been offloaded to module loader.

Lastly, mark the module as a livepatch module so that the module loader
canappropriately identify and initialize it.
Signed-off-by: NJessica Yu <jeyu@redhat.com>
Reviewed-by: NMiroslav Benes <mbenes@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>   # for s390 changes
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Remove the livepatch module notifier in favor of directly enabling and
disabling patches to modules in the module loader. Hard-coding the
function calls ensures that ftrace_module_enable() is run before
klp_module_coming() during module load, and that klp_module_going() is
run before ftrace_release_mod() during module unload. This way, ftrace
and livepatch code is run in the correct order during the module
load/unload sequence without dependence on the module notifier call chain.
Signed-off-by: NJessica Yu <jeyu@redhat.com>
Reviewed-by: NPetr Mladek <pmladek@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

klp_find_callback() stops the search when sympos is not defined and
a second symbol of the same name is found. It means that the current
error message about the unresolvable ambiguity always prints "(2 matches)".

Let's remove this information. The total number of occurrences is
not much helpful. The author of the patch still must put a non-trivial
effort into searching the right position in the object file.

[jkosina@suse.cz: fixed grammar as suggested by Josh]
Signed-off-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NChris J Arges <chris.j.arges@canonical.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Calling set_memory_rw() and set_memory_ro() for every iteration of the
loop in klp_write_object_relocations() is messy, inefficient, and
error-prone.

Change all the read-only pages to read-write before the loop and convert
them back to read-only again afterwards.
Suggested-by: NMiroslav Benes <mbenes@suse.cz>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

The following directory structure will allow for cases when the same
function name exists in a single object.
	/sys/kernel/livepatch/<patch>/<object>/<function,sympos>

The sympos number corresponds to the nth occurrence of the symbol name in
kallsyms for the patched object.

An example of patching multiple symbols can be found here:
	https://github.com/dynup/kpatch/issues/493Signed-off-by: NChris J Arges <chris.j.arges@canonical.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

In cases of duplicate symbols, sympos will be used to disambiguate instead
of val. By default sympos will be 0, and patching will only succeed if
the symbol is unique. Specifying a positive value will ensure that
occurrence of the symbol in kallsyms for the patched object will be used
for patching if it is valid. For external relocations sympos is not
supported.

Remove klp_verify_callback, klp_verify_args and klp_verify_vmlinux_symbol
as they are no longer used.

From the klp_reloc structure remove val, as it can be refactored as a
local variable in klp_write_object_relocations.
Signed-off-by: NChris J Arges <chris.j.arges@canonical.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Currently, patching objects with duplicate symbol names fail because the
creation of the sysfs function directory collides with the previous
attempt. Appending old_addr to the function name is problematic as it
reveals the address of the function being patch to a normal user. Using
the symbol's occurrence in kallsyms to postfix the function name in the
sysfs directory solves the issue of having consistent unique names and
ensuring that the address is not exposed to a normal user.

In addition, using the symbol position as the user's method to disambiguate
symbols instead of addr allows for disambiguating symbols in modules as
well for both function addresses and for relocs. This also simplifies much
of the code. Special handling for kASLR is no longer needed and can be
removed. The klp_find_verify_func_addr function can be replaced by
klp_find_object_symbol, and klp_verify_vmlinux_symbol and its callback can
be removed completely.

In cases of duplicate symbols, old_sympos will be used to disambiguate
instead of old_addr. By default old_sympos will be 0, and patching will
only succeed if the symbol is unique. Specifying a positive value will
ensure that occurrence of the symbol in kallsyms for the patched object
will be used for patching if it is valid.

In addition, make old_addr an internal structure field not to be specified
by the user. Finally, remove klp_find_verify_func_addr as it can be
replaced by klp_find_object_symbol directly.

Support for symbol position disambiguation for relocations is added in the
next patch in this series.
Signed-off-by: NChris J Arges <chris.j.arges@canonical.com>
Reviewed-by: NPetr Mladek <pmladek@suse.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

With kASLR enabled, old_addr provided by patch module is being shifted
accrodingly so that the symbol lookups work. To have module relocations
handled properly as well, the same transformation needs to be perfomed
on relocation address information.

