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

[liuzhensong]

在 2022/9/14 下午7:15, Xi Ruoyao 写道:
> On Wed, 2022-09-14 at 18:15 +0800, Xi Ruoyao via Binutils wrote:
>
>>> Shouldn't write to got table when using hidden ifunc.
>> Perhaps it's true, using RELA to resolve a GOT entry should not depend
>> on any "initial" value of the entry...
>
> 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.

>
> 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.  */
> +		      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);
>   	    }
>