1. 12 Jul, 2023 1 commit
    • Yonghong Song's avatar
      kallsyms: strip LTO-only suffixes from promoted global functions · 8cc32a9b
      Yonghong Song authored
      Commit 6eb4bd92 ("kallsyms: strip LTO suffixes from static functions")
      stripped all function/variable suffixes started with '.' regardless
      of whether those suffixes are generated at LTO mode or not. In fact,
      as far as I know, in LTO mode, when a static function/variable is
      promoted to the global scope, '.llvm.<...>' suffix is added.
      
      The existing mechanism breaks live patch for a LTO kernel even if
      no <symbol>.llvm.<...> symbols are involved. For example, for the following
      kernel symbols:
        $ grep bpf_verifier_vlog /proc/kallsyms
        ffffffff81549f60 t bpf_verifier_vlog
        ffffffff8268b430 d bpf_verifier_vlog._entry
        ffffffff8282a958 d bpf_verifier_vlog._entry_ptr
        ffffffff82e12a1f d bpf_verifier_vlog.__already_done
      'bpf_verifier_vlog' is a static function. '_entry', '_entry_ptr' and
      '__already_done' are static variables used inside 'bpf_verifier_vlog',
      so llvm promotes them to file-level static with prefix 'bpf_verifier_vlog.'.
      Note that the func-level to file-level static function promotion also
      happens without LTO.
      
      Given a symbol name 'bpf_verifier_vlog', with LTO kernel, current mechanism will
      return 4 symbols to live patch subsystem which current live patching
      subsystem cannot handle it. With non-LTO kernel, only one symbol
      is returned.
      
      In [1], we have a lengthy discussion, the suggestion is to separate two
      cases:
        (1). new symbols with suffix which are generated regardless of whether
             LTO is enabled or not, and
        (2). new symbols with suffix generated only when LTO is enabled.
      
      The cleanup_symbol_name() should only remove suffixes for case (2).
      Case (1) should not be changed so it can work uniformly with or without LTO.
      
      This patch removed LTO-only suffix '.llvm.<...>' so live patching and
      tracing should work the same way for non-LTO kernel.
      The cleanup_symbol_name() in scripts/kallsyms.c is also changed to have the same
      filtering pattern so both kernel and kallsyms tool have the same
      expectation on the order of symbols.
      
       [1] https://lore.kernel.org/live-patching/20230615170048.2382735-1-song@kernel.org/T/#u
      
      Fixes: 6eb4bd92 ("kallsyms: strip LTO suffixes from static functions")
      Reported-by: default avatarSong Liu <song@kernel.org>
      Signed-off-by: default avatarYonghong Song <yhs@fb.com>
      Reviewed-by: default avatarZhen Lei <thunder.leizhen@huawei.com>
      Reviewed-by: default avatarNick Desaulniers <ndesaulniers@google.com>
      Acked-by: default avatarSong Liu <song@kernel.org>
      Link: https://lore.kernel.org/r/20230628181926.4102448-1-yhs@fb.comSigned-off-by: default avatarKees Cook <keescook@chromium.org>
      8cc32a9b
  2. 11 Jul, 2023 1 commit
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  4. 08 Jul, 2023 28 commits