[jkosina@suse.cz: extended / reworded changelog a bit]
Reported-by: NCyril B. <cbay@alwaysdata.com>
Signed-off-by: NZhou Chengming <zhouchengming1@huawei.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

In case of func->state or func->old_addr not having expected values,
we'd rather bail out immediately from klp_disable_func().

This can't really happen with the current codebase, but fix this
anyway in the sake of robustness.

[jkosina@suse.com: reworded the changelog a bit]
Signed-off-by: NMinfei Huang <mnfhuang@gmail.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.com>

The list of loaded modules is walked through in
module_kallsyms_on_each_symbol (called by kallsyms_on_each_symbol). The
module_mutex lock should be acquired to prevent potential corruptions
in the list.

This was uncovered with new lockdep asserts in module code introduced by
the commit 0be964be ("module: Sanitize RCU usage and locking") in
recent next- trees.
Signed-off-by: NMiroslav Benes <mbenes@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

module_init() function should be marked __init.

[jkosina@suse.cz: remove overly verbose changelog]
Signed-off-by: NMinfei Huang <mnfhuang@gmail.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

klp_for_each_object and klp_for_each_func are now used all over the
code. One need not think what is the proper condition to check in the
for loop now.
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Make kobj variable (of type struct kobject) statically allocated in
klp_object structure. It will allow us to move in the func-object-patch
hierarchy through kobject links.

The only reason to have it dynamic was to not have empty release
callback in the code. However we have empty callbacks for function and
patch in the code now, so it is no longer valid and the advantage of
static allocation is clear.
Signed-off-by: NMiroslav Benes <mbenes@suse.cz>
Signed-off-by: NJiri Slaby <jslaby@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

The previous patches can be applied, once the corresponding module is
loaded. In general, the patch will do relocation (if necessary) and
obtain/verify function address before we start to enable patch.

There are three different situations in which the coming module notifier
can fail:

1) relocations are not applied for some reason. In this case kallsyms
for module symbol is not called at all. The patch is not applied to the
module. If the user disable and enable patch again, there is possible
bug in klp_enable_func. If the user specified func->old_addr for some
function in the module (and he shouldn't do that, but nevertheless) our
warning would not catch it, ftrace will reject to register the handler
because of wrong address or will register the handler for wrong address.

2) relocations are applied successfully, but kallsyms lookup fails. In
this case func->old_addr can be correct for all previous lookups, 0 for
current failed one, and "unspecified" for the rest. If we undergo the
same scenario as in 1, the behaviour differs for three cases, but the
patch is not enabled anyway.

3) the object is initialized, but klp_enable_object fails in the
notifier due to possible ftrace error. Since it is improbable that
ftrace would heal itself in the future, we would get those errors
everytime the patch is enabled.

In order to fix above situations, we can make obj->mod to NULL, if the
coming modified notifier fails.
Signed-off-by: NMinfei Huang <mnfhuang@gmail.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NMiroslav Benes <mbenes@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

klp_initialized() should return bool but is actually returning
struct kobject * - convert it to a boolean explicitly.
Signed-off-by: NNicholas Mc Guire <hofrat@osadl.org>
Reviewed-by: Jiri Slaby <jslaby@suse.cz
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

We give up old_addr hint from the coming patch module in cases when kernel load
base has been randomized (as in such case, the coming module has no idea about
the exact randomization offset).

We are currently too pessimistic, and give up immediately as soon as
CONFIG_RANDOMIZE_BASE is set; this doesn't however directly imply that the
load base has actually been randomized. There are config options that
disable kASLR (such as hibernation), user could have disabled kaslr on
kernel command-line, etc.

The loader propagates the information whether kernel has been randomized
through bootparams. This allows us to have the condition more accurate.

