• Marc Zyngier's avatar
    kallsyms: Don't let kallsyms_lookup_size_offset() fail on retrieving the first symbol · 2a1a3fa0
    Marc Zyngier authored
    An arm64 kernel configured with
      # CONFIG_KALLSYMS_ALL is not set
    reports the following kprobe failure:
      [    0.032677] kprobes: failed to populate blacklist: -22
      [    0.033376] Please take care of using kprobes.
    It appears that kprobe fails to retrieve the symbol at address
    0xffff000010081000, despite this symbol being in System.map:
      ffff000010081000 T __exception_text_start
    This symbol is part of the first group of aliases in the
    kallsyms_offsets array (symbol names generated using ugly hacks in
              .long   0x1000 // do_undefinstr
              .long   0x1000 // efi_header_end
              .long   0x1000 // _stext
              .long   0x1000 // __exception_text_start
              .long   0x12b0 // do_cp15instr
    Looking at the implementation of get_symbol_pos(), it returns the
    lowest index for aliasing symbols. In this case, it return 0.
    But kallsyms_lookup_size_offset() considers 0 as a failure, which
    is obviously wrong (there is definitely a valid symbol living there).
    In turn, the kprobe blacklisting stops abruptly, hence the original
    A CONFIG_KALLSYMS_ALL kernel wouldn't fail as there is always
    some random symbols at the beginning of this array, which are never
    looked up via kallsyms_lookup_size_offset.
    Fix it by considering that get_symbol_pos() is always successful
    (which is consistent with the other uses of this function).
    Fixes: ffc50891
     ("[PATCH] Create kallsyms_lookup_size_offset()")
    Reviewed-by: default avatarMasami Hiramatsu <mhiramat@kernel.org>
    Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Will Deacon <will@kernel.org>
    Cc: Catalin Marinas <catalin.marinas@arm.com>
    Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
    Signed-off-by: default avatarWill Deacon <will@kernel.org>
kallsyms.c 17.6 KB