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    Subject[PATCH 4.15 076/163] objtool: Fix segfault in ignore_unreachable_insn()
    Date
    4.15-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Josh Poimboeuf <jpoimboe@redhat.com>

    commit fe24e27128252c230a34a6c628da2bf1676781ea upstream.

    Peter Zijlstra's patch for converting WARN() to use UD2 triggered a
    bunch of false "unreachable instruction" warnings, which then triggered
    a seg fault in ignore_unreachable_insn().

    The seg fault happened when it tried to dereference a NULL 'insn->func'
    pointer. Thanks to static_cpu_has(), some functions can jump to a
    non-function area in the .altinstr_aux section. That breaks
    ignore_unreachable_insn()'s assumption that it's always inside the
    original function.

    Make sure ignore_unreachable_insn() only follows jumps within the
    current function.

    Reported-by: Borislav Petkov <bp@alien8.de>
    Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: kbuild test robot <fengguang.wu@intel.com>
    Link: http://lkml.kernel.org/r/bace77a60d5af9b45eddb8f8fb9c776c8de657ef.1518130694.git.jpoimboe@redhat.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    tools/objtool/check.c | 12 +++++++++---
    1 file changed, 9 insertions(+), 3 deletions(-)

    --- a/tools/objtool/check.c
    +++ b/tools/objtool/check.c
    @@ -1935,13 +1935,19 @@ static bool ignore_unreachable_insn(stru
    if (is_kasan_insn(insn) || is_ubsan_insn(insn))
    return true;

    - if (insn->type == INSN_JUMP_UNCONDITIONAL && insn->jump_dest) {
    - insn = insn->jump_dest;
    - continue;
    + if (insn->type == INSN_JUMP_UNCONDITIONAL) {
    + if (insn->jump_dest &&
    + insn->jump_dest->func == insn->func) {
    + insn = insn->jump_dest;
    + continue;
    + }
    +
    + break;
    }

    if (insn->offset + insn->len >= insn->func->offset + insn->func->len)
    break;
    +
    insn = list_next_entry(insn, list);
    }


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