netdev - Re: [PATCH v4 4/9] em28xx: fix em28xx_dvb

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Date:   Mon, 2 Oct 2017 10:33:37 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Andrey Ryabinin <aryabinin@...tuozzo.com>
Cc:     David Laight <David.Laight@...lab.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Jiri Pirko <jiri@...nulli.us>,
        Arend van Spriel <arend.vanspriel@...adcom.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Michal Marek <mmarek@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "brcm80211-dev-list.pdl@...adcom.com" 
        <brcm80211-dev-list.pdl@...adcom.com>,
        "brcm80211-dev-list@...ress.com" <brcm80211-dev-list@...ress.com>,
        "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>,
        "linux-kbuild@...r.kernel.org" <linux-kbuild@...r.kernel.org>,
        Jakub Jelinek <jakub@....gnu.org>,
        Martin Liška <marxin@....gnu.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v4 4/9] em28xx: fix em28xx_dvb_init for KASAN

On Thu, Sep 28, 2017 at 4:30 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Thu, Sep 28, 2017 at 6:09 AM, Andrey Ryabinin
> <aryabinin@...tuozzo.com> wrote:
>> On 09/27/2017 04:26 PM, Arnd Bergmann wrote:
>>> On Tue, Sep 26, 2017 at 9:49 AM, Andrey Ryabinin
>>> <aryabinin@...tuozzo.com> wrote:
>
>>> --- a/include/linux/string.h
>>> +++ b/include/linux/string.h
>>> @@ -227,7 +227,7 @@ static inline const char *kbasename(const char *path)
>>>  #define __FORTIFY_INLINE extern __always_inline __attribute__((gnu_inline))
>>>  #define __RENAME(x) __asm__(#x)
>>>
>>> -void fortify_panic(const char *name) __noreturn __cold;
>>> +void fortify_panic(const char *name) __cold;
>>>  void __read_overflow(void) __compiletime_error("detected read beyond
>>> size of object passed as 1st parameter");
>>>  void __read_overflow2(void) __compiletime_error("detected read beyond
>>> size of object passed as 2nd parameter");
>>>  void __read_overflow3(void) __compiletime_error("detected read beyond
>>> size of object passed as 3rd parameter");
>>>
>>> I don't immediately see why the __noreturn changes the behavior here, any idea?
>>>
>>
>>
>> At first I thought that this somehow might be related to __asan_handle_no_return(). GCC calls it
>> before noreturn function. So I made patch to remove generation of these calls (we don't need them in the kernel anyway)
>> but it didn't help. It must be something else than.
>
> I made a reduced test case yesterday (see http://paste.ubuntu.com/25628030/),
> and it shows the same behavior with and without the sanitizer, it uses 128
> bytes without the noreturn attribute and 480 bytes when its added, the sanitizer
> adds a factor of 1.5x on top. It's possible that I did something wrong while
> reducing, since the original driver file uses very little stack (a few hundred
> bytes) without -fsanitize=kernel-address, but finding out what happens in
> the reduced case may still help understand the other one.

This is now GCC PR82365, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82365

I've come up with a workaround, but I'm not sure if that is any better than the
alternatives, will send the patch as a follow-up in a bit.

     Arnd