[PATCH v2 1/2] ARM: handle interworking and out-of-range relocations separately

[Nicolas Pitre]

On Mon, 24 Nov 2014, Ard Biesheuvel wrote:

> Currently, interworking calls on module boundaries are not supported,
> and are handled by the same error handling code path as non-interworking
> calls whose targets are simply out of range.
> 
> Before modifying the handling of those out-of-range jump and call
> relocations in a subsequent patch, move the handling of interworking
> restrictions out of it.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>

Acked-by: Nicolas Pitre <nico at linaro.org>

> ---
>  arch/arm/kernel/module.c | 38 ++++++++++++++++++++++++--------------
>  1 file changed, 24 insertions(+), 14 deletions(-)
> 
> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> index 6a4dffefd357..16804df4857c 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -98,14 +98,19 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex,
>  		case R_ARM_PC24:
>  		case R_ARM_CALL:
>  		case R_ARM_JUMP24:
> +			if (sym->st_value & 3) {
> +				pr_err("%s: section %u reloc %u sym '%s': unsupported interworking call (ARM -> Thumb)\n",
> +				       module->name, relindex, i, symname);
> +				return -ENOEXEC;
> +			}
> +
>  			offset = __mem_to_opcode_arm(*(u32 *)loc);
>  			offset = (offset & 0x00ffffff) << 2;
>  			if (offset & 0x02000000)
>  				offset -= 0x04000000;
>  
>  			offset += sym->st_value - loc;
> -			if (offset & 3 ||
> -			    offset <= (s32)0xfe000000 ||
> +			if (offset <= (s32)0xfe000000 ||
>  			    offset >= (s32)0x02000000) {
>  				pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
>  				       module->name, relindex, i, symname,
> @@ -155,6 +160,22 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex,
>  #ifdef CONFIG_THUMB2_KERNEL
>  		case R_ARM_THM_CALL:
>  		case R_ARM_THM_JUMP24:
> +			/*
> +			 * For function symbols, only Thumb addresses are
> +			 * allowed (no interworking).
> +			 *
> +			 * For non-function symbols, the destination
> +			 * has no specific ARM/Thumb disposition, so
> +			 * the branch is resolved under the assumption
> +			 * that interworking is not required.
> +			 */
> +			if (ELF32_ST_TYPE(sym->st_info) == STT_FUNC &&
> +			    !(sym->st_value & 1)) {
> +				pr_err("%s: section %u reloc %u sym '%s': unsupported interworking call (Thumb -> ARM)\n",
> +				       module->name, relindex, i, symname);
> +				return -ENOEXEC;
> +			}
> +
>  			upper = __mem_to_opcode_thumb16(*(u16 *)loc);
>  			lower = __mem_to_opcode_thumb16(*(u16 *)(loc + 2));
>  
> @@ -182,18 +203,7 @@ apply_relocate(Elf32_Shdr *sechdrs, const char *strtab, unsigned int symindex,
>  				offset -= 0x02000000;
>  			offset += sym->st_value - loc;
>  
> -			/*
> -			 * For function symbols, only Thumb addresses are
> -			 * allowed (no interworking).
> -			 *
> -			 * For non-function symbols, the destination
> -			 * has no specific ARM/Thumb disposition, so
> -			 * the branch is resolved under the assumption
> -			 * that interworking is not required.
> -			 */
> -			if ((ELF32_ST_TYPE(sym->st_info) == STT_FUNC &&
> -				!(offset & 1)) ||
> -			    offset <= (s32)0xff000000 ||
> +			if (offset <= (s32)0xff000000 ||
>  			    offset >= (s32)0x01000000) {
>  				pr_err("%s: section %u reloc %u sym '%s': relocation %u out of range (%#lx -> %#x)\n",
>  				       module->name, relindex, i, symname,
> -- 
> 1.8.3.2
> 
>