linux-kernel - Re: [PATCH] s390/kaslr: Fix casts in get

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Date:   Sat, 08 Feb 2020 12:17:20 -0800
From:   Joe Perches <joe@...ches.com>
To:     Nathan Chancellor <natechancellor@...il.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        clang-built-linux@...glegroups.com
Subject: Re: [PATCH] s390/kaslr: Fix casts in get_random

On Sat, 2020-02-08 at 07:10 -0700, Nathan Chancellor wrote:
> Clang warns:
> 
> ../arch/s390/boot/kaslr.c:78:25: warning: passing 'char *' to parameter
> of type 'const u8 *' (aka 'const unsigned char *') converts between
> pointers to integer
> types with different sign [-Wpointer-sign]
>                                   (char *) entropy, (char *) entropy,
>                                                     ^~~~~~~~~~~~~~~~
> ../arch/s390/include/asm/cpacf.h:280:28: note: passing argument to
> parameter 'src' here
>                             u8 *dest, const u8 *src, long src_len)
>                                                 ^
> 2 warnings generated.
> 
> Fix the cast to match what else is done in this function.
> 
> Fixes: b2d24b97b2a9 ("s390/kernel: add support for kernel address space layout randomization (KASLR)")
> Link: https://github.com/ClangBuiltLinux/linux/issues/862
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  arch/s390/boot/kaslr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/s390/boot/kaslr.c b/arch/s390/boot/kaslr.c
> index 5d12352545c5..5591243d673e 100644
> --- a/arch/s390/boot/kaslr.c
> +++ b/arch/s390/boot/kaslr.c
> @@ -75,7 +75,7 @@ static unsigned long get_random(unsigned long limit)
>  		*(unsigned long *) prng.parm_block ^= seed;
>  		for (i = 0; i < 16; i++) {
>  			cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block,
> -				  (char *) entropy, (char *) entropy,
> +				  (u8 *) entropy, (u8 *) entropy,

Why not change the function to take void *?

static inline int cpacf_kmc(unsigned long func, void *param,
			    u8 *dest, const u8 *src, long src_len)

vs:

static inline int cpacf_kmc(unsigned long func, void *param,
			    void *dest, const void *src, long src_len)

and remove the casts?