Re: [Xen-devel] [PATCH v2 00/12] livepatch: new features and fixes

[Julien Grall <julien.grall@arm.com>]

Hi,

Thank you for the new version. However, I nearly missed the v2 as this 
is a sub-thread of v1. May I ask you to send a new version as a new 
thread instead?

Cheers,

On 8/27/19 9:46 AM, Pawel Wieczorkiewicz wrote:
> This series introduces new features to the livepatch functionality as
> briefly discussed during Xen Developer Summit 2019: [a] and [b].
> It also provides a few fixes and some small improvements.
> 
> Main changes in v2:
> - added new features to livepatch documentation
> - added livepatch tests
> - enabled Arm support for [5]
> - make .modinfo optional for [11]
> - fixed typos
> 
> FEATURES:
> 
> 1. independent modules (patches: [1], [2])
> 
>    * livepatch-build-tools repo dependency [A]
> 
>    Livepatch enforces the following buildid-based dependency chain
>    between hotpatch modules:
>      1) first module depends on given hypervisor buildid
>      2) every consecutive module depends on previous module's buildid
>    This way proper hotpatch stack order is maintained and enforced.
>    While it is important for production hotpatches it limits agility and
>    blocks usage of testing or debug hotpatches. These kinds of hotpatch
>    modules are typically expected to be loaded at any time irrespective
>    of current state of the modules stack.
> 
>    [A] livepatch-build: Embed hypervisor build id into every hotpatch
> 
> 2. pre- and post- apply|revert actions hooks (patches: [3], [4])
> 
>    * livepatch-build-tools repo dependency [B]
> 
>    This is an implementation of 4 new livepatch module vetoing hooks,
>    that can be optionally supplied along with modules.
>    Hooks that currently exists in the livepatch mechanism aren't agile
>    enough and have various limitations:
>    * run only from within a quiescing zone
>    * cannot conditionally prevent applying or reverting
>    * do not have access to the module context
>    To address these limitations the following has been implemented:
>    1) pre-apply hook
>    2) post-apply hook
>    3) pre-revert hook
>    4) post-revert hook
> 
>    [B] create-diff-object: Handle extra pre-|post- hooks
> 
> 3. apply|revert actions replacement hooks (patches: [5], [6], [7])
> 
>    * livepatch-build-tools repo dependency: [C], [D], [E]
> 
>    To increase hotpatching system's agility and provide more flexiable
>    long-term hotpatch solution, allow to overwrite the default apply
>    and revert action functions with hook-like supplied alternatives.
>    The alternative functions are optional and the default functions are
>    used by default.
> 
>    [C] create-diff-object: Do not create empty .livepatch.funcs section
>    [D] create-diff-object: Handle optional apply|revert hooks
>    [E] create-diff-object: Add support for applied/reverted marker
> 
> 4. inline asm hotpatching expectations (patches: [8])
> 
>    * livepatch-build-tools repo dependency: [F]
> 
>    Expectations are designed as optional feature, since the main use of
>    them is planned for inline asm hotpatching.
>    The payload structure is modified as each expectation structure is
>    part of the livepatch_func structure and hence extends the payload.
>    The payload version is bumped to 3 with this change to highlight the
>    ABI modification and enforce proper support.
>    The expectation is manually enabled during inline asm module
>    construction. If enabled, expectation ensures that the expected
>    content of memory is to be found at a given patching (old_addr)
>    location.
> 
>    [F] create-diff-object: Add support for expectations
> 
> 5. runtime hotpatch metadata support (patches: [9], [10], [11])
> 
>    Having detailed hotpatch metadata helps to properly identify module's
>    origin and version. It also allows to keep track of the history of
>    hotpatch loads in the system (at least within dmesg buffer size
>    limits).
>    Extend the livepatch list operation to fetch also payloads' metadata.
