Livepatch sends a fake signal to all remaining blocking tasks of a
running transition after a set period of time. It uses TIF_SIGPENDING
flag for the purpose. Commit 12db8b6900 ("entry: Add support for
TIF_NOTIFY_SIGNAL") added a generic infrastructure to achieve the same.
Replace our bespoke solution with the generic one.
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Pull livepatching updates from Jiri Kosina:
- stacktrace handling improvements from Miroslav benes
- debug output improvements from Petr Mladek
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/livepatching/livepatching:
livepatch: Remove duplicate warning about missing reliable stacktrace support
Revert "livepatch: Remove reliable stacktrace check in klp_try_switch_task()"
stacktrace: Remove weak version of save_stack_trace_tsk_reliable()
livepatch: Use static buffer for debugging messages under rq lock
livepatch: Remove stale kobj_added entries from kernel-doc descriptions
WARN_ON_ONCE() could not be called safely under rq lock because
of console deadlock issues. Moreover WARN_ON_ONCE() is superfluous in
klp_check_stack(), because stack_trace_save_tsk_reliable() cannot return
-ENOSYS thanks to klp_have_reliable_stack() check in
klp_try_switch_task().
[ mbenes: changelog edited ]
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
This reverts commit 1d98a69e5c. Commit
31adf2308f ("livepatch: Convert error about unsupported reliable
stacktrace into a warning") weakened the enforcement for architectures
to have reliable stack traces support. The system only warns now about
it.
It only makes sense to reintroduce the compile time checking in
klp_try_switch_task() again and bail out early.
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
The err_buf array uses 128 bytes of stack space. Move it off the stack
by making it static. It's safe to use a shared buffer because
klp_try_switch_task() is called under klp_mutex.
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Based on 2 normalized pattern(s):
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details you
should have received a copy of the gnu general public license along
with this program if not see http www gnu org licenses
this program is free software you can redistribute it and or modify
it under the terms of the gnu general public license as published by
the free software foundation either version 2 of the license or at
your option any later version this program is distributed in the
hope that it will be useful but without any warranty without even
the implied warranty of merchantability or fitness for a particular
purpose see the gnu general public license for more details [based]
[from] [clk] [highbank] [c] you should have received a copy of the
gnu general public license along with this program if not see http
www gnu org licenses
extracted by the scancode license scanner the SPDX license identifier
GPL-2.0-or-later
has been chosen to replace the boilerplate/reference in 355 file(s).
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Jilayne Lovejoy <opensource@jilayne.com>
Reviewed-by: Steve Winslow <swinslow@gmail.com>
Reviewed-by: Allison Randal <allison@lohutok.net>
Cc: linux-spdx@vger.kernel.org
Link: https://lkml.kernel.org/r/20190519154041.837383322@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
The atomic replace allows to create cumulative patches. They are useful when
you maintain many livepatches and want to remove one that is lower on the
stack. In addition it is very useful when more patches touch the same function
and there are dependencies between them.
It's also a feature some of the distros are using already to distribute
their patches.
There are already macros to iterate over struct klp_func and klp_object.
Add also klp_for_each_patch(). But make it internal because also
klp_patches list is internal.
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
The fake signal is send automatically now. We can rely on it completely
and remove the sysfs attribute.
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
An administrator may send a fake signal to all remaining blocking tasks
of a running transition by writing to
/sys/kernel/livepatch/<patch>/signal attribute. Let's do it
automatically after 15 seconds. The timeout is chosen deliberately. It
gives the tasks enough time to transition themselves.
Theoretically, sending it once should be more than enough. However,
every task must get outside of a patched function to be successfully
transitioned. It could prove not to be simple and resending could be
helpful in that case.
A new workqueue job could be a cleaner solution to achieve it, but it
could also introduce deadlocks and cause more headaches with
synchronization and cancelling.
[jkosina@suse.cz: removed added newline]
Signed-off-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Replaced patches are removed from the stack when the transition is
finished. It means that Nop structures will never be needed again
and can be removed. Why should we care?
+ Nop structures give the impression that the function is patched
even though the ftrace handler has no effect.
