21 Aug, 2018
1 commit
23 Jul, 2018
1 commit
-
livepatch module author can pass module name/old function name with more
than the defined character limit. With obj->name length greater than
MODULE_NAME_LEN, the livepatch module gets loaded but waits forever on
the module specified by obj->name to be loaded. It also populates a /sys
directory with an untruncated object name.In the case of funcs->old_name length greater then KSYM_NAME_LEN, it
would not match against any of the symbol table entries. Instead loop
through the symbol table comparing them against a nonexisting function,
which can be avoided.The same issues apply, to misspelled/incorrect names. At least gatekeep
the modules with over the limit string length, by checking for their
length during livepatch module registration.Cc: stable@vger.kernel.org
Signed-off-by: Kamalesh Babulal
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina
16 Jul, 2018
1 commit
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Support for immediate flag was removed by commit d0807da78e11
("livepatch: Remove immediate feature"). We bail out during
patch registration for architectures, those don't support
reliable stack trace. Remove the check in klp_try_switch_task(),
as its not required.Signed-off-by: Kamalesh Babulal
Reviewed-by: Petr Mladek
Acked-by: Miroslav Benes
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina
17 Apr, 2018
2 commits
-
We might need to do some actions before the shadow variable is freed.
For example, we might need to remove it from a list or free some data
that it points to.This is already possible now. The user can get the shadow variable
by klp_shadow_get(), do the necessary actions, and then call
klp_shadow_free().This patch allows to do it a more elegant way. The user could implement
the needed actions in a callback that is passed to klp_shadow_free()
as a parameter. The callback usually does reverse operations to
the constructor callback that can be called by klp_shadow_*alloc().It is especially useful for klp_shadow_free_all(). There we need to do
these extra actions for each found shadow variable with the given ID.Note that the memory used by the shadow variable itself is still released
later by rcu callback. It is needed to protect internal structures that
keep all shadow variables. But the destructor is called immediately.
The shadow variable must not be access anyway after klp_shadow_free()
is called. The user is responsible to protect this any suitable way.Be aware that the destructor is called under klp_shadow_lock. It is
the same as for the contructor in klp_shadow_alloc().Signed-off-by: Petr Mladek
Acked-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina -
The existing API allows to pass a sample data to initialize the shadow
data. It works well when the data are position independent. But it fails
miserably when we need to set a pointer to the shadow structure itself.Unfortunately, we might need to initialize the pointer surprisingly
often because of struct list_head. It is even worse because the list
might be hidden in other common structures, for example, struct mutex,
struct wait_queue_head.For example, this was needed to fix races in ALSA sequencer. It required
to add mutex into struct snd_seq_client. See commit b3defb791b26ea06
("ALSA: seq: Make ioctls race-free") and commit d15d662e89fc667b9
("ALSA: seq: Fix racy pool initializations")This patch makes the API more safe. A custom constructor function and data
are passed to klp_shadow_*alloc() functions instead of the sample data.Note that ctor_data are no longer a template for shadow->data. It might
point to any data that might be necessary when the constructor is called.Also note that the constructor is called under klp_shadow_lock. It is
an internal spin_lock that synchronizes alloc() vs. get() operations,
see klp_shadow_get_or_alloc(). On one hand, this adds a risk of ABBA
deadlocks. On the other hand, it allows to do some operations safely.
For example, we could add the new structure into an existing list.
This must be done only once when the structure is allocated.Reported-by: Nicolai Stange
Signed-off-by: Petr Mladek
Acked-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina
31 Jan, 2018
1 commit
-
Pull 'immediate' feature removal from Miroslav Benes.
