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    Subject[tip:x86/pti] jump_label: Warn on failed jump_label patching attempt
    Commit-ID:  5400c00440061515c5bda299c19b6e86b81be798
    Gitweb: https://git.kernel.org/tip/5400c00440061515c5bda299c19b6e86b81be798
    Author: Josh Poimboeuf <jpoimboe@redhat.com>
    AuthorDate: Tue, 20 Feb 2018 11:37:52 -0600
    Committer: Ingo Molnar <mingo@kernel.org>
    CommitDate: Wed, 21 Feb 2018 10:11:39 +0100

    jump_label: Warn on failed jump_label patching attempt

    Currently when the jump label code encounters an address which isn't
    recognized by kernel_text_address(), it just silently fails.

    This can be dangerous because jump labels are used in a variety of
    places, and are generally expected to work. Convert the silent failure
    to a warning.

    This won't warn about attempted writes to tracepoints in __init code
    after initmem has been freed, as those are already guarded by the
    entry->code check.

    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Acked-by: Peter Zijlstra <peterz@infradead.org>
    Cc: Borislav Petkov <bp@suse.de>
    Cc: Jason Baron <jbaron@akamai.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Steven Rostedt <rostedt@goodmis.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/de3a271c93807adb7ed48f4e946b4f9156617680.1519051220.git.jpoimboe@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    ---
    kernel/jump_label.c | 13 ++++++++-----
    1 file changed, 8 insertions(+), 5 deletions(-)

    diff --git a/kernel/jump_label.c b/kernel/jump_label.c
    index b717765..b2f0b47 100644
    --- a/kernel/jump_label.c
    +++ b/kernel/jump_label.c
    @@ -367,12 +367,15 @@ static void __jump_label_update(struct static_key *key,
    {
    for (; (entry < stop) && (jump_entry_key(entry) == key); entry++) {
    /*
    - * entry->code set to 0 invalidates module init text sections
    - * kernel_text_address() verifies we are not in core kernel
    - * init code, see jump_label_invalidate_module_init().
    + * An entry->code of 0 indicates an entry which has been
    + * disabled because it was in an init text area.
    */
    - if (entry->code && kernel_text_address(entry->code))
    - arch_jump_label_transform(entry, jump_label_type(entry));
    + if (entry->code) {
    + if (kernel_text_address(entry->code))
    + arch_jump_label_transform(entry, jump_label_type(entry));
    + else
    + WARN_ONCE(1, "can't patch jump_label at %pS", (void *)entry->code);
    + }
    }
    }

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