linux-kernel - Re: [PATCH] structleak: disable BYREF_ALL in combination with KASAN

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Message-ID: <201906221324.C08C1EF@keescook>
Date:   Sat, 22 Jun 2019 13:26:02 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Alexander Popov <alex.popov@...ux.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        LSM List <linux-security-module@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] structleak: disable BYREF_ALL in combination with
 KASAN_STACK

On Fri, Jun 21, 2019 at 03:50:02PM +0200, Ard Biesheuvel wrote:
> On Fri, 21 Jun 2019 at 15:44, Arnd Bergmann <arnd@...db.de> wrote:
> > One pattern I have seen here is temporary variables from macros or
> > inline functions whose lifetime now extends over the entire function
> > rather than just the basic block in which they are defined, see e.g.
> > lpfc_debug_dump_qe() being inlined multiple times into
> > lpfc_debug_dump_all_queues(). Each instance of the local
> > "char line_buf[LPFC_LBUF_SZ];" seems to add on to the previous
> > one now, where the behavior without the structleak plugin is that
> > they don't.

Ewww.

> Right, that seems to be due to the fact that this code
> 
> /* split the first bb where we can put the forced initializers */
> gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
> bb = single_succ(ENTRY_BLOCK_PTR_FOR_FN(cfun));
> if (!single_pred_p(bb)) {
>     split_edge(single_succ_edge(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
>     gcc_assert(single_succ_p(ENTRY_BLOCK_PTR_FOR_FN(cfun)));
> }
> 
> puts all the initializers at the beginning of the function rather than
> inside the scope of the definition.

Do you see a sane way to improve this? I hadn't noticed that this
actually moved it up to the start of the function. :(

-- 
Kees Cook