From: Kees Cook <keescook@chromium.org>
To: Eric Biggers <ebiggers@kernel.org>
Cc: "Horia Geantă" <horia.geanta@nxp.com>,
"Herbert Xu" <herbert@gondor.apana.org.au>,
"Pankaj Gupta" <pankaj.gupta@nxp.com>,
"Gaurav Jain" <gaurav.jain@nxp.com>,
"David S. Miller" <davem@davemloft.net>,
linux-crypto@vger.kernel.org, "kernel test robot" <lkp@intel.com>,
"Anders Roxell" <anders.roxell@linaro.org>,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2] crypto/caam: Avoid GCC constprop bug warning
Date: Thu, 1 Dec 2022 19:23:49 -0800 [thread overview]
Message-ID: <202212011920.A6648E9B@keescook> (raw)
In-Reply-To: <Y4ludwin631WFhcG@sol.localdomain>
On Thu, Dec 01, 2022 at 07:18:15PM -0800, Eric Biggers wrote:
> On Thu, Dec 01, 2022 at 05:04:14PM -0800, Kees Cook wrote:
> > GCC 12 appears to perform constant propagation incompletely(?) and can
> > no longer notice that "len" is always 0 when "data" is NULL. Expand the
> > check to avoid warnings about memcpy() having a NULL argument:
>
> Is there a gcc option to turn off the "memcpy with NULL and len=0 is undefined
> behavior" thing? It's basically a bug in the C standard.
It's not undefined -- it's just pedantic. __builtin_memcpy is defined
internally to GCC with __attribute__((nonnull (1, 2))), and since it can
find a path from an always-NULL argument, it warns. I think it's a dumb
limitation, given that "zero size to/from NULL" is perfectly valid.
--
Kees Cook
next prev parent reply other threads:[~2022-12-02 3:23 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-02 1:04 [PATCH v2] crypto/caam: Avoid GCC constprop bug warning Kees Cook
2022-12-02 2:50 ` Herbert Xu
2022-12-02 3:30 ` Kees Cook
2022-12-02 5:05 ` Herbert Xu
2022-12-02 18:54 ` Kees Cook
2022-12-02 23:36 ` Herbert Xu
2022-12-02 3:18 ` Eric Biggers
2022-12-02 3:23 ` Kees Cook [this message]
2022-12-02 3:32 ` Eric Biggers
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