Re: [PATCH 1/2] LoongArch: Avoid heap-buffer-overflow in loongarch_elf_relocate_section

[liuzhensong <liuzhensong@loongson.cn>]

[-- Attachment #1: Type: text/plain, Size: 4336 bytes --]


在 2022/9/15 上午10:56, Xi Ruoyao 写道:
> On Thu, 2022-09-15 at 09:47 +0800, liuzhensong wrote:
>>> How about this?  We don't need to write into the GOT if
>>> R_LARCH_RELATIVE
>>> or R_LARCH_IRELATIVE will be used:
>>   > "We don't need to write into the GOT if R_LARCH_RELATIVE or
>> R_LARCH_IRELATIVE will be used:"
>>
>> Not only this, you can refer to the implementation of the function
>> _bfd_elf_allocate_ifunc_dyn_relocs for details.
> I don't think _bfd_elf_allocate_ifunc_dyn_relocs (or
> local_allocate_ifunc_dyn_relocs for us) and
> loongarch_elf_relocate_section are strictly aligned.  We need to
> allocate the space for GOT entry, but no need to fill in the content if
> the entry will be resolved by R_LARCH_RELATIVE or R_LARCH_IRELATIVE
> because they are RELA and the "origin" value of the entry is not used
> during the resolution.

Some reasons of overflow.

>
> By the way, the code paths for REL can be also removed from
> local_allocate_ifunc_dyn_relocs because LoongArch does not use REL at
> all.
>
> And the change passes ld testsuite, the resulted ld passes glibc
> testsuite.
>
>>> diff --git a/bfd/elfnn-loongarch.c b/bfd/elfnn-loongarch.c
>>> index a9bb66a1e04..1e8ecb2b8e2 100644
>>> --- a/bfd/elfnn-loongarch.c
>>> +++ b/bfd/elfnn-loongarch.c
>>> @@ -3129,6 +3129,7 @@ loongarch_elf_relocate_section (bfd
>>> *output_bfd, struct bfd_link_info *info,
>>>                BFD_ASSERT (rel->r_addend == 0);
>>>     
>>>                bfd_vma got_off = 0;
>>> +             bool fill_got_entry = true;
>>>                if (h != NULL)
>>>                  {
>>>                    /* GOT ref or ifunc.  */
>>> @@ -3141,6 +3142,10 @@ loongarch_elf_relocate_section (bfd
>>> *output_bfd, struct bfd_link_info *info,
>>>                    if (h->got.offset == MINUS_ONE && h->type ==
>>> STT_GNU_IFUNC)
>>>                      {
>>>                        bfd_vma idx;
>>> +
>>> +                     /* An IFUNC is always resolved at runtime.  */

Not correct, anything can be filled if h->got.offset != MINUS_ONE.

There is no space for ifunc to fill got.

>>> +                     fill_got_entry = false;
>>> +
>>>                        if (htab->elf.splt != NULL)
>>>                          {
>>>                            idx = (h->plt.offset - PLT_HEADER_SIZE)
>>> @@ -3177,6 +3182,7 @@ loongarch_elf_relocate_section (bfd
>>> *output_bfd, struct bfd_link_info *info,
>>>                            rela.r_addend = relocation;
>>>                            loongarch_elf_append_rela (output_bfd,
>>>                                                       htab-
>>>> elf.srelgot, &rela);
>>> +                         fill_got_entry = false;
>>>                          }
>>>                        h->got.offset |= 1;
>>>                      }
>>> @@ -3197,12 +3203,14 @@ loongarch_elf_relocate_section (bfd
>>> *output_bfd, struct bfd_link_info *info,
>>>                            rela.r_addend = relocation;
>>>                            loongarch_elf_append_rela (output_bfd,
>>>                                                       htab-
>>>> elf.srelgot, &rela);
>>> +                         fill_got_entry = false;
>>>                          }
>>>                        local_got_offsets[r_symndx] |= 1;
>>>                      }
>>>                  }
>>>     
>>> -             bfd_put_NN (output_bfd, relocation, got->contents +
>>> got_off);
>>> +             if (fill_got_entry)
>>> +               bfd_put_NN (output_bfd, relocation, got->contents +
>>> got_off);
>>>     
>>>                relocation = got_off + sec_addr (got);
>>>              }
>>>