user/sven/linux.git/kernel/livepatch, branch v4.18.8

livepatch: Validate module/old func name length

2018-09-09T08:32:35Z

commit 6e9df95b76cad18f7b217bdad7bb8a26d63b8c47 upstream. 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 Signed-off-by: Greg Kroah-Hartman

livepatch: Allow to call a custom callback when freeing shadow variables

2018-04-17T11:42:48Z

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

livepatch: Initialize shadow variables safely by a custom callback

2018-04-17T11:42:48Z

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

Merge branch 'for-4.16/remove-immediate' into for-linus

2018-01-31T15:36:38Z

Pull 'immediate' feature removal from Miroslav Benes.

livepatch: add locking to force and signal functions

2018-01-11T16:36:07Z

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

livepatch: Remove immediate feature

2018-01-11T09:58:03Z

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 3 When 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

livepatch: force transition to finish

2017-12-07T12:21:35Z

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

livepatch: send a fake signal to all blocking tasks

2017-12-04T21:34:57Z

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

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

2017-11-15T18:21:58Z

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

Merge branch 'for-4.15/callbacks' into for-linus

2017-11-15T09:54:27Z

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