linux-kernel - Re: [PATCH 1/2] carl9170: re-fix fortified-memset warning

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Date:   Fri, 23 Jun 2023 18:05:57 +0200
From:   "Arnd Bergmann" <arnd@...db.de>
To:     "Christian Lamparter" <chunkeey@...il.com>,
        "Arnd Bergmann" <arnd@...nel.org>, "Kalle Valo" <kvalo@...nel.org>,
        "Kees Cook" <keescook@...omium.org>,
        "Johannes Berg" <johannes.berg@...el.com>,
        "Shiji Yang" <yangshiji66@...look.com>,
        "Nick Kossifidis" <mickflemm@...il.com>,
        "Jiri Slaby" <jirislaby@...nel.org>,
        "Christian Marangi" <ansuelsmth@...il.com>
Cc:     linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] carl9170: re-fix fortified-memset warning

On Fri, Jun 23, 2023, at 17:38, Christian Lamparter wrote:
> On 6/23/23 17:23, Arnd Bergmann wrote:
>
> Wait! I want to point out this funny thing is happening in ath too!
>
> https://lore.kernel.org/linux-wireless/TYAP286MB03154F9AAFD4C35BEEDE4A99BC4CA@TYAP286MB0315.JPNP286.PROD.OUTLOOK.COM/T/#mf1b8919a000fe661803c17073f48b3c410888541
>
> And that patch got NACK by Jiri Slaby because like me he suspects that
> this is a compiler bug.

FWIW, that is one I don't see with clang-17 or gcc-13. The one I'm addressing
here is the only thing I see in ath wireless with the default set of
warning options, though this driver does have a couple of others that
are unrelated, when you enable the source data check in memcpy() by
building with W=1.

 In file included from  drivers/net/wireless/ath/ath9k/xmit.c:17:
In file included from  include/linux/dma-mapping.h:7:
In file included from include/linux/string.h:254:
/home/arnd/arm-soc/include/linux/fortify-string.h:592:4: error: call to '__read_overflow2_field' declared with 'warning' attribute: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __read_overflow2_field(q_size_field, size);
                        ^
include/linux/fortify-string.h:592:4: error: call to '__read_overflow2_field' declared with 'warning' attribute: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
2 errors generated.
/home/arnd/arm-soc/include/linux/fortify-string.h:592:4: error: call to '__read_overflow2_field' declared with 'warning' attribute: detected read beyond size of field (2nd parameter); maybe use struct_group()? [-Werror,-Wattribute-warning]
                        __read_overflow2_field(q_size_field, size);

> so, what's going wrong with fortified there?

Kees might have a better answer to that, my best guess is that
the one I'm addressing stems from the confusion between different
union members.

Doing the randconfig builds with the latest compilers, carl9170 is the
only one I see with fortified-string warnings, and there are a few
dozen other drivers that I see with W=1, including one that affects
all wireless drivers.

     Arnd