12 Jan, 2018
1 commit
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klp_send_signals() and klp_force_transition() do not acquire klp_mutex,
because it seemed to be superfluous. A potential race in
klp_send_signals() was harmless and there was nothing in
klp_force_transition() which needed to be synchronized. That changed
with the addition of klp_forced variable during the review process.There is a small window now, when klp_complete_transition() does not see
klp_forced set to true while all tasks have been already transitioned to
the target state. module_put() is called and the module can be removed.Acquire klp_mutex in sysfs callback to prevent it. Do the same for the
signal sending just to be sure. There is no real downside to that.Fixes: c99a2be790b07 ("livepatch: force transition to finish")
Fixes: 43347d56c8d9d ("livepatch: send a fake signal to all blocking tasks")
Reported-by: Jason Baron
Signed-off-by: Miroslav Benes
Reviewed-by: Petr Mladek
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina
11 Jan, 2018
1 commit
-
Immediate flag has been used to disable per-task consistency and patch
all tasks immediately. It could be useful if the patch doesn't change any
function or data semantics.However, it causes problems on its own. The consistency problem is
currently broken with respect to immediate patches.func a
patches 1i
2i
3When the patch 3 is applied, only 2i function is checked (by stack
checking facility). There might be a task sleeping in 1i though. Such
task is migrated to 3, because we do not check 1i in
klp_check_stack_func() at all.Coming atomic replace feature would be easier to implement and more
reliable without immediate.Thus, remove immediate feature completely and save us from the problems.
Note that force feature has the similar problem. However it is
considered as a last resort. If used, administrator should not apply any
new live patches and should plan for reboot into an updated kernel.The architectures would now need to provide HAVE_RELIABLE_STACKTRACE to
fully support livepatch.Signed-off-by: Miroslav Benes
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina
07 Dec, 2017
1 commit
-
If a task sleeps in a set of patched functions uninterruptedly, it could
block the whole transition indefinitely. Thus it may be useful to clear
its TIF_PATCH_PENDING to allow the process to finish.Admin can do that now by writing to force sysfs attribute in livepatch
sysfs directory. TIF_PATCH_PENDING is then cleared for all tasks and the
transition can finish successfully.Important note! Administrator should not use this feature without a
clearance from a patch distributor. It must be checked that by doing so
the consistency model guarantees are not violated. Removal (rmmod) of
patch modules is permanently disabled when the feature is used. It
cannot be guaranteed there is no task sleeping in such module.Signed-off-by: Miroslav Benes
Acked-by: Josh Poimboeuf
Reviewed-by: Petr Mladek
Signed-off-by: Jiri Kosina
05 Dec, 2017
1 commit
-
Live patching consistency model is of LEAVE_PATCHED_SET and
SWITCH_THREAD. This means that all tasks in the system have to be marked
one by one as safe to call a new patched function. Safe means when a
task is not (sleeping) in a set of patched functions. That is, no
patched function is on the task's stack. Another clearly safe place is
the boundary between kernel and userspace. The patching waits for all
tasks to get outside of the patched set or to cross the boundary. The
transition is completed afterwards.The problem is that a task can block the transition for quite a long
time, if not forever. It could sleep in a set of patched functions, for
example. Luckily we can force the task to leave the set by sending it a
fake signal, that is a signal with no data in signal pending structures
(no handler, no sign of proper signal delivered). Suspend/freezer use
this to freeze the tasks as well. The task gets TIF_SIGPENDING set and
is woken up (if it has been sleeping in the kernel before) or kicked by
rescheduling IPI (if it was running on other CPU). This causes the task
to go to kernel/userspace boundary where the signal would be handled and
the task would be marked as safe in terms of live patching.There are tasks which are not affected by this technique though. The
fake signal is not sent to kthreads. They should be handled differently.
They can be woken up so they leave the patched set and their
TIF_PATCH_PENDING can be cleared thanks to stack checking.For the sake of completeness, if the task is in TASK_RUNNING state but
not currently running on some CPU it doesn't get the IPI, but it would
eventually handle the signal anyway. Second, if the task runs in the
kernel (in TASK_RUNNING state) it gets the IPI, but the signal is not
handled on return from the interrupt. It would be handled on return to
the userspace in the future when the fake signal is sent again. Stack
checking deals with these cases in a better way.If the task was sleeping in a syscall it would be woken by our fake
signal, it would check if TIF_SIGPENDING is set (by calling
signal_pending() predicate) and return ERESTART* or EINTR. Syscalls with
ERESTART* return values are restarted in case of the fake signal (see
do_signal()). EINTR is propagated back to the userspace program. This
could disturb the program, but...* each process dealing with signals should react accordingly to EINTR
return values.
