mirror of https://gitee.com/openkylin/linux.git
7 Commits
| Author | SHA1 | Message | Date |
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Josh Poimboeuf
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3ec24776bf |
livepatch: allow removal of a disabled patch
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
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Josh Poimboeuf
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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>
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Linus Torvalds
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c1aac62f36 |
A slightly quieter cycle for documentation this time around.
Three more DocBook template files have been converted to RST; only 21 to go. There are various build improvements and the usual array of documentation improvements and fixes. -----BEGIN PGP SIGNATURE----- iQIcBAABAgAGBQJYriFXAAoJEI3ONVYwIuV6iTMP/iV7ownq9IK1f8askcXKM76i NoRdj4/JywAPQ73vLhOSDVELGdVJNRBjdyOdBRzxPgsqAhFmm79lVYV2eLIffQ2k 7LcVbEQR77I+4z9SwqIVbIWNCBry7Hu8aWh7moDL3I6yeuay408yr5YW2lIlsqHZ V/LZgkTWDe+iQPeXNA4Djzylx0lcRlAy4yMSLjN1+gb9/uBnXb9J0eGJzgfZfrL8 fiIhymg3bv8vB99l6LMR5vT343QLWXf1yS31A7rPQvwkDo6zFehUJA0XNfIsl2dw VQYsvl9vp9wy3e6Y0qKXPn1XhAhCrm64P3crBxK31MMvcKZVCfeRSZ78wrvpvewy MVLlXdqop1bHPHowtRfA5jwxr1NqcYp+Jg0+YGX3iXpPi1Jfk36DNUy9iWvtvIzr lWgQcIKsdCwwYUcvPR8Kt8T/3q/AHbYlI6mimWlkmbZwncQcgCrH5xSG+c2BIPfV fn3W6eLHBn8RyVsxlaXlA0Y9TNtI/Cm85b3Ri10pFvhl868ppWfJxXHi7UtcbU58 sQzahISCTXOH/NQwkkh7kFMtczbB43rAcChvF7EUYpazVBpJ4P4HxKFg3eIzIdc6 VlBSaMu1hxUGoYxNNYuKr/nYstuczLOKzK7q4j/JOExY3RgTWP+T3bF02wgubvoa D/9WfScewkgCJRoA7i17 =C5nd -----END PGP SIGNATURE----- Merge tag 'docs-4.11' of git://git.lwn.net/linux Pull documentation updates from Jonathan Corbet: "A slightly quieter cycle for documentation this time around. Three more DocBook template files have been converted to RST; only 21 to go. There are various build improvements and the usual array of documentation improvements and fixes" * tag 'docs-4.11' of git://git.lwn.net/linux: (44 commits) docs / driver-api: Fix structure references in device_link.rst PM / docs: Fix structure references in device.rst Add a target to check broken external links in the Documentation Documentation: Fix linux-api list typo Documentation: DocBook/Makefile comment typo Improve sparse documentation Documentation: make Makefile.sphinx no-ops quieter Documentation: DMA-ISA-LPC.txt Documentation: input: fix path to input code definitions docs: Remove the copyright year from conf.py docs: Fix a warning in the Korean HOWTO.rst translation PM / sleep / docs: Convert PM notifiers document to reST PM / core / docs: Convert sleep states API document to reST PM / core: Update kerneldoc comments in pm.h doc-rst: Fix recursive make invocation from macros doc-rst: Delete output of failed dot-SVG conversion doc-rst: Break shell command sequences on failure Documentation/sphinx: make targets independent of Sphinx work for HAVE_SPHINX=0 doc-rst: fixed cleandoc target when used with O=dir Documentation/sphinx: prevent generation of .pyc files in the source tree ... |
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Masanari Iida
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8da9704c8b |
Doc: Fix double words in Documentation
This patch fix some double words found in Documentation. Signed-off-by: Masanari Iida <standby24x7@gmail.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net> |
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Miroslav Benes
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372e2db721 |
livepatch: doc: remove the limitation for schedule() patching
The Limitations section of the documentation describes the impossibility
to livepatch anything that is inlined to __schedule() function. This had
been true till 4.9 kernel came. Thanks to commit
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Petr Mladek
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59024954a1 |
Documentation/livepatch: Fix stale link to gmame
gmame archive does not longer exist. Use the message id and generic redirector instead. Reported-by: John Donnelly <john.donnelly@canonical.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz> |
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Petr Mladek
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5e4e38446a |
livepatch: Add some basic livepatch documentation
livepatch framework deserves some documentation, definitely. This is an attempt to provide some basic info. I hope that it will be useful for both LivePatch producers and also potential developers of the framework itself. [jkosina@suse.cz: - incorporated feedback (grammar fixes) from Chris J Arges <chris.j.arges@canonical.com> - s/LivePatch/livepatch in changelog as pointed out by Josh Poimboeuf <jpoimboe@redhat.com> - incorporated part of feedback (grammar fixes / reformulations) from Balbir Singh <bsingharora@gmail.com> ] Acked-by: Jessica Yu <jeyu@redhat.com> Signed-off-by: Petr Mladek <pmladek@suse.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz> |