Re: [PATCH 4/5] lkdtm: add usercopy tests

From: kbuild test robot <lkp@intel.com>
To: Kees Cook <keescook@chromium.org>
Cc: kbuild-all@01.org, kernel-hardening@lists.openwall.com,
	Kees Cook <keescook@chromium.org>, Arnd Bergmann <arnd@arndb.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"David S. Miller" <davem@davemloft.net>,
	Mauro Carvalho Chehab <mchehab@osg.samsung.com>,
	Jiri Slaby <jslaby@suse.cz>, Guenter Roeck <linux@roeck-us.net>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/5] lkdtm: add usercopy tests
Date: Wed, 8 Jun 2016 08:07:21 +0800	[thread overview]
Message-ID: <201606080821.2ILzOcsM%fengguang.wu@intel.com> (raw)
In-Reply-To: <1465336628-18219-5-git-send-email-keescook@chromium.org>

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Hi,

[auto build test WARNING on char-misc/char-misc-testing]
[also build test WARNING on v4.7-rc2 next-20160607]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Kees-Cook/lkdtm-add-usercopy-and-rodata-fix-atomic/20160608-060444
config: x86_64-randconfig-s2-06080621 (attached as .config)
compiler: gcc-6 (Debian 6.1.1-1) 6.1.1 20160430
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   drivers/misc/lkdtm_core.c: In function 'do_usercopy_stack_callee':
>> drivers/misc/lkdtm_core.c:420:9: warning: function may return address of local variable [-Wreturn-local-addr]
     return ptr;
            ^~~
   drivers/misc/lkdtm_core.c:405:16: note: declared here
     unsigned char buf[32];
                   ^~~

vim +420 drivers/misc/lkdtm_core.c

   404	{
   405		unsigned char buf[32];
   406		unsigned char *ptr = NULL;
   407		int i;
   408	
   409		/* Exercise stack to avoid everything living in registers. */
   410		for (i = 0; i < sizeof(buf); i++) {
   411			/*
   412			 * Hack to trick gcc into letting us return a reference
   413			 * to a local stack frame.
   414			 */
   415			if (i == 0)
   416				ptr = buf;
   417			buf[i] = value & 0xff;
   418		}
   419	
 > 420		return ptr;
   421	}
   422	
   423	static noinline void do_usercopy_stack(bool to_user)
   424	{
   425		unsigned long user_addr;
   426		unsigned char good_stack[32];
   427		unsigned char *bad_stack;
   428		int i;

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

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