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Author SHA1 Message Date
Miroslav Benes
c99a2be790 livepatch: force transition to finish 
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>
 2017-12-07 13:21:35 +01:00
Miroslav Benes
43347d56c8 livepatch: send a fake signal to all blocking tasks 
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>
 2017-12-04 22:34:57 +01:00
Greg Kroah-Hartman
b24413180f License cleanup: add SPDX GPL-2.0 license identifier to files with no license 
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 <5
   lines).

All documentation files were explicitly excluded.

The following heuristics were used to determine which SPDX license
identifiers to apply.

 - when both scanners couldn't find any license traces, file was
   considered to have no license information in it, and the top level
   COPYING file license applied.

   For non */uapi/* files that summary was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0                                              11139

   and resulted in the first patch in this series.

   If that file was a */uapi/* path one, it was "GPL-2.0 WITH
   Linux-syscall-note" otherwise it was "GPL-2.0".  Results of that was:

   SPDX license identifier                            # files
   ---------------------------------------------------|-------
   GPL-2.0 WITH Linux-syscall-note                        930

   and resulted in the second patch in this series.

 - if a file had some form of licensing information in it, and was one
   of the */uapi/* ones, it was denoted with the Linux-syscall-note if
   any GPL family license was found in the file or had no licensing in
   it (per prior point).  Results summary:

   SPDX license identifier                            # files
   ---------------------------------------------------|------
   GPL-2.0 WITH Linux-syscall-note                       270
   GPL-2.0+ WITH Linux-syscall-note                      169
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-2-Clause)    21
   ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)    17
   LGPL-2.1+ WITH Linux-syscall-note                      15
   GPL-1.0+ WITH Linux-syscall-note                       14
   ((GPL-2.0+ WITH Linux-syscall-note) OR BSD-3-Clause)    5
   LGPL-2.0+ WITH Linux-syscall-note                       4
   LGPL-2.1 WITH Linux-syscall-note                        3
   ((GPL-2.0 WITH Linux-syscall-note) OR MIT)              3
   ((GPL-2.0 WITH Linux-syscall-note) AND MIT)             1

   and that resulted in the third patch in this series.

 - when the two scanners agreed on the detected license(s), that became
   the concluded license(s).

 - when there was disagreement between the two scanners (one detected a
   license but the other didn't, or they both detected different
   licenses) a manual inspection of the file occurred.

 - In most cases a manual inspection of the information in the file
   resulted in a clear resolution of the license that should apply (and
   which scanner probably needed to revisit its heuristics).

 - When it was not immediately clear, the license identifier was
   confirmed with lawyers working with the Linux Foundation.

 - If there was any question as to the appropriate license identifier,
   the file was flagged for further research and to be revisited later
   in time.

In total, over 70 hours of logged manual review was done on the
spreadsheet to determine the SPDX license identifiers to apply to the
source files by Kate, Philippe, Thomas and, in some cases, confirmation
by lawyers working with the Linux Foundation.

Kate also obtained a third independent scan of the 4.13 code base from
FOSSology, and compared selected files where the other two scanners
disagreed against that SPDX file, to see if there was new insights.  The
Windriver scanner is based on an older version of FOSSology in part, so
they are related.

Thomas did random spot checks in about 500 files from the spreadsheets
for the uapi headers and agreed with SPDX license identifier in the
files he inspected. For the non-uapi files Thomas did random spot checks
in about 15000 files.

In initial set of patches against 4.14-rc6, 3 files were found to have
copy/paste license identifier errors, and have been fixed to reflect the
correct identifier.

Additionally Philippe spent 10 hours this week doing a detailed manual
inspection and review of the 12,461 patched files from the initial patch
version early this week with:
 - a full scancode scan run, collecting the matched texts, detected
   license ids and scores
 - reviewing anything where there was a license detected (about 500+
   files) to ensure that the applied SPDX license was correct
 - reviewing anything where there was no detection but the patch license
   was not GPL-2.0 WITH Linux-syscall-note to ensure that the applied
   SPDX license was correct

This produced a worksheet with 20 files needing minor correction.  This
worksheet was then exported into 3 different .csv files for the
different types of files to be modified.

These .csv files were then reviewed by Greg.  Thomas wrote a script to
parse the csv files and add the proper SPDX tag to the file, in the
format that the file expected.  This script was further refined by Greg
based on the output to detect more types of files automatically and to
distinguish between header and source .c files (which need different
comment types.)  Finally Greg ran the script using the .csv files to
generate the patches.

Reviewed-by: Kate Stewart <kstewart@linuxfoundation.org>
Reviewed-by: Philippe Ombredanne <pombredanne@nexb.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
 2017-11-02 11:10:55 +01:00
Josh Poimboeuf
d83a7cb375 livepatch: change to a per-task consistency model 
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.cz

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Ingo Molnar <mingo@kernel.org>        # for the scheduler changes
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
 2017-03-08 09:36:21 +01:00