Re: [PATCH REPOST] fs: Preventing READ_IMPLIES_EXEC Propagation

[Catalin Marinas <catalin.marinas@arm.com>]

On Tue, Apr 25, 2017 at 02:58:01PM +0800, dongbo (E) wrote:
> From: Dong Bo <dongbo4@huawei.com>
> 
> In load_elf_binary(), once the READ_IMPLIES_EXEC flag is set,
> the flag is propagated to its child processes, even the elf
> files are marked as not requiring executable stack. It may
> cause superfluous operations on some arch, e.g.
> __sync_icache_dcache on aarch64 due to a PROT_READ mmap is
> also marked as PROT_EXEC.
> 
> This patch was originally posted and discussed here:
> https://patchwork.kernel.org/patch/9685891/
> 
> Signed-off-by: Dong Bo <dongbo4@huawei.com>
> ---
>  fs/binfmt_elf.c       | 2 ++
>  fs/binfmt_elf_fdpic.c | 2 ++
>  2 files changed, 4 insertions(+)
> 
> diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
> index 5075fd5..c52e670 100644
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -863,6 +863,8 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  	SET_PERSONALITY2(loc->elf_ex, &arch_state);
>  	if (elf_read_implies_exec(loc->elf_ex, executable_stack))
>  		current->personality |= READ_IMPLIES_EXEC;
> +	else
> +		current->personality &= ~READ_IMPLIES_EXEC;
>   	if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space)
>  		current->flags |= PF_RANDOMIZE;
> diff --git a/fs/binfmt_elf_fdpic.c b/fs/binfmt_elf_fdpic.c
> index cf93a4f..c4bc4d0 100644
> --- a/fs/binfmt_elf_fdpic.c
> +++ b/fs/binfmt_elf_fdpic.c
> @@ -354,6 +354,8 @@ static int load_elf_fdpic_binary(struct linux_binprm *bprm)
>  		set_personality(PER_LINUX);
>  	if (elf_read_implies_exec(&exec_params.hdr, executable_stack))
>  		current->personality |= READ_IMPLIES_EXEC;
> +	else
> +		current->personality &= ~READ_IMPLIES_EXEC;
>   	setup_new_exec(bprm);
>  -- 1.9.1

FWIW, we queued the arm64-equivalent patch (commit 48f99c8ec0b25 in
linux-next). It doesn't change the behaviour for compat tasks since
we want to keep the same behaviour with arch/arm. If the above generic
patch gets merged, we'll drop the arm64-specific one.

-- 
Catalin