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    Subject[tip:core/core] jump_label: Implement generic support for relative references
    Commit-ID:  50ff18ab497aa22f6a59444625df7508c8918237
    Gitweb: https://git.kernel.org/tip/50ff18ab497aa22f6a59444625df7508c8918237
    Author: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    AuthorDate: Tue, 18 Sep 2018 23:51:37 -0700
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Thu, 27 Sep 2018 17:56:47 +0200

    jump_label: Implement generic support for relative references

    To reduce the size taken up by absolute references in jump label
    entries themselves and the associated relocation records in the
    .init segment, add support for emitting them as relative references
    instead.

    Note that this requires some extra care in the sorting routine, given
    that the offsets change when entries are moved around in the jump_entry
    table.

    Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: linux-arm-kernel@lists.infradead.org
    Cc: linux-s390@vger.kernel.org
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
    Cc: Kees Cook <keescook@chromium.org>
    Cc: Will Deacon <will.deacon@arm.com>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
    Cc: Jessica Yu <jeyu@kernel.org>
    Link: https://lkml.kernel.org/r/20180919065144.25010-3-ard.biesheuvel@linaro.org

    ---
    arch/Kconfig | 3 +++
    include/linux/jump_label.h | 28 ++++++++++++++++++++++++++++
    kernel/jump_label.c | 22 +++++++++++++++++++++-
    3 files changed, 52 insertions(+), 1 deletion(-)

    diff --git a/arch/Kconfig b/arch/Kconfig
    index 6801123932a5..9d329608913e 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -359,6 +359,9 @@ config HAVE_PERF_USER_STACK_DUMP
    config HAVE_ARCH_JUMP_LABEL
    bool

    +config HAVE_ARCH_JUMP_LABEL_RELATIVE
    + bool
    +
    config HAVE_RCU_TABLE_FREE
    bool

    diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
    index 2eadff9b3b90..2768a925bafa 100644
    --- a/include/linux/jump_label.h
    +++ b/include/linux/jump_label.h
    @@ -121,6 +121,32 @@ struct static_key {
    #include <asm/jump_label.h>

    #ifndef __ASSEMBLY__
    +#ifdef CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE
    +
    +struct jump_entry {
    + s32 code;
    + s32 target;
    + long key; // key may be far away from the core kernel under KASLR
    +};
    +
    +static inline unsigned long jump_entry_code(const struct jump_entry *entry)
    +{
    + return (unsigned long)&entry->code + entry->code;
    +}
    +
    +static inline unsigned long jump_entry_target(const struct jump_entry *entry)
    +{
    + return (unsigned long)&entry->target + entry->target;
    +}
    +
    +static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
    +{
    + long offset = entry->key & ~1L;
    +
    + return (struct static_key *)((unsigned long)&entry->key + offset);
    +}
    +
    +#else

    static inline unsigned long jump_entry_code(const struct jump_entry *entry)
    {
    @@ -137,6 +163,8 @@ static inline struct static_key *jump_entry_key(const struct jump_entry *entry)
    return (struct static_key *)((unsigned long)entry->key & ~1UL);
    }

    +#endif
    +
    static inline bool jump_entry_is_branch(const struct jump_entry *entry)
    {
    return (unsigned long)entry->key & 1UL;
    diff --git a/kernel/jump_label.c b/kernel/jump_label.c
    index 834e43de0daf..898a1d0c38dc 100644
    --- a/kernel/jump_label.c
    +++ b/kernel/jump_label.c
    @@ -47,14 +47,34 @@ static int jump_label_cmp(const void *a, const void *b)
    return 0;
    }

    +static void jump_label_swap(void *a, void *b, int size)
    +{
    + long delta = (unsigned long)a - (unsigned long)b;
    + struct jump_entry *jea = a;
    + struct jump_entry *jeb = b;
    + struct jump_entry tmp = *jea;
    +
    + jea->code = jeb->code - delta;
    + jea->target = jeb->target - delta;
    + jea->key = jeb->key - delta;
    +
    + jeb->code = tmp.code + delta;
    + jeb->target = tmp.target + delta;
    + jeb->key = tmp.key + delta;
    +}
    +
    static void
    jump_label_sort_entries(struct jump_entry *start, struct jump_entry *stop)
    {
    unsigned long size;
    + void *swapfn = NULL;
    +
    + if (IS_ENABLED(CONFIG_HAVE_ARCH_JUMP_LABEL_RELATIVE))
    + swapfn = jump_label_swap;

    size = (((unsigned long)stop - (unsigned long)start)
    / sizeof(struct jump_entry));
    - sort(start, size, sizeof(struct jump_entry), jump_label_cmp, NULL);
    + sort(start, size, sizeof(struct jump_entry), jump_label_cmp, swapfn);
    }

    static void jump_label_update(struct static_key *key);
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