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    Subject[PATCH 0/2] Fix issue with alternatives/paravirt patches
    Date
    Hi,

    A few months ago, Chris Arges reported a bug involving alternatives/paravirt
    patching that was discussed here [1] and here [2]. To briefly summarize the
    bug, patch modules that contained .altinstructions or .parainstructions
    sections would break because these alternative/paravirt patches would be
    applied first by the module loader (see x86 module_finalize()), then
    livepatch would later clobber these patches when applying per-object
    relocations. This lead to crashes and unpredictable behavior.

    One conclusion we reached from our last discussion was that we will
    need to introduce some arch-specific code to address this problem.
    This patchset presents a possible fix for the bug by adding a new
    arch-specific arch_klp_init_object_loaded() function that by default
    does nothing but can be overridden by different arches.

    To fix this issue for x86, since we can access a patch module's Elf
    sections through mod->klp_info, we can simply delay the calls to
    apply_paravirt() and apply_alternatives() to arch_klp_init_object_loaded(),
    which is called after relocations have been written for an object.
    In addition, for patch modules, .parainstructions and .altinstructions are
    prefixed by ".klp.arch.${objname}" so that the module loader ignores them
    and livepatch can apply them manually.

    Currently for kpatch, we don't support including jump table sections in
    the patch module, and supporting .smp_locks is currently broken, so we
    don't consider those sections (for now).

    I did some light testing with some patches to kvm and verified that the
    original issue reported in [2] was fixed.

    Based on linux-next.

    [1] http://thread.gmane.org/gmane.linux.kernel/2185604/
    [2] https://github.com/dynup/kpatch/issues/580

    Jessica Yu (2):
    livepatch: use arch_klp_init_object_loaded() to finish arch-specific tasks
    livepatch/x86: apply alternatives and paravirt patches after relocations

    arch/x86/kernel/Makefile | 1 +
    arch/x86/kernel/livepatch.c | 66 +++++++++++++++++++++++++++++++++++++++++++++
    include/linux/livepatch.h | 3 +++
    kernel/livepatch/core.c | 12 +++++++--
    4 files changed, 80 insertions(+), 2 deletions(-)
    create mode 100644 arch/x86/kernel/livepatch.c

    --
    2.4.3

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