linux-hardening - [PATCH] MIPS: BCM47XX: Cast memcmp() of function to (void *)

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Date:   Wed,  7 Sep 2022 16:05:56 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Hauke Mehrtens <hauke@...ke-m.de>
Cc:     Kees Cook <keescook@...omium.org>,
        Rafał Miłecki <zajec5@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        linux-mips@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        llvm@...ts.linux.dev, kernel test robot <lkp@...el.com>,
        Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
        linux-hardening@...r.kernel.org
Subject: [PATCH] MIPS: BCM47XX: Cast memcmp() of function to (void *)

Clang is especially sensitive about argument type matching when using
__overloaded functions (like memcmp(), etc). Help it see that function
pointers are just "void *". Avoids this error:

arch/mips/bcm47xx/prom.c:89:8: error: no matching function for call to 'memcmp'
                   if (!memcmp(prom_init, prom_init + mem, 32))
                        ^~~~~~
include/linux/string.h:156:12: note: candidate function not viable: no known conversion from 'void (void)' to 'const void *' for 1st argument extern int memcmp(const void *,const void *,__kernel_size_t);

Cc: Hauke Mehrtens <hauke@...ke-m.de>
Cc: "Rafał Miłecki" <zajec5@...il.com>
Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: linux-mips@...r.kernel.org
Cc: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: llvm@...ts.linux.dev
Reported-by: kernel test robot <lkp@...el.com>
Link: https://lore.kernel.org/lkml/202209080652.sz2d68e5-lkp@intel.com
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/mips/bcm47xx/prom.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/bcm47xx/prom.c b/arch/mips/bcm47xx/prom.c
index ab203e66ba0d..eb5c04a24531 100644
--- a/arch/mips/bcm47xx/prom.c
+++ b/arch/mips/bcm47xx/prom.c
@@ -86,7 +86,7 @@ static __init void prom_init_mem(void)
 			pr_debug("Assume 128MB RAM\n");
 			break;
 		}
-		if (!memcmp(prom_init, prom_init + mem, 32))
+		if (!memcmp((void *)prom_init, (void *)prom_init + mem, 32))
 			break;
 	}
 	lowmem = mem;
-- 
2.34.1