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

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Message-ID: <CAJWsiumzYg7+D1Tjp3vpWGQD2rutezY1HqZCuxLCT2Qih=g7Gg@mail.gmail.com>
Date:   Fri, 2 Mar 2018 14:04:17 -0800
From:   Gianluca Borello <g.borello@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...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 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).

Not sure if this could be frowned upon by someone considering how
critical task_struct is, but on the other hand is really just 8 bytes.

Thanks