* syscalls returning EINTR happen to be quite common situation in the
system even if no fake signal is sent.
* freezer sends the fake signal and does not deal with EINTR anyhow.
Thus EINTR values are returned when the system is resumed.The very safe marking is done in architectures' "entry" on syscall and
interrupt/exception exit paths, and in a stack checking functions of
livepatch. TIF_PATCH_PENDING is cleared and the next
recalc_sigpending() drops TIF_SIGPENDING. In connection with this, also
call klp_update_patch_state() before do_signal(), so that
recalc_sigpending() in dequeue_signal() can clear TIF_PATCH_PENDING
immediately and thus prevent a double call of do_signal().Note that the fake signal is not sent to stopped/traced tasks. Such task
prevents the patching to finish till it continues again (is not traced
anymore).Last, sending the fake signal is not automatic. It is done only when
admin requests it by writing 1 to signal sysfs attribute in livepatch
sysfs directory.Signed-off-by: Miroslav Benes
Cc: Oleg Nesterov
Cc: Michael Ellerman
Cc: Thomas Gleixner
Cc: Ingo Molnar
Cc: "H. Peter Anvin"
Cc: Andy Lutomirski
Cc: linuxppc-dev@lists.ozlabs.org
Cc: x86@kernel.org
Acked-by: Michael Ellerman (powerpc)
Signed-off-by: Jiri Kosina
16 Nov, 2017
1 commit
-
Pull livepatching updates from Jiri Kosina:
- shadow variables support, allowing livepatches to associate new
"shadow" fields to existing data structures, from Joe Lawrence- pre/post patch callbacks API, allowing livepatch writers to register
callbacks to be called before and after patch application, from Joe
Lawrence* 'for-linus' of ssh://gitolite.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
livepatch: __klp_disable_patch() should never be called for disabled patches
livepatch: Correctly call klp_post_unpatch_callback() in error paths
livepatch: add transition notices
livepatch: move transition "complete" notice into klp_complete_transition()
livepatch: add (un)patch callbacks
livepatch: Small shadow variable documentation fixes
livepatch: __klp_shadow_get_or_alloc() is local to shadow.c
livepatch: introduce shadow variable API
15 Nov, 2017
2 commits
-
This pulls in an infrastructure/API that allows livepatch writers to
register pre-patch and post-patch callbacks that allow for running a
glue code necessary for finalizing the patching if necessary.Conflicts:
kernel/livepatch/core.c
- trivial conflict by adding a callback call into
module going notifier vs. moving that code block
to klp_cleanup_module_patches_limited()Signed-off-by: Jiri Kosina
-
Shadow variables allow callers to associate new shadow fields to existing data
structures. This is intended to be used by livepatch modules seeking to
emulate additions to data structure definitions.
02 Nov, 2017
1 commit
-
Many source files in the tree are missing licensing information, which
makes it harder for compliance tools to determine the correct license.By default all files without license information are under the default
license of the kernel, which is GPL version 2.Update the files which contain no license information with the 'GPL-2.0'
SPDX license identifier. The SPDX identifier is a legally binding
shorthand, which can be used instead of the full boiler plate text.This patch is based on work done by Thomas Gleixner and Kate Stewart and
Philippe Ombredanne.How this work was done:
Patches were generated and checked against linux-4.14-rc6 for a subset of
the use cases:
- file had no licensing information it it.
