Subject: Re: [RFC] powerpc/64/module: REL32 relocation range check

From: Michael Ellerman <[email-masked]>
Date: Mon, 22 Oct 2018 20:36:51 +1100 (AEDT)

On Wed, 2018-08-29 at 11:56:56 UTC, Nicholas Piggin wrote:
> The recent module relocation overflow crash demonstrated that we
> have no range checking on REL32 relative relocations. This patch
> implements a basic check, the same kernel that previously oopsed
> and rebooted now continues with some of these errors when loading
> the module:
> 
>     module_64: x_tables: REL32 527703503449812 out of range!
> 
> Question is whether other relocations (ADDR32, REL16, TOC16, etc.)
> should also have overflow checks.
> ---
>  arch/powerpc/kernel/module_64.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index a2636c250b7b..2a2fb656d23b 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -678,7 +678,14 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
>  
>  		case R_PPC64_REL32:
>  			/* 32 bits relative (used by relative exception tables) */
> -			*(u32 *)location = value - (unsigned long)location;
> +			/* Convert value to relative */
> +			value -= (unsigned long)location;
> +			if (value + 0x80000000 > 0xffffffff) {
> +				pr_err("%s: REL32 %li out of range!\n",
> +				       me->name, (long int)value);
> +				return -ENOEXEC;
> +			}
> +			*(u32 *)location = value;
>  			break;
>  
>  		case R_PPC64_TOCSAVE:

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/b851ba02a6f3075f0f99c60c4bc30a

cheers