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From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Borislav Petkov <bp@alien8.de>, Joe Perches <joe@perches.com>,
	Johannes Berg <johannes@sipsolutions.net>,
	Kees Cook <keescook@chromium.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Ingo Molnar <mingo@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Geert Uytterhoeven <geert@linux-m68k.org>,
	Haren Myneni <haren@us.ibm.com>
Subject: Re: [Patch v4 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs
Date: Thu, 10 Oct 2019 11:24:23 +0900	[thread overview]
Message-ID: <CAK7LNARmYFxoWJqkSO+Fd9PkxoisU3ri=yULjvb6_XsZzh07hg@mail.gmail.com> (raw)
In-Reply-To: <20191009214502.637875-3-rikard.falkeborn@gmail.com>

On Thu, Oct 10, 2019 at 6:45 AM Rikard Falkeborn
<rikard.falkeborn@gmail.com> wrote:
>
> GENMASK() and GENMASK_ULL() are supposed to be called with the high bit
> as the first argument and the low bit as the second argument. Mixing
> them will return a mask with zero bits set.
>
> Recent commits show getting this wrong is not uncommon, see e.g.
> commit aa4c0c9091b0 ("net: stmmac: Fix misuses of GENMASK macro") and
> commit 9bdd7bb3a844 ("clocksource/drivers/npcm: Fix misuse of GENMASK
> macro").
>
> To prevent such mistakes from appearing again, add compile time sanity
> checking to the arguments of GENMASK() and GENMASK_ULL(). If both
> arguments are known at compile time, and the low bit is higher than the
> high bit, break the build to detect the mistake immediately.
>
> Since GENMASK() is used in declarations, BUILD_BUG_ON_ZERO() must be
> used instead of BUILD_BUG_ON().
>
> __builtin_constant_p does not evaluate is argument, it only checks if it
> is a constant or not at compile time, and __builtin_choose_expr does not
> evaluate the expression that is not chosen. Therefore, GENMASK(x++, 0)
> does only evaluate x++ once.
>
> Commit 95b980d62d52 ("linux/bits.h: make BIT(), GENMASK(), and friends
> available in assembly") made the macros in linux/bits.h available in
> assembly. Since BUILD_BUG_OR_ZERO() is not asm compatible, disable the
> checks if the file is included in an asm file.
>
> Due to bugs in GCC versions before 4.9 [0], disable the check if
> building with a too old GCC compiler.
>
> [0]: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=19449
>
> Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>

Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>



> ---
> Geert, can you check if this works better? I do not have gcc 4.6-4.8
> readily installed.
>
> Kees, Masahiro, since I changed this patch, I didn't include your
> reviewed-by tags.
>
> Changes in v4:
>   - Disable the argument check for GCC < 4.9 due to a compiler bug.
> Changes in v3:
>   - Changed back to shorter macro argument names
>   - Remove casts and use 0 instead of UL(0) in GENMASK_INPUT_CHECK(),
>     since all results in GENMASK_INPUT_CHECK() are now ints. Update
>     commit message to reflect that.
>
> Changes in v2:
>   - Add comment about why inputs are not checked when used in asm file
>   - Use UL(0) instead of 0
>   - Extract mask creation in a separate macro to improve readability
>   - Use high and low instead of h and l (part of this was extracted to a
>     separate patch)
>   - Updated commit message
>
> Joe Perches sent a series to fix the existing misuses of GENMASK().
> Those patches have been merged into Linus tree except two places where
> the GENMASK misuse is in unused macros, which will not fail to build.
> There was also a patch by Nathan Chancellor that have now been merged.
>
>  include/linux/bits.h | 22 ++++++++++++++++++++--
>  1 file changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/bits.h b/include/linux/bits.h
> index 669d69441a62..f108302a3121 100644
> --- a/include/linux/bits.h
> +++ b/include/linux/bits.h
> @@ -18,12 +18,30 @@
>   * position @h. For example
>   * GENMASK_ULL(39, 21) gives us the 64bit vector 0x000000ffffe00000.
>   */
> -#define GENMASK(h, l) \
> +#if !defined(__ASSEMBLY__) && \
> +       (!defined(CONFIG_CC_IS_GCC) || CONFIG_GCC_VERSION >= 49000)
> +#include <linux/build_bug.h>
> +#define GENMASK_INPUT_CHECK(h, l) \
> +       (BUILD_BUG_ON_ZERO(__builtin_choose_expr( \
> +               __builtin_constant_p((l) > (h)), (l) > (h), 0)))
> +#else
> +/*
> + * BUILD_BUG_ON_ZERO is not available in h files included from asm files,
> + * disable the input check if that is the case.
> + */
> +#define GENMASK_INPUT_CHECK(h, l) 0
> +#endif
> +
> +#define __GENMASK(h, l) \
>         (((~UL(0)) - (UL(1) << (l)) + 1) & \
>          (~UL(0) >> (BITS_PER_LONG - 1 - (h))))
> +#define GENMASK(h, l) \
> +       (GENMASK_INPUT_CHECK(h, l) + __GENMASK(h, l))
>
> -#define GENMASK_ULL(h, l) \
> +#define __GENMASK_ULL(h, l) \
>         (((~ULL(0)) - (ULL(1) << (l)) + 1) & \
>          (~ULL(0) >> (BITS_PER_LONG_LONG - 1 - (h))))
> +#define GENMASK_ULL(h, l) \
> +       (GENMASK_INPUT_CHECK(h, l) + __GENMASK_ULL(h, l))
>
>  #endif /* __LINUX_BITS_H */
> --
> 2.23.0
>