- file was a */uapi/* one with no licensing information in it,
- file was a */uapi/* one with existing licensing information,Further patches will be generated in subsequent months to fix up cases
where non-standard license headers were used, and references to license
had to be inferred by heuristics based on keywords.The analysis to determine which SPDX License Identifier to be applied to
a file was done in a spreadsheet of side by side results from of the
output of two independent scanners (ScanCode & Windriver) producing SPDX
tag:value files created by Philippe Ombredanne. Philippe prepared the
base worksheet, and did an initial spot review of a few 1000 files.The 4.13 kernel was the starting point of the analysis with 60,537 files
assessed. Kate Stewart did a file by file comparison of the scanner
results in the spreadsheet to determine which SPDX license identifier(s)
to be applied to the file. She confirmed any determination that was not
immediately clear with lawyers working with the Linux Foundation.Criteria used to select files for SPDX license identifier tagging was:
- Files considered eligible had to be source code files.
- Make and config files were included as candidates if they contained >5
lines of source
- File already had some variant of a license header in it (even if
Reviewed-by: Philippe Ombredanne
Reviewed-by: Thomas Gleixner
Signed-off-by: Greg Kroah-Hartman
26 Oct, 2017
2 commits
-
__klp_disable_patch() should never be called when the patch is not
enabled. Let's add the same warning that we have in __klp_enable_patch().This allows to remove the check when calling klp_pre_unpatch_callback().
It was strange anyway because it repeatedly checked per-patch flag
for each patched object.Signed-off-by: Petr Mladek
Acked-by: Joe Lawrence
Signed-off-by: Jiri Kosina -
The post_unpatch_enabled flag in struct klp_callbacks is set when a
pre-patch callback successfully executes, indicating that we need to
call a corresponding post-unpatch callback when the patch is reverted.
This is true for ordinary patch disable as well as the error paths of
klp_patch_object() callers.As currently coded, we inadvertently execute the post-patch callback
twice in klp_module_coming() when klp_patch_object() fails:- We explicitly call klp_post_unpatch_callback() for the failed object
- We call it again for the same object (and all the others) via
klp_cleanup_module_patches_limited()We should clear the flag in klp_post_unpatch_callback() to make
sure that the callback is not called twice. It makes the API
more safe.(We could have removed the callback from the former error path as it
would be covered by the latter call, but I think that is is cleaner to
clear the post_unpatch_enabled after its invoked. For example, someone
might later decide to call the callback only when obj->patched flag is
set.)There is another mistake in the error path of klp_coming_module() in
which it skips the post-unpatch callback for the klp_transition_patch.
However, the pre-patch callback was called even for this patch, so be
sure to make the corresponding callbacks for all patches.Finally, I used this opportunity to make klp_pre_patch_callback() more
readable.[jkosina@suse.cz: incorporate changelog wording changes proposed by Joe Lawrence]
Signed-off-by: Petr Mladek
Acked-by: Joe Lawrence
Signed-off-by: Jiri Kosina
19 Oct, 2017
3 commits
-
Log a few kernel debug messages at the beginning of the following livepatch
transition functions:klp_complete_transition()
klp_cancel_transition()
klp_init_transition()
klp_reverse_transition()Also update the log notice message in klp_start_transition() for similar
verbiage as the above messages.Suggested-by: Josh Poimboeuf
Signed-off-by: Joe Lawrence
Acked-by: Miroslav Benes
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina -
klp_complete_transition() performs a bit of housework before a
transition to KLP_PATCHED or KLP_UNPATCHED is actually completed
(including post-(un)patch callbacks). To be consistent, move the
transition "complete" kernel log notice out of
klp_try_complete_transition() and into klp_complete_transition().Suggested-by: Josh Poimboeuf
Acked-by: Josh Poimboeuf
Signed-off-by: Joe Lawrence
Acked-by: Miroslav Benes
Reviewed-by: Petr Mladek
Signed-off-by: Jiri Kosina -
Provide livepatch modules a klp_object (un)patching notification
mechanism. Pre and post-(un)patch callbacks allow livepatch modules to
setup or synchronize changes that would be difficult to support in only
patched-or-unpatched code contexts.Callbacks can be registered for target module or vmlinux klp_objects,
but each implementation is klp_object specific.- Pre-(un)patch callbacks run before any (un)patching transition
starts.- Post-(un)patch callbacks run once an object has been (un)patched and
the klp_patch fully transitioned to its target state.Example use cases include modification of global data and registration
of newly available services/handlers.See Documentation/livepatch/callbacks.txt for details and
samples/livepatch/ for examples.Signed-off-by: Joe Lawrence
Acked-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina
11 Oct, 2017
1 commit
-
When an incoming module is considered for livepatching by
klp_module_coming(), it iterates over multiple patches and multiple
kernel objects in this order:list_for_each_entry(patch, &klp_patches, list) {
klp_for_each_object(patch, obj) {which means that if one of the kernel objects fails to patch,
klp_module_coming()'s error path needs to unpatch and cleanup any kernel
objects that were already patched by a previous patch.Reported-by: Miroslav Benes
Suggested-by: Petr Mladek
Signed-off-by: Joe Lawrence
Acked-by: Josh Poimboeuf
Reviewed-by: Petr Mladek
Signed-off-by: Jiri Kosina
16 Sep, 2017
1 commit
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... therefore make it static.
