linux-kernel - Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAMuHMdW8ndAdGnSHopYFMWvw7wk7wKz_7+N91M1jRHoqK1KBrg@mail.gmail.com>
Date: Thu, 6 Nov 2025 17:20:09 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Yury Norov <yury.norov@...il.com>, Michael Turquette <mturquette@...libre.com>, 
	Stephen Boyd <sboyd@...nel.org>, Nicolas Ferre <nicolas.ferre@...rochip.com>, 
	Alexandre Belloni <alexandre.belloni@...tlin.com>, Claudiu Beznea <claudiu.beznea@...on.dev>, 
	Giovanni Cabiddu <giovanni.cabiddu@...el.com>, Herbert Xu <herbert@...dor.apana.org.au>, 
	David Miller <davem@...emloft.net>, Linus Walleij <linus.walleij@...aro.org>, 
	Bartosz Golaszewski <brgl@...ev.pl>, Joel Stanley <joel@....id.au>, 
	Andrew Jeffery <andrew@...econstruct.com.au>, Crt Mori <cmo@...exis.com>, 
	Jonathan Cameron <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>, Jacky Huang <ychuang3@...oton.com>, 
	Shan-Chun Hung <schung@...oton.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.com>, 
	Johannes Berg <johannes@...solutions.net>, Jakub Kicinski <kuba@...nel.org>, Alex Elder <elder@...e.org>, 
	David Laight <david.laight.linux@...il.com>, Vincent Mailhol <mailhol.vincent@...adoo.fr>, 
	Jason Baron <jbaron@...mai.com>, Borislav Petkov <bp@...en8.de>, Tony Luck <tony.luck@...el.com>, 
	Michael Hennerich <Michael.Hennerich@...log.com>, Kim Seer Paller <kimseer.paller@...log.com>, 
	David Lechner <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, Richard Genoud <richard.genoud@...tlin.com>, 
	Cosmin Tanislav <demonsingur@...il.com>, Biju Das <biju.das.jz@...renesas.com>, 
	Jianping Shen <Jianping.Shen@...bosch.com>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Miquel Raynal <miquel.raynal@...tlin.com>, 
	Richard Weinberger <richard@....at>, Vignesh Raghavendra <vigneshr@...com>, linux-clk@...r.kernel.org, 
	linux-arm-kernel@...ts.infradead.org, linux-renesas-soc@...r.kernel.org, 
	linux-crypto@...r.kernel.org, linux-edac@...r.kernel.org, qat-linux@...el.com, 
	linux-gpio@...r.kernel.org, linux-aspeed@...ts.ozlabs.org, 
	linux-iio@...r.kernel.org, linux-sound@...r.kernel.org, 
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org, 
	Ping-Ke Shih <pkshih@...ltek.com>, linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH v6 12/26] bitfield: Add less-checking __FIELD_{GET,PREP}()

Hi Andy,

On Thu, 6 Nov 2025 at 17:09, Andy Shevchenko
<andriy.shevchenko@...el.com> wrote:
> On Thu, Nov 06, 2025 at 03:49:03PM +0100, Geert Uytterhoeven wrote:
> > On Thu, 6 Nov 2025 at 15:44, Andy Shevchenko
> > <andriy.shevchenko@...el.com> wrote:
> > > On Thu, Nov 06, 2025 at 02:34:00PM +0100, Geert Uytterhoeven wrote:
> > > > The BUILD_BUG_ON_MSG() check against "~0ull" works only with "unsigned
> > > > (long) long" _mask types.  For constant masks, that condition is usually
> > > > met, as GENMASK() yields an UL value.  The few places where the
> > > > constant mask is stored in an intermediate variable were fixed by
> > > > changing the variable type to u64 (see e.g. [1] and [2]).
> > > >
> > > > However, for non-constant masks, smaller unsigned types should be valid,
> > > > too, but currently lead to "result of comparison of constant
> > > > 18446744073709551615 with expression of type ... is always
> > > > false"-warnings with clang and W=1.
> > > >
> > > > Hence refactor the __BF_FIELD_CHECK() helper, and factor out
> > > > __FIELD_{GET,PREP}().  The later lack the single problematic check, but
> > > > are otherwise identical to FIELD_{GET,PREP}(), and are intended to be
> > > > used in the fully non-const variants later.

> > > > +     BUILD_BUG_ON_MSG(__bf_cast_unsigned(mask, mask) >               \
> > > > +                      __bf_cast_unsigned(reg, ~0ull),                \
> > > > +                      pfx "type of reg too small for mask")
> > >
> > > Perhaps we may convert this (and others?) to static_assert():s at some point?
> >
> > Nick tried that before, without success:
> > https://lore.kernel.org/all/CAKwvOdm_prtk1UQNJQGidZm44Lk582S3p=of0y46+rVjnSgXJg@mail.gmail.com
>
> Ah, this is unfortunate.

Of course, it might be an actual bug in the i915 driver...

The extra checking in field_prep() in case the compiler can
determine that the mask is a constant already found a possible bug
in drivers/net/wireless/realtek/rtw89/core.c:rtw89_roc_end():

    rtw89_write32_mask(rtwdev, reg, B_AX_RX_FLTR_CFG_MASK, rtwdev->hal.rx_fltr);

drivers/net/wireless/realtek/rtw89/reg.h:

    #define B_AX_RX_MPDU_MAX_LEN_MASK GENMASK(21, 16)
    #define B_AX_RX_FLTR_CFG_MASK ((u32)~B_AX_RX_MPDU_MAX_LEN_MASK)

so it looks like B_AX_RX_FLTR_CFG_MASK is not the proper mask for
this operation...

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds