Re: [PATCH v2] binfmt_elf: Fix PIE execution with randomization disabled (was Re: [RFC PATCH] binfmt_elf: Fix PIE execution with randomization disabled)

[Nicolas Pitre <nicolas.pitre@linaro.org>]

On Mon, 3 Oct 2011, Jiri Kosina wrote:

> How about the patch below instead? It survives my testing, and I believe 
> it handles both cases properly.
> 
> Confirmation from the original bug reporter would obviously be a nice 
> bonus too :)
> 
> 
> 
> 
> From: Jiri Kosina <jkosina@suse.cz>
> Subject: [PATCH] binfmt_elf: fix PIE execution with randomization disabled
> 
> The case of address space randomization being disabled in runtime through
> randomize_va_space sysctl is not treated properly in load_elf_binary(),
> resulting in SIGKILL coming at exec() time for certain PIE-linked binaries
> in case the randomization has been disabled at runtime prior to calling
> exec().
> 
> Handle the randomize_va_space == 0 case the same way as if we were not
> supporting .text randomization at all.
> 
> Based on original patch by H.J. Lu <hongjiu.lu@intel.com> and
> Josh Boyer <jwboyer@redhat.com>
> 
> Cc: Ingo Molnar <mingo@elte.hu>
> Cc: Jiri Kosina <jkosina@suse.cz>
> Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
> Cc: Russell King <rmk@arm.linux.org.uk>
> Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>

However I'd suggest a change to deal with style issues:

> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index dd0fdfc..bb11fe4 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -795,7 +795,10 @@ static int load_elf_binary(struct linux_binprm *bprm, struct pt_regs *regs)
>  			 * might try to exec.  This is because the brk will
>  			 * follow the loader, and is not movable.  */
>  #if defined(CONFIG_X86) || defined(CONFIG_ARM)
> -			load_bias = 0;
> +			if (current->flags & PF_RANDOMIZE)
> +				load_bias = 0;
> +			else
> +				load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
>  #else
>  			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
>  #endif

What about this instead, saving 3 lines out of 8:

			load_bias = ELF_PAGESTART(ELF_ET_DYN_BASE - vaddr);
#if defined(CONFIG_X86) || defined(CONFIG_ARM)
			if (current->flags & PF_RANDOMIZE)
				load_bias = 0;
#endif


?


Nicolas