[PATCH v4] powerpc: Do not make the entire heap executable

Oleg Nesterov oleg at redhat.com
Wed Aug 10 23:36:21 AEST 2016

On 08/10, Denys Vlasenko wrote:
> Currently, to support 32-bit binaries with PLT in BSS kernel maps *entire
> brk area* with executable rights for all binaries, even --secure-plt ones.
> Stop doing that.

Can't really review this patch, but at least the change in mm/mmap.c looks
technically correct to me... One nit below, feel free to ignore.

> @@ -2668,7 +2668,7 @@ static int do_brk(unsigned long addr, unsigned long request)
>  	if (!len)
>  		return 0;
> -	flags = VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;
> +	flags |= VM_DATA_DEFAULT_FLAGS | VM_ACCOUNT | mm->def_flags;

OK. But note that we have


a few lines below and after this change this _looks_ wrong because
VM_LOCKED can come from the new "flags" argument passed to do_brk().
Nobody does this right now, still this looks wrong/confusing.

I'd suggest to add another change

	-	mlock_future_check(mm->def_flags);
	+	mlock_future_check(flags);

or add a sanity check at the start to deny VM_LOCKED and perhaps
something else...

The same for vm_brk_flags() which after your change does

	populate = (mm->def_flags & VM_LOCKED);

again, this is just a nit, I do not think it will be ever called
with VM_LOCKED in "flags".


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