+ Ftrace handlers do not come for free. They cause slowdown that might
be visible in some workloads. The ftrace-related slowdown might
actually be the reason why the function is no longer patched in
the new cumulative patch. One would expect that cumulative patch
would help solve these problems as well.
+ Cumulative patches are supposed to replace any earlier version of
the patch. The amount of NOPs depends on which version was replaced.
This multiplies the amount of scenarios that might happen.
One might say that NOPs are innocent. But there are even optimized
NOP instructions for different processors, for example, see
arch/x86/kernel/alternative.c. And klp_ftrace_handler() is much
more complicated.
+ It sounds natural to clean up a mess that is no longer needed.
It could only be worse if we do not do it.
This patch allows to unpatch and free the dynamic structures independently
when the transition finishes.
The free part is a bit tricky because kobject free callbacks are called
asynchronously. We could not wait for them easily. Fortunately, we do
not have to. Any further access can be avoided by removing them from
the dynamic lists.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Sometimes we would like to revert a particular fix. Currently, this
is not easy because we want to keep all other fixes active and we
could revert only the last applied patch.
One solution would be to apply new patch that implemented all
the reverted functions like in the original code. It would work
as expected but there will be unnecessary redirections. In addition,
it would also require knowing which functions need to be reverted at
build time.
Another problem is when there are many patches that touch the same
functions. There might be dependencies between patches that are
not enforced on the kernel side. Also it might be pretty hard to
actually prepare the patch and ensure compatibility with the other
patches.
Atomic replace && cumulative patches:
A better solution would be to create cumulative patch and say that
it replaces all older ones.
This patch adds a new "replace" flag to struct klp_patch. When it is
enabled, a set of 'nop' klp_func will be dynamically created for all
functions that are already being patched but that will no longer be
modified by the new patch. They are used as a new target during
the patch transition.
The idea is to handle Nops' structures like the static ones. When
the dynamic structures are allocated, we initialize all values that
are normally statically defined.
The only exception is "new_func" in struct klp_func. It has to point
to the original function and the address is known only when the object
(module) is loaded. Note that we really need to set it. The address is
used, for example, in klp_check_stack_func().
Nevertheless we still need to distinguish the dynamically allocated
structures in some operations. For this, we add "nop" flag into
struct klp_func and "dynamic" flag into struct klp_object. They
need special handling in the following situations:
+ The structures are added into the lists of objects and functions
immediately. In fact, the lists were created for this purpose.
+ The address of the original function is known only when the patched
object (module) is loaded. Therefore it is copied later in
klp_init_object_loaded().
+ The ftrace handler must not set PC to func->new_func. It would cause
infinite loop because the address points back to the beginning of
the original function.
+ The various free() functions must free the structure itself.
Note that other ways to detect the dynamic structures are not considered
safe. For example, even the statically defined struct klp_object might
include empty funcs array. It might be there just to run some callbacks.
Also note that the safe iterator must be used in the free() functions.
Otherwise already freed structures might get accessed.
Special callbacks handling:
The callbacks from the replaced patches are _not_ called by intention.
It would be pretty hard to define a reasonable semantic and implement it.
It might even be counter-productive. The new patch is cumulative. It is
supposed to include most of the changes from older patches. In most cases,
it will not want to call pre_unpatch() post_unpatch() callbacks from
the replaced patches. It would disable/break things for no good reasons.
Also it should be easier to handle various scenarios in a single script
in the new patch than think about interactions caused by running many
scripts from older patches. Not to say that the old scripts even would
not expect to be called in this situation.
Removing replaced patches:
One nice effect of the cumulative patches is that the code from the
older patches is no longer used. Therefore the replaced patches can
be removed. It has several advantages:
+ Nops' structs will no longer be necessary and might be removed.
This would save memory, restore performance (no ftrace handler),
allow clear view on what is really patched.
+ Disabling the patch will cause using the original code everywhere.
Therefore the livepatch callbacks could handle only one scenario.
Note that the complication is already complex enough when the patch
gets enabled. It is currently solved by calling callbacks only from
the new cumulative patch.
