[kernel-hardening] Re: [PATCH v2 00/29] implement KASLR for ARM

[Tony Lindgren <tony@atomide.com>]

* Ard Biesheuvel <ard.biesheuvel@linaro.org> [170905 12:43]:
> Right. Well, I will try to reproduce with the BB white I have.

Yeah that should be reproducable, I got it to happen on BBB here
after about 5 boots.

> Are you booting with an initrd?

Not on this one, on beagleboard xm I do.

> >> > Then loading modules with CONFIG_RANDOMIZE_BASE=y seems to fail with:
> >> >
> >> > $ sudo modprobe rtc-twl
> >> > rtc_twl: disagrees about version of symbol module_layout
> >> > modprobe: ERROR: could not insert 'rtc_twl': Exec format error
> >> >
> >>
> >> Is this with CONFIG_MODVERSIONS enabled?
> >
> > Yes, but disabling that did not seem to make any difference
> > based on just one test.
> >
> 
> Yeah, well, it appears I missed a couple of details :-)
> 
> This should fix the module loading issues:

Yeah now modprobe works :) That's after manually applying
it as the tabs got munched in your patch somewhere, see below.

Regards,

Tony

> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
> index 1a0304dd388d..bbefd5f32ec2 100644
> --- a/arch/arm/Kconfig
> +++ b/arch/arm/Kconfig
> @@ -1830,6 +1830,8 @@ config RANDOMIZE_BASE
>   depends on MMU && AUTO_ZRELADDR
>   depends on !XIP_KERNEL && !ZBOOT_ROM
>   select RELOCATABLE
> + select ARM_MODULE_PLTS if MODULES
> + select MODULE_REL_CRCS if MODVERSIONS
>   help
>    Randomizes the virtual and physical address at which the kernel
>    image is loaded, as a security feature that deters exploit attempts
> diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
> index f13ae153fb24..b56fc4dd27b6 100644
> --- a/arch/arm/include/asm/elf.h
> +++ b/arch/arm/include/asm/elf.h
> @@ -50,6 +50,7 @@ typedef struct user_fp elf_fpregset_t;
>  #define R_ARM_NONE 0
>  #define R_ARM_PC24 1
>  #define R_ARM_ABS32 2
> +#define R_ARM_REL32 3
>  #define R_ARM_CALL 28
>  #define R_ARM_JUMP24 29
>  #define R_ARM_TARGET1 38
> diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
> index 3ff571c2c71c..aa4d72837cd5 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -175,6 +175,10 @@
>   *(u32 *)loc |= offset & 0x7fffffff;
>   break;
> 
> + case R_ARM_REL32:
> + *(u32 *)loc += sym->st_value - loc;
> + break;
> +
>   case R_ARM_MOVW_ABS_NC:
>   case R_ARM_MOVT_ABS:
>   offset = tmp = __mem_to_opcode_arm(*(u32 *)loc);