Fixes: 439e7271dc2 ("livepatch: introduce shadow variable API")
Acked-by: Joe Lawrence
Signed-off-by: Jiri Kosina
15 Sep, 2017
1 commit
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Add exported API for livepatch modules:
klp_shadow_get()
klp_shadow_alloc()
klp_shadow_get_or_alloc()
klp_shadow_free()
klp_shadow_free_all()that implement "shadow" variables, which allow callers to associate new
shadow fields to existing data structures. This is intended to be used
by livepatch modules seeking to emulate additions to data structure
definitions.See Documentation/livepatch/shadow-vars.txt for a summary of the new
shadow variable API, including a few common use cases.See samples/livepatch/livepatch-shadow-* for example modules that
demonstrate shadow variables.[jkosina@suse.cz: fix __klp_shadow_get_or_alloc() comment as spotted by
Josh]
Signed-off-by: Joe Lawrence
Acked-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina
20 Jun, 2017
1 commit
-
rcu_read_(un)lock(), list_*_rcu(), and synchronize_rcu() are used for a secure
access and manipulation of the list of patches that modify the same function.
In particular, it is the variable func_stack that is accessible from the ftrace
handler via struct ftrace_ops and klp_ops.Of course, it synchronizes also some states of the patch on the top of the
stack, e.g. func->transition in klp_ftrace_handler.At the same time, this mechanism guards also the manipulation of
task->patch_state. It is modified according to the state of the transition and
the state of the process.Now, all this works well as long as RCU works well. Sadly livepatching might
get into some corner cases when this is not true. For example, RCU is not
watching when rcu_read_lock() is taken in idle threads. It is because they
might sleep and prevent reaching the grace period for too long.There are ways how to make RCU watching even in idle threads, see
rcu_irq_enter(). But there is a small location inside RCU infrastructure when
even this does not work.This small problematic location can be detected either before calling
rcu_irq_enter() by rcu_irq_enter_disabled() or later by rcu_is_watching().
Sadly, there is no safe way how to handle it. Once we detect that RCU was not
watching, we might see inconsistent state of the function stack and the related
variables in klp_ftrace_handler(). Then we could do a wrong decision, use an
incompatible implementation of the function and break the consistency of the
system. We could warn but we could not avoid the damage.Fortunately, ftrace has similar problems and they seem to be solved well there.
