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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Fri, 30 Jul 2021 10:08:03 -0700
Message-ID: <CAKwvOdmtKszUS0-OyGMHuhqjyXQC_283KOQOouWWtimYCvsAoA@mail.gmail.com>
Subject: Re: [PATCH 01/64] media: omap3isp: Extract struct group for memcpy() region
To:     Kees Cook <keescook@chromium.org>
Cc:     Dan Carpenter <dan.carpenter@oracle.com>, dsterba@suse.cz,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Bart Van Assche <bvanassche@acm.org>,
        linux-hardening@vger.kernel.org,
        "Gustavo A. R. Silva" <gustavoars@kernel.org>,
        Keith Packard <keithpac@amazon.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, linux-wireless@vger.kernel.org,
        netdev@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linux-staging@lists.linux.dev, linux-block@vger.kernel.org,
        linux-kbuild@vger.kernel.org, clang-built-linux@googlegroups.com,
        nborisov@suse.com
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On Fri, Jul 30, 2021 at 9:44 AM Kees Cook <keescook@chromium.org> wrote:
>
> On Fri, Jul 30, 2021 at 12:00:54PM +0300, Dan Carpenter wrote:
> > On Fri, Jul 30, 2021 at 10:38:45AM +0200, David Sterba wrote:
> > > Then is explicit memset the only reliable way accross all compiler
> > > flavors and supported versions?
> > >
> >
> > The = { } initializer works.  It's only when you start partially
> > initializing the struct that it doesn't initialize holes.
>
> No, partial works. It's when you _fully_ initialize the struct where the
> padding doesn't get initialized. *sob*

I'm pretty sure that this has more to do with whether or not the
compiler applies SROA then observes uses of the individual members or
not.

>
> struct foo {
>         u8 flag;
>         /* padding */
>         void *ptr;
> };
>
> These are fine:
>
> struct foo ok1 = { };
> struct foo ok2 = { .flag = 7 };
> struct foo ok3 = { .ptr = NULL };
>
> This is not:
>
> struct foo bad = { .flag = 7, .ptr = NULL };
>
> (But, of course, it depends on padding size, compiler version, and
> architecture. i.e. things remain unreliable.)
>
> --

-- 
Thanks,
~Nick Desaulniers