+ The state is clean in both the sysfs interface and lsmod. The modules
with the replaced livepatches might even get removed from the system.
Some people actually expected this behavior from the beginning. After all
a cumulative patch is supposed to "completely" replace an existing one.
It is like when a new version of an application replaces an older one.
This patch does the first step. It removes the replaced patches from
the list of patches. It is safe. The consistency model ensures that
they are no longer used. By other words, each process works only with
the structures from klp_transition_patch.
The removal is done by a special function. It combines actions done by
__disable_patch() and klp_complete_transition(). But it is a fast
track without all the transaction-related stuff.
Signed-off-by: Jason Baron <jbaron@akamai.com>
[pmladek@suse.com: Split, reuse existing code, simplified]
Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
The possibility to re-enable a registered patch was useful for immediate
patches where the livepatch module had to stay until the system reboot.
The improved consistency model allows to achieve the same result by
unloading and loading the livepatch module again.
Also we are going to add a feature called atomic replace. It will allow
to create a patch that would replace all already registered patches.
The aim is to handle dependent patches more securely. It will obsolete
the stack of patches that helped to handle the dependencies so far.
Then it might be unclear when a cumulative patch re-enabling is safe.
It would be complicated to support the many modes. Instead we could
actually make the API and code easier to understand.
Therefore, remove the two step public API. All the checks and init calls
are moved from klp_register_patch() to klp_enabled_patch(). Also the patch
is automatically freed, including the sysfs interface when the transition
to the disabled state is completed.
As a result, there is never a disabled patch on the top of the stack.
Therefore we do not need to check the stack in __klp_enable_patch().
And we could simplify the check in __klp_disable_patch().
Also the API and logic is much easier. It is enough to call
klp_enable_patch() in module_init() call. The patch can be disabled
by writing '0' into /sys/kernel/livepatch/<patch>/enabled. Then the module
can be removed once the transition finishes and sysfs interface is freed.
The only problem is how to free the structures and kobjects safely.
The operation is triggered from the sysfs interface. We could not put
the related kobject from there because it would cause lock inversion
between klp_mutex and kernfs locks, see kn->count lockdep map.
Therefore, offload the free task to a workqueue. It is perfectly fine:
+ The patch can no longer be used in the livepatch operations.
+ The module could not be removed until the free operation finishes
and module_put() is called.
+ The operation is asynchronous already when the first
klp_try_complete_transition() fails and another call
is queued with a delay.
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
module_put() is currently never called in klp_complete_transition() when
klp_force is set. As a result, we might keep the reference count even when
klp_enable_patch() fails and klp_cancel_transition() is called.
This might give the impression that a module might get blocked in some
strange init state. Fortunately, it is not the case. The reference count
is ignored when mod->init fails and erroneous modules are always removed.
Anyway, this might be confusing. Instead, this patch moves
the global klp_forced flag into struct klp_patch. As a result,
we block only modules that might still be in use after a forced
transition. Newly loaded livepatches might be eventually completely
removed later.
It is not a big deal. But the code is at least consistent with
the reality.
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
The address of the to be patched function and new function is stored
in struct klp_func as:
void *new_func;
unsigned long old_addr;
The different naming scheme and type are derived from the way
the addresses are set. @old_addr is assigned at runtime using
kallsyms-based search. @new_func is statically initialized,
for example:
static struct klp_func funcs[] = {
{
.old_name = "cmdline_proc_show",
.new_func = livepatch_cmdline_proc_show,
}, { }
};
This patch changes unsigned long old_addr -> void *old_func. It removes
some confusion when these address are later used in the code. It is
motivated by a followup patch that adds special NOP struct klp_func
where we want to assign func->new_func = func->old_addr respectively
func->new_func = func->old_func.
This patch does not modify the existing behavior.
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Alice Ferrazzi <alice.ferrazzi@gmail.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu(). This commit therefore makes this change,
even though it is but a comment.
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Support for immediate flag was removed by commit d0807da78e
("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 <kamalesh@linux.vnet.ibm.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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 <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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 <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
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 <mbenes@suse.cz>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: x86@kernel.org
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