>    This is achieved by extending the sysctl list interface with 2 extra
>    guest handles:
>    * metadata     - an array of arbitrary size strings
>    * metadata_len - an array of metadata strings' lengths (uin32_t each)
>    To unify and simplify the interface, handle the modules' name strings
>    of arbitrary size by copying them in adhering chunks to the userland.
> 
> 6. python bindings for livepatch operations (patches: [12])
> 
>    Extend the XC python bindings library to support all common livepatch
>    operations and actions:
>    - status (pyxc_livepatch_status):
>    - action (pyxc_livepatch_action):
>    - upload (pyxc_livepatch_upload):
>    - list (pyxc_livepatch_list):
> 
> [a] https://wiki.xenproject.org/wiki/Design_Sessions_2019#LivePatch_improvements_and_features
> [b] https://lists.xenproject.org/archives/html/xen-devel/2019-07/msg00846.html
> 
> Merged in v1:
>    python: Add XC binding for Xen build ID
>    livepatch: always print XENLOG_ERR information
> 
> Pawel Wieczorkiewicz (12):
>    [1] livepatch: Always check hypervisor build ID upon hotpatch upload
>    [2] livepatch: Allow to override inter-modules buildid dependency
>    [3] livepatch: Export payload structure via livepatch_payload.h
>    [4] livepatch: Implement pre-|post- apply|revert hooks
>    [5] livepatch: Add support for apply|revert action replacement hooks
>    [6] livepatch: Do not enforce ELF_LIVEPATCH_FUNC section presence
>    [7] livepatch: Add per-function applied/reverted state tracking marker
>    [8] livepatch: Add support for inline asm hotpatching expectations
>    [9] livepatch: Add support for modules .modinfo section metadata
>    [10] livepatch: Handle arbitrary size names with the list operation
>    [11] livepatch: Add metadata runtime retrieval mechanism
>    [12] livepatch: Add python bindings for livepatch operations
> 
>   .gitignore                                     |   6 +-
>   docs/misc/livepatch.pandoc                     | 231 ++++++++-
>   tools/libxc/include/xenctrl.h                  |  68 ++-
>   tools/libxc/xc_misc.c                          | 162 +++++--
>   tools/misc/xen-livepatch.c                     | 258 +++++++---
>   tools/python/xen/lowlevel/xc/xc.c              | 273 +++++++++++
>   xen/arch/arm/arm32/livepatch.c                 |  12 +-
>   xen/arch/arm/arm64/livepatch.c                 |  12 +-
>   xen/arch/arm/livepatch.c                       |  10 +-
>   xen/arch/x86/livepatch.c                       |  22 +-
>   xen/common/livepatch.c                         | 647 +++++++++++++++++++++----
>   xen/include/public/sysctl.h                    |  61 ++-
>   xen/include/xen/livepatch.h                    |  42 +-
>   xen/include/xen/livepatch_payload.h            |  83 ++++
>   xen/test/livepatch/Makefile                    | 113 ++++-
>   xen/test/livepatch/xen_action_hooks.c          | 102 ++++
>   xen/test/livepatch/xen_action_hooks_marker.c   | 112 +++++
>   xen/test/livepatch/xen_action_hooks_noapply.c  | 136 ++++++
>   xen/test/livepatch/xen_action_hooks_nofunc.c   |  86 ++++
>   xen/test/livepatch/xen_action_hooks_norevert.c | 143 ++++++
>   xen/test/livepatch/xen_expectations.c          |  41 ++
>   xen/test/livepatch/xen_expectations_fail.c     |  42 ++
>   xen/test/livepatch/xen_prepost_hooks.c         | 122 +++++
>   xen/test/livepatch/xen_prepost_hooks_fail.c    |  75 +++
>   24 files changed, 2579 insertions(+), 280 deletions(-)
>   create mode 100644 xen/test/livepatch/xen_action_hooks.c
>   create mode 100644 xen/test/livepatch/xen_action_hooks_marker.c
>   create mode 100644 xen/test/livepatch/xen_action_hooks_noapply.c
>   create mode 100644 xen/test/livepatch/xen_action_hooks_nofunc.c
>   create mode 100644 xen/test/livepatch/xen_action_hooks_norevert.c
>   create mode 100644 xen/test/livepatch/xen_expectations.c
>   create mode 100644 xen/test/livepatch/xen_expectations_fail.c
>   create mode 100644 xen/test/livepatch/xen_prepost_hooks.c
>   create mode 100644 xen/test/livepatch/xen_prepost_hooks_fail.c
> 

-- 
Julien Grall

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