It uses a heavy weight implementation of some RCU operations. In particular, it
replaces:+ rcu_read_lock() with preempt_disable_notrace()
+ rcu_read_unlock() with preempt_enable_notrace()
+ synchronize_rcu() with schedule_on_each_cpu(sync_work)My understanding is that this is RCU implementation from a stone age. It meets
the core RCU requirements but it is rather ineffective. Especially, it does not
allow to batch or speed up the synchronize calls.On the other hand, it is very trivial. It allows to safely trace and/or
livepatch even the RCU core infrastructure. And the effectiveness is a not a
big issue because using ftrace or livepatches on productive systems is a rare
operation. The safety is much more important than a negligible extra load.Note that the alternative implementation follows the RCU principles. Therefore,
we could and actually must use list_*_rcu() variants when manipulating the
func_stack. These functions allow to access the pointers in the right
order and with the right barriers. But they do not use any other
information that would be set only by rcu_read_lock().Also note that there are actually two problems solved in ftrace:
First, it cares about the consistency of RCU read sections. It is being solved
the way as described and used in this patch.Second, ftrace needs to make sure that nobody is inside the dynamic trampoline
when it is being freed. For this, it also calls synchronize_rcu_tasks() in
preemptive kernel in ftrace_shutdown().Livepatch has similar problem but it is solved by ftrace for free.
klp_ftrace_handler() is a good guy and never sleeps. In addition, it is
registered with FTRACE_OPS_FL_DYNAMIC. It causes that
unregister_ftrace_function() calls:* schedule_on_each_cpu(ftrace_sync) - always
* synchronize_rcu_tasks() - in preemptive kernelThe effect is that nobody is neither inside the dynamic trampoline nor inside
the ftrace handler after unregister_ftrace_function() returns.[jkosina@suse.cz: reformat changelog, fix comment]
Signed-off-by: Petr Mladek
Acked-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina
27 May, 2017
1 commit
-
If TRIM_UNUSED_KSYMS is enabled, all unneeded exported symbols are made
unexported. Two-pass build of the kernel is done to find out which
symbols are needed based on a configuration. This effectively
complicates things for out-of-tree modules.Livepatch exports functions to (un)register and enable/disable a live
patch. The only in-tree module which uses these functions is a sample in
samples/livepatch/. If the sample is disabled, the functions are
trimmed and out-of-tree live patches cannot be built.Note that live patches are intended to be built out-of-tree.
Suggested-by: Michal Marek
Acked-by: Josh Poimboeuf
Acked-by: Jessica Yu
Signed-off-by: Miroslav Benes
Signed-off-by: Jiri Kosina
02 May, 2017
1 commit
17 Apr, 2017
1 commit
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Add missing newlines to some pr_err() strings.
Signed-off-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Acked-by: Jessica Yu
Signed-off-by: Jiri Kosina
12 Apr, 2017
1 commit
-
klp_init_transition() does not set func->transition for immediate patches.
Then klp_ftrace_handler() could use the new code immediately. As a result,
it is not safe to put the livepatch module in klp_cancel_transition().This patch reverts most of the last minute changes klp_cancel_transition().
It keeps the warning about a misuse because it still makes sense.Fixes: 3ec24776bfd0 ("livepatch: allow removal of a disabled patch")
Signed-off-by: Petr Mladek
Acked-by: Miroslav Benes
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina
30 Mar, 2017
1 commit
-
It's reported that the time of insmoding a klp.ko for one of our
out-tree modules is too long.~ time sudo insmod klp.ko
real 0m23.799s
user 0m0.036s
sys 0m21.256sThen we found the reason: our out-tree module used a lot of static local
variables, so klp.ko has a lot of relocation records which reference the
module. Then for each such entry klp_find_object_symbol() is called to
resolve it, but this function uses the interface kallsyms_on_each_symbol()
even for finding module symbols, so will waste a lot of time on walking
through vmlinux kallsyms table many times.This patch changes it to use module_kallsyms_on_each_symbol() for modules
symbols. After we apply this patch, the sys time reduced dramatically.~ time sudo insmod klp.ko
real 0m1.007s
user 0m0.032s
sys 0m0.924sSigned-off-by: Zhou Chengming
Acked-by: Josh Poimboeuf
Acked-by: Jessica Yu
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina
08 Mar, 2017
9 commits
-
klp_mutex is shared between core.c and transition.c, and as such would
rather be properly located in a header so that we don't have to play
'extern' games from .c sources.This also silences sparse warning (wrongly) suggesting that klp_mutex
should be defined static.Acked-by: Miroslav Benes
Acked-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina -
Currently we do not allow patch module to unload since there is no
method to determine if a task is still running in the patched code.The consistency model gives us the way because when the unpatching
finishes we know that all tasks were marked as safe to call an original
function. Thus every new call to the function calls the original code
and at the same time no task can be somewhere in the patched code,
because it had to leave that code to be marked as safe.We can safely let the patch module go after that.