On top of that, it seems unnecessary to give up old_addr hints even if
randomization is active. The relocation offset can be computed using
kaslr_ofsset(), and therefore old_addr can be adjusted accordingly.
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

There is a notifier that handles live patches for coming and going modules.
It takes klp_mutex lock to avoid races with coming and going patches but
it does not keep the lock all the time. Therefore the following races are
possible:

  1. The notifier is called sometime in STATE_MODULE_COMING. The module
     is visible by find_module() in this state all the time. It means that
     new patch can be registered and enabled even before the notifier is
     called. It might create wrong order of stacked patches, see below
     for an example.

   2. New patch could still see the module in the GOING state even after
      the notifier has been called. It will try to initialize the related
      object structures but the module could disappear at any time. There
      will stay mess in the structures. It might even cause an invalid
      memory access.

This patch solves the problem by adding a boolean variable into struct module.
The value is true after the coming and before the going handler is called.
New patches need to be applied when the value is true and they need to ignore
the module when the value is false.

Note that we need to know state of all modules on the system. The races are
related to new patches. Therefore we do not know what modules will get
patched.

Also note that we could not simply ignore going modules. The code from the
module could be called even in the GOING state until mod->exit() finishes.
If we start supporting patches with semantic changes between function
calls, we need to apply new patches to any still usable code.
See below for an example.

Finally note that the patch solves only the situation when a new patch is
registered. There are no such problems when the patch is being removed.
It does not matter who disable the patch first, whether the normal
disable_patch() or the module notifier. There is nothing to do
once the patch is disabled.

Alternative solutions:
======================

+ reject new patches when a patched module is coming or going; this is ugly

+ wait with adding new patch until the module leaves the COMING and GOING
  states; this might be dangerous and complicated; we would need to release
  kgr_lock in the middle of the patch registration to avoid a deadlock
  with the coming and going handlers; also we might need a waitqueue for
  each module which seems to be even bigger overhead than the boolean

+ stop modules from entering COMING and GOING states; wait until modules
  leave these states when they are already there; looks complicated; we would
  need to ignore the module that asked to stop the others to avoid a deadlock;
  also it is unclear what to do when two modules asked to stop others and
  both are in COMING state (situation when two new patches are applied)

+ always register/enable new patches and fix up the potential mess (registered
  patches order) in klp_module_init(); this is nasty and prone to regressions
  in the future development

+ add another MODULE_STATE where the kallsyms are visible but the module is not
  used yet; this looks too complex; the module states are checked on "many"
  locations

Example of patch stacking breakage:
===================================

The notifier could _not_ _simply_ ignore already initialized module objects.
For example, let's have three patches (P1, P2, P3) for functions a() and b()
where a() is from vmcore and b() is from a module M. Something like:

	a()	b()
P1	a1()	b1()
P2	a2()	b2()
P3	a3()	b3(3)

If you load the module M after all patches are registered and enabled.
The ftrace ops for function a() and b() has listed the functions in this
order:

	ops_a->func_stack -> list(a3,a2,a1)
	ops_b->func_stack -> list(b3,b2,b1)

, so the pointer to b3() is the first and will be used.

Then you might have the following scenario. Let's start with state when patches
P1 and P2 are registered and enabled but the module M is not loaded. Then ftrace
ops for b() does not exist. Then we get into the following race:

CPU0					CPU1

load_module(M)

  complete_formation()

  mod->state = MODULE_STATE_COMING;
  mutex_unlock(&module_mutex);

					klp_register_patch(P3);
					klp_enable_patch(P3);

					# STATE 1

  klp_module_notify(M)
    klp_module_notify_coming(P1);
    klp_module_notify_coming(P2);
    klp_module_notify_coming(P3);

					# STATE 2

The ftrace ops for a() and b() then looks:

  STATE1:

	ops_a->func_stack -> list(a3,a2,a1);
	ops_b->func_stack -> list(b3);

  STATE2:
	ops_a->func_stack -> list(a3,a2,a1);
	ops_b->func_stack -> list(b2,b1,b3);

therefore, b2() is used for the module but a3() is used for vmcore
because they were the last added.

