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    SubjectRe: [PATCH 13/24] objtool: Implement base jump_assert support
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    On Tue, 2018-01-23 at 16:25 +0100, Peter Zijlstra wrote:
    > Implement a jump_label assertion that asserts that the code location
    > is indeed only reachable through a static_branch. Because if GCC is
    > absolutely retaded it could generate code like:
    >
    >         xor rax,rax
    >         NOP/JMP 1f
    >         mov $1, rax
    > 1:
    >         test rax,rax
    >         jz 2f
    >         
    > 2:
    >
    > instead of the sensible:
    >
    >         NOP/JMP 1f
    >         
    > 1:
    >
    > This implements objtool infrastructure for ensuring the code ends up
    > sane, since we'll rely on that for correctness and security.
    >
    > We tag the instructions after the static branch with static_jump_dest=true;
    > that is the instruction after the NOP and the instruction at the
    > JMP+disp site.
    >
    > Then, when we read the .discard.jump_assert section, we assert that
    > each entry points to an instruction that has static_jump_dest set.
    >
    > With this we can assert that the code emitted for the if statement
    > ends up at the static jump location and nothing untowards happened.
    >
    > Cc: Thomas Gleixner <tglx@linutronix.de>
    > Cc: Borislav Petkov <bp@alien8.de>
    > Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    >
    > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

    Thank you for pandering to my paranoia. I suspect that misspelling the
    word 'retarded' isn't going to be sufficient to stop people from
    objecting to the use of that word, but other than that,

    Reviewed-by: David Woodhouse <dwmw@amazon.co.uk>
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