1. 25 Jan, 2016 1 commit
    • Ard Biesheuvel's avatar
      arm64: hide __efistub_ aliases from kallsyms · 75feee3d
      Ard Biesheuvel authored
      Commit e8f3010f ("arm64/efi: isolate EFI stub from the kernel
      proper") isolated the EFI stub code from the kernel proper by prefixing
      all of its symbols with __efistub_, and selectively allowing access to
      core kernel symbols from the stub by emitting __efistub_ aliases for
      functions and variables that the stub can access legally.
      
      As an unintended side effect, these aliases are emitted into the
      kallsyms symbol table, which means they may turn up in backtraces,
      e.g.,
      
        ...
        PC is at __efistub_memset+0x108/0x200
        LR is at fixup_init+0x3c/0x48
        ...
        [<ffffff8008328608>] __efistub_memset+0x108/0x200
        [<ffffff8008094dcc>] free_initmem+0x2c/0x40
        [<ffffff8008645198>] kernel_init+0x20/0xe0
        [<ffffff8008085cd0>] ret_from_fork+0x10/0x40
      
      The backtrace in question has nothing to do with the EFI stub, but
      simply returns one of the several aliases of memset() that have been
      recorded in the kallsyms table. This is undesirable, since it may
      suggest to people who are not aware of this that the issue they are
      seeing is somehow EFI related.
      
      So hide the __efistub_ aliases from kallsyms, by emitting them as
      absolute linker symbols explicitly. The distinction between those
      and section relative symbols is completely irrelevant to these
      definitions, and to the final link we are performing when these
      definitions are being taken into account (the distinction is only
      relevant to symbols defined inside a section definition when performing
      a partial link), and so the resulting values are identical to the
      original ones. Since absolute symbols are ignored by kallsyms, this
      will result in these values to be omitted from its symbol table.
      
      After this patch, the backtrace generated from the same address looks
      like this:
        ...
        PC is at __memset+0x108/0x200
        LR is at fixup_init+0x3c/0x48
        ...
        [<ffffff8008328608>] __memset+0x108/0x200
        [<ffffff8008094dcc>] free_initmem+0x2c/0x40
        [<ffffff8008645198>] kernel_init+0x20/0xe0
        [<ffffff8008085cd0>] ret_from_fork+0x10/0x40
      Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
      Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
      75feee3d
  2. 24 Jan, 2016 39 commits