Re: [question] insert ko failed because count_plts return 0 when CONFIG_RANDOMIZE_BASE is not set

[Ard Biesheuvel <ardb@kernel.org>]

On Wed, 24 Mar 2021 at 08:27, chenjun (AM) <chenjun102@huawei.com> wrote:
>
> Hi
>
> I make a Image for arm64 (without CONFIG_RANDOMIZE_BASE). And a ko (13M)
> can not be inserted.
>

How many large modules have you loaded already? The module region is
only 128 MB, so if your modules are huge, you may run out of space.

Please check the kernel VA address and the load address of the module,
and check whether they are more than 128 MB apart.


> WARNING: CPU: 2 PID: 1998 at arch/arm64/kernel/module-plts.c:39
> module_emit_plt_entry+0x100/0x118
> ...
> Call trace:
> module_emit_plt_entry+0x100/0x118
> apply_relocate_add+0x34c/0x570
> ...
>
> I think the problem is that:
> in apply_relocate_add:
>                   case R_AARCH64_CALL26:
>                       ovf = reloc_insn_imm(RELOC_OP_PREL, loc, val, 2, 26,
>                                                AARCH64_INSN_IMM_26);
>
>                       if (IS_ENABLED(CONFIG_ARM64_MODULE_PLTS) &&
>                           ovf == -ERANGE) {
>                               val = module_emit_plt_entry(me, sechdrs,
> loc, &rel[i], sym); realoc_insn_imm return -ERANGE (because the ko is
> too big?)
>
> in module_emit_plt_entry:
> WARN_ON(pltsec->plt_num_entries > pltsec->plt_max_entries)
> pltsec->plt_max_entries is 0 if CONFIG_RANDOMIZE_BASE is not be set.
>
> a257e02 arm64/kernel: don't ban ADRP to work around Cortex-A53 erratum
> #843419
>    static unsigned int count_plts(Elf64_Sym *syms, Elf64_Rela *rela, int
> num,
> -                              Elf64_Word dstidx)
> +                              Elf64_Word dstidx, Elf_Shdr *dstsec)
>    {
> ...
>                   switch (ELF64_R_TYPE(rela[i].r_info)) {
>                   case R_AARCH64_JUMP26:
>                   case R_AARCH64_CALL26:
> +                       if (!IS_ENABLED(CONFIG_RANDOMIZE_BASE))
> +                               break;
> +
>
> Why we need break if !IS_ENABLED(CONFIG_RANDOMIZE_BASE)? or any
> restrictions on ko?
>
> I comment out this part of the code. the ko could be inserted, and seems
> to work well. So is it a accepted way? or any solution for my case?
>
> --
> Regards
> Chen Jun
>