linux-kernel - Re: [PATCH v2] crypto/caam: Avoid GCC constprop bug warning

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Message-ID: <202212021049.16C438A@keescook>
Date:   Fri, 2 Dec 2022 10:54:05 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Herbert Xu <herbert@...dor.apana.org.au>
Cc:     Horia Geantă <horia.geanta@....com>,
        Pankaj Gupta <pankaj.gupta@....com>,
        Gaurav Jain <gaurav.jain@....com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, kernel test robot <lkp@...el.com>,
        Anders Roxell <anders.roxell@...aro.org>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] crypto/caam: Avoid GCC constprop bug warning

On Fri, Dec 02, 2022 at 01:05:16PM +0800, Herbert Xu wrote:
> On Thu, Dec 01, 2022 at 07:30:22PM -0800, Kees Cook wrote:
> >
> > Getting rid of the if doesn't solve the warning. I can switch it to just
> > "if (data)", though. That keeps GCC happy.
> 
> OK I misread the thread.
> 
> Anyhow, it appears that this warning only occurs due to a debug
> printk in caam.  So how about something like this?

What? I don't think that's true? I think
CONFIG_CRYPTO_DEV_FSL_CAAM_DEBUG only controls "PRINT_POS", which is
unrelated?

The call path is:

drivers/crypto/caam/key_gen.c: gen_split_key()
	append_fifo_load_as_imm(..., NULL, ...) <- literal NULL
		append_cmd_data(..., data, ...)
			memcpy(..., data, ...)

and doesn't seem affected at all by CONFIG_CRYPTO_DEV_FSL_CAAM_DEBUG.

-Kees

> 
> diff --git a/drivers/crypto/caam/desc_constr.h b/drivers/crypto/caam/desc_constr.h
> index 62ce6421bb3f..b49c995e1cc6 100644
> --- a/drivers/crypto/caam/desc_constr.h
> +++ b/drivers/crypto/caam/desc_constr.h
> @@ -163,7 +163,7 @@ static inline void append_data(u32 * const desc, const void *data, int len)
>  {
>  	u32 *offset = desc_end(desc);
>  
> -	if (len) /* avoid sparse warning: memcpy with byte count of 0 */
> +	if (!IS_ENABLED(CONFIG_CRYPTO_DEV_FSL_CAAM_DEBUG) || data)
>  		memcpy(offset, data, len);
>  
>  	(*desc) = cpu_to_caam32(caam32_to_cpu(*desc) +

-- 
Kees Cook