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

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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Merge branch 'master' into for-next

Sync with Linus' tree so that patches against newer codebase can be applied.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Merge tag 'v4.5' into next

Merge with Linux 4.5 to get PROPERTY_ENTRY_INTEGER() that is needed to
fix pxa/raumfeld rotary encoder properties.

Orangefs: merge to v4.5

Merge tag 'v4.5' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux into current

Linux 4.5

Merge branch 'topic/update-bits' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/regmap into asoc-rcar

Merge remote-tracking branch 'linusw-gpio/for-next' into devm_gpiochip

Base for demv_gpiochip_add_data() and devm_gpiochip_remove().

Merge tag 'v4.5-rc5' into asoc-mtk

Linux 4.5-rc5

Merge tag 'topic/drm-misc-2016-02-12' into drm-intel-next-queued

Backmerge to get at the new encoder_mask support in atomic helpers.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

Merge branch 'topic/acpi' of git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi into spi-pxa2xx

Merge branch 'x86/urgent' into x86/mm, to pick up dependent fix

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Merge branch 'linus' into efi/core, to refresh the branch and to pick up recent fixes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Merge tag 'v4.5-rc1' into x86/asm, to refresh the branch before merging new changes

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Merge branch 'enable-devices' into omap-for-v4.5/fixes

Merge tag 'v4.5-rc1' into patchwork

Linux 4.5-rc1

* tag 'v4.5-rc1': (11309 commits)
Linux 4.5-rc1
ideapad-laptop: Add Lenovo Yoga 700 to no_hw_rfkill dmi list
MAINTAINERS: Combine multiple te

Merge tag 'v4.5-rc1' into patchwork

Linux 4.5-rc1

* tag 'v4.5-rc1': (11309 commits)
Linux 4.5-rc1
ideapad-laptop: Add Lenovo Yoga 700 to no_hw_rfkill dmi list
MAINTAINERS: Combine multiple telemetry entries
intel_telemetry_debugfs: Fix unused warnings in telemetry debugfs
vmstat: Remove BUG_ON from vmstat_update
MIPS: zboot: Add support for serial debug using the PROM
MIPS: zboot: Avoid useless rebuilds
MIPS: BMIPS: Enable ARCH_WANT_OPTIONAL_GPIOLIB
MIPS: bcm63xx: nvram: Remove unused bcm63xx_nvram_get_psi_size() function
MIPS: bcm963xx: Update bcm_tag field image_sequence
MIPS: bcm963xx: Move extended flash address to bcm_tag header file
MIPS: bcm963xx: Move Broadcom BCM963xx image tag data structure
MIPS: bcm63xx: nvram: Use nvram structure definition from header file
MIPS: bcm963xx: Add Broadcom BCM963xx board nvram data structure
MAINTAINERS: Add KVM for MIPS entry
MIPS: KVM: Add missing newline to kvm_err()
MIPS: Move KVM specific opcodes into asm/inst.h
MIPS: KVM: Use cacheops.h definitions
MIPS: Break down cacheops.h definitions
MIPS: Use EXCCODE_ constants with set_except_vector()
...

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Merge tag 'kvm-s390-master-4.5-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

KVM: s390: Fixes for kvm/master (targeting 4.5)

1. Fallout of some bigger floating point/v

Merge tag 'kvm-s390-master-4.5-1' of git://git.kernel.org/pub/scm/linux/kernel/git/kvms390/linux into HEAD

KVM: s390: Fixes for kvm/master (targeting 4.5)

1. Fallout of some bigger floating point/vector rework in s390
- memory leak -> stable 4.3+
- memory overwrite -> stable 4.4+

2. enable KVM-VFIO for s390

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Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net

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

Pull livepatching updates from Jiri Kosina:

- RO/NX attribute fixes for patch module relocations from J

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

Pull livepatching updates from Jiri Kosina:

- RO/NX attribute fixes for patch module relocations from Josh
Poimboeuf. As part of this effort, module.c has been cleaned up as
well and livepatching is piggy-backing on this cleanup. Rusty is OK
with this whole lot going through livepatching tree.

- symbol disambiguation support from Chris J Arges. That series is
also

Reviewed-by: Miroslav Benes <mbenes@suse.cz>

but this came in only after I've alredy pushed out. Didn't want to
rebase because of that, hence I am mentioning it here.

- symbol lookup fix from Miroslav Benes

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching:
livepatch: Cleanup module page permission changes
module: keep percpu symbols in module's symtab
module: clean up RO/NX handling.
module: use a structure to encapsulate layout.
gcov: use within_module() helper.
module: Use the same logic for setting and unsetting RO/NX
livepatch: function,sympos scheme in livepatch sysfs directory
livepatch: add sympos as disambiguator field to klp_reloc
livepatch: add old_sympos as disambiguator field to klp_func

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livepatch: function,sympos scheme in livepatch sysfs directory

The following directory structure will allow for cases when the same
function name exists in a single object.
/sys/kernel/livepatch/<p

livepatch: function,sympos scheme in livepatch sysfs directory

The following directory structure will allow for cases when the same
function name exists in a single object.
/sys/kernel/livepatch/<patch>/<object>/<function,sympos>

The sympos number corresponds to the nth occurrence of the symbol name in
kallsyms for the patched object.

An example of patching multiple symbols can be found here:
https://github.com/dynup/kpatch/issues/493

Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

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Merge branch 'next' into for-linus

Prepare first round of input updates for 4.1 merge window.

Merge tag 'v4.0' into for_next

Linux 4.0

Merge branches 'for-4.0/upstream-fixes', 'for-4.1/genius', 'for-4.1/huion-uclogic-merge', 'for-4.1/i2c-hid', 'for-4.1/kconfig-drop-expert-dependency', 'for-4.1/logitech', 'for-4.1/multitouch', 'for-4

Merge branches 'for-4.0/upstream-fixes', 'for-4.1/genius', 'for-4.1/huion-uclogic-merge', 'for-4.1/i2c-hid', 'for-4.1/kconfig-drop-expert-dependency', 'for-4.1/logitech', 'for-4.1/multitouch', 'for-4.1/rmi', 'for-4.1/sony', 'for-4.1/upstream' and 'for-4.1/wacom' into for-linus

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Merge tag 'v4.0-rc5' into next

Merge with the latest upstream to synchronize Synaptics changes
and bring in new infrastructure pieces.

Conflicts:
drivers/input/mouse/synaptics.c

Merge branch 'sched/urgent' into sched/core, to pick up fixes before applying new patches

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Merge tag 'v4.0-rc5' into x86/fpu, to prevent conflicts

Signed-off-by: Ingo Molnar <mingo@kernel.org>

Merge tag 'v4.0-rc3' into x86/build, to refresh an older tree before applying new changes

Signed-off-by: Ingo Molnar <mingo@kernel.org>