netdev - Re: Issue accessing task_struct from BPF due to 4.16 stack-protector changes

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Message-ID: <20180302222643.qykmiqfvdesyiysm@ast-mbp.dhcp.thefacebook.com>
Date:   Fri, 2 Mar 2018 14:26:45 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Gianluca Borello <g.borello@...il.com>
Cc:     Linux Networking Development Mailing List 
        <netdev@...r.kernel.org>, Daniel Borkmann <daniel@...earbox.net>,
        Kees Cook <keescook@...omium.org>
Subject: Re: Issue accessing task_struct from BPF due to 4.16 stack-protector
 changes

On Fri, Mar 02, 2018 at 02:04:17PM -0800, Gianluca Borello wrote:
> On Fri, Mar 2, 2018 at 12:42 PM, Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > good catch!
> > I wonder why sched.h is using this flag insead of relying on #defines from autoconf.h
> > It could have been using CONFIG_HAVE_CC_STACKPROTECTOR
> > instead of CONFIG_CC_STACKPROTECTOR, no ?
> >
> 
> Thanks for your reply Alexei. I think switching to
> HAVE_CC_STACKPROTECTOR could indeed solve this particular BPF issue in
> a cleaner way (I tested it), at the cost of having that struct member
> always present for the supported architectures even if the stack
> protector is actually disabled (e.g. CONFIG_CC_STACKPROTECTOR_NONE=y).

if defined(HAVE_CC_STACKPROTECTOR) && !defined(CONFIG_CC_STACKPROTECTOR_NONE)

or

def(have_cc) && (def(cc_stack_regular) || def(cc_stack_strong) || def(cc_stack_auto))

let's fix it properly instead of adding more hacks to Makefiles