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

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Date:   Mon, 17 Feb 2020 18:13:44 +0100
From:   Vasily Gorbik <gor@...ux.ibm.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Joe Perches <joe@...ches.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        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 Thu, Feb 13, 2020 at 11:46:28PM -0700, Nathan Chancellor wrote:
> On Sat, Feb 08, 2020 at 12:17:20PM -0800, Joe Perches wrote:
> > 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?
> 
> I can certainly do that if the maintainers prefer it.
> 
> Cheers,
> Nathan
KBUILD_CFLAGS contains -Wno-pointer-sign but special arch/s390/boot code
has a separate set of build flags. Anyhow the change makes sense as it is.
Applied to fixes, thanks