Example of the race with going modules:
=======================================

CPU0					CPU1

delete_module()  #SYSCALL

   try_stop_module()
     mod->state = MODULE_STATE_GOING;

   mutex_unlock(&module_mutex);

					klp_register_patch()
					klp_enable_patch()

					#save place to switch universe

					b()     # from module that is going
					  a()   # from core (patched)

   mod->exit();

Note that the function b() can be called until we call mod->exit().

If we do not apply patch against b() because it is in MODULE_STATE_GOING,
it will call patched a() with modified semantic and things might get wrong.

[jpoimboe@redhat.com: use one boolean instead of two]
Signed-off-by: NPetr Mladek <pmladek@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

klp_find_object_module() is called from both the klp register and enable
paths.  Only the call from the register path is necessary because the
module notifier will let us know if the patched module gets loaded or
unloaded.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NPetr Mladek <pmladek@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

While one must hold RCU-sched (aka. preempt_disable) for find_symbol()
one must equally hold it over the use of the object returned.

The moment you release the RCU-sched read lock, the object can be dead
and gone.

[jkosina@suse.cz: change subject line to be aligned with other patches]
Cc: Seth Jennings <sjenning@redhat.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Petr Mladek <pmladek@suse.cz>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: NMasami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Acked-by: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

func->new_func has been accessed after rcu_read_unlock() in klp_ftrace_handler()
and therefore the access was not protected.
Signed-off-by: NPetr Mladek <pmladek@suse.cz>
Acked-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

If registering the function with ftrace has previously succeeded,
unregistering will almost never fail.  Even if it does, it's not a fatal
error.  We can still carry on and disable the klp_func from being used
by removing it from the klp_ops func stack.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NMiroslav Benes <mbenes@suse.cz>
Reviewed-by: NPetr Mladek <pmladek@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

kobject_init_and_add() takes expects format string for a name, so we
better provide it in order to avoid infoleaks if modules craft their
mod->name in a special way.
Reported-by: NFengguang Wu <fengguang.wu@intel.com>
Reported-by: NKees Cook <keescook@chromium.org>
Acked-by: NSeth Jennings <sjenning@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Fix a potentially uninitialized return value in klp_enable_func().
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NMiroslav Benes <mbenes@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Add support for patching a function multiple times.  If multiple patches
affect a function, the function in the most recently enabled patch
"wins".  This enables a cumulative patch upgrade path, where each patch
is a superset of previous patches.

This requires restructuring the data a little bit.  With the current
design, where each klp_func struct has its own ftrace_ops, we'd have to
unregister the old ops and then register the new ops, because
FTRACE_OPS_FL_IPMODIFY prevents us from having two ops registered for
the same function at the same time.  That would leave a regression
window where the function isn't patched at all (not good for a patch
upgrade path).

This patch replaces the per-klp_func ftrace_ops with a global klp_ops
list, with one ftrace_ops per original function.  A single ftrace_ops is
shared between all klp_funcs which have the same old_addr.  This allows
the switch between function versions to happen instantaneously by
updating the klp_ops struct's func_stack list.  The winner is the
klp_func at the top of the func_stack (front of the list).

[ jkosina@suse.cz: turn WARN_ON() into WARN_ON_ONCE() in ftrace handler to
  avoid storm in pathological cases ]
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

Only allow the topmost patch on the stack to be enabled or disabled, so
that patches can't be removed or added in an arbitrary order.
Suggested-by: NJiri Kosina <jkosina@suse.cz>
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: NJiri Slaby <jslaby@suse.cz>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>

When applying multiple patches to a module, if the module is loaded
after the patches are loaded, the patches are applied in reverse order:

  $ insmod patch1.ko
  [   43.172992] livepatch: enabling patch 'patch1'

  $ insmod patch2.ko
  [   46.571563] livepatch: enabling patch 'patch2'

  $ modprobe nfsd
  [   52.888922] livepatch: applying patch 'patch2' to loading module 'nfsd'
  [   52.899847] livepatch: applying patch 'patch1' to loading module 'nfsd'

Fix the loading order by storing the klp_patches list in queue order.
Signed-off-by: NJosh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>