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Date:   Thu, 1 Dec 2022 19:18:15 -0800
From:   Eric Biggers <ebiggers@kernel.org>
To:     Kees Cook <keescook@chromium.org>
Cc:     Horia =?utf-8?Q?Geant=C4=83?= <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
Message-ID: <Y4ludwin631WFhcG@sol.localdomain>
References: <20221202010410.gonna.444-kees@kernel.org>
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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.

Note that the kernel already uses options that make other types of undefined
behavior defined: -fno-strict-overflow, -fno-strict-aliasing, and
-fno-delete-null-pointer-checks.

- Eric