Completion is used for synchronization between module removal and sysfs
infrastructure in a similar way to commit 942e443127e9 ("module: Fix
mod->mkobj.kobj potentially freed too early").Note that we still do not allow the removal for immediate model, that is
no consistency model. The module refcount may increase in this case if
somebody disables and enables the patch several times. This should not
cause any harm.With this change a call to try_module_get() is moved to
__klp_enable_patch from klp_register_patch to make module reference
counting symmetric (module_put() is in a patch disable path) and to
allow to take a new reference to a disabled module when being enabled.Finally, we need to be very careful about possible races between
klp_unregister_patch(), kobject_put() functions and operations
on the related sysfs files.kobject_put(&patch->kobj) must be called without klp_mutex. Otherwise,
it might be blocked by enabled_store() that needs the mutex as well.
In addition, enabled_store() must check if the patch was not
unregisted in the meantime.There is no need to do the same for other kobject_put() callsites
at the moment. Their sysfs operations neither take the lock nor
they access any data that might be freed in the meantime.There was an attempt to use kobjects the right way and prevent these
races by design. But it made the patch definition more complicated
and opened another can of worms. See
https://lkml.kernel.org/r/1464018848-4303-1-git-send-email-pmladek@suse.com[Thanks to Petr Mladek for improving the commit message.]
Signed-off-by: Miroslav Benes
Signed-off-by: Josh Poimboeuf
Reviewed-by: Petr Mladek
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina -
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//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//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.cz
Signed-off-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Acked-by: Ingo Molnar # for the scheduler changes
Signed-off-by: Jiri Kosina -
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: Josh Poimboeuf
Acked-by: Miroslav Benes
Reviewed-by: Petr Mladek
Reviewed-by: Kamalesh Babulal
Signed-off-by: Jiri Kosina -
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: Petr Mladek
Signed-off-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Reviewed-by: Petr Mladek
Signed-off-by: Jiri Kosina -
Move functions related to the actual patching of functions and objects
into a new patch.c file.Signed-off-by: Josh Poimboeuf
Acked-by: Miroslav Benes
Reviewed-by: Petr Mladek
Reviewed-by: Kamalesh Babulal
Signed-off-by: Jiri Kosina -
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: Josh Poimboeuf
Acked-by: Miroslav Benes
Reviewed-by: Petr Mladek
Reviewed-by: Kamalesh Babulal
Signed-off-by: Jiri Kosina -
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: Josh Poimboeuf
Acked-by: Miroslav Benes
Reviewed-by: Petr Mladek
Reviewed-by: Kamalesh Babulal
Signed-off-by: Jiri Kosina -
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: Josh Poimboeuf
Reviewed-by: Petr Mladek
Signed-off-by: Jiri Kosina
26 Aug, 2016
1 commit
-
There's no reliable way to determine which module tainted the kernel
with TAINT_LIVEPATCH. For example, /sys/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: Chunyu Hu
Reviewed-by: Petr Mladek
Acked-by: Miroslav Benes
Acked-by: Jessica Yu
Acked-by: Rusty Russell
Signed-off-by: Josh Poimboeuf
Signed-off-by: Jiri Kosina
19 Aug, 2016
1 commit
-
Introduce arch_klp_init_object_loaded() to complete any additional
arch-specific tasks during patching. Architecture code may override this
function.Signed-off-by: Jessica Yu
Reviewed-by: Petr Mladek
Acked-by: Miroslav Benes
Signed-off-by: Jiri Kosina
04 Aug, 2016
1 commit
-
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: Jessica Yu
Acked-by: Kees Cook
Signed-off-by: Rusty Russell