-- 
Best Regards
Masahiro Yamada

  reply	other threads:[~2019-10-10  2:25 UTC|newest]

Thread overview: 109+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20190710050444epcas1p250f7aa0f8798a7757df51d66f5970c2a@epcas1p2.samsung.com>
2019-07-10  5:04 ` [PATCH 00/12] treewide: Fix GENMASK misuses Joe Perches
2019-07-10  5:04   ` [PATCH 01/12] checkpatch: Add GENMASK tests Joe Perches
2019-07-24 18:03     ` Joe Perches
2019-07-10  5:04   ` [PATCH 02/12] clocksource/drivers/npcm: Fix misuse of GENMASK macro Joe Perches
2019-07-10  9:10     ` [tip:timers/urgent] " tip-bot for Joe Perches
2019-07-15 10:00     ` [PATCH 02/12] " Avi Fishman
2019-07-10  5:04   ` [PATCH 03/12] drm: aspeed_gfx: " Joe Perches
2019-07-24 17:16     ` Joe Perches
2019-07-25  1:10       ` Andrew Jeffery
2019-07-25  1:18         ` Joe Perches
2019-07-25  2:52           ` Joel Stanley
2019-07-25 14:37             ` Joe Perches
2019-07-10  5:04   ` [PATCH 04/12] iio: adc: max9611: " Joe Perches
2019-07-14 11:54     ` Jonathan Cameron
2019-07-14 12:19       ` Joe Perches
2019-07-14 14:37         ` Jacopo Mondi
2019-07-29 21:52         ` Jacopo Mondi
2019-07-31  8:37           ` Jonathan Cameron
2019-07-10  5:04   ` [PATCH 05/12] irqchip/gic-v3-its: " Joe Perches
2019-07-10  8:28     ` Marc Zyngier
2019-07-10  9:07     ` [tip:irq/urgent] " tip-bot for Joe Perches
2019-07-10  5:04   ` [PATCH 06/12] mmc: meson-mx-sdio: " Joe Perches
2019-07-22  7:23     ` Neil Armstrong
2019-07-22 13:43     ` Ulf Hansson
2019-07-10  5:04   ` [PATCH 07/12] net: ethernet: mediatek: Fix misuses " Joe Perches
2019-07-10  5:04   ` [PATCH 08/12] net: stmmac: " Joe Perches
2019-07-10 10:33     ` Jose Abreu
2019-07-10  5:04   ` [PATCH 09/12] rtw88: Fix misuse " Joe Perches
2019-07-10  5:07     ` Tony Chuang
2019-07-24 11:48     ` Kalle Valo
2019-07-10  5:04   ` [PATCH 10/12] phy: amlogic: G12A: " Joe Perches
2019-07-22  7:23     ` Neil Armstrong
2019-08-23  2:41       ` Kishon Vijay Abraham I
2019-08-23  4:59         ` Joe Perches
2019-07-10  5:04   ` [PATCH 11/12] staging: media: cedrus: " Joe Perches
2019-07-10  7:23     ` Paul Kocialkowski
2019-07-24 17:09     ` Joe Perches
2019-07-24 18:35       ` Greg Kroah-Hartman
2019-07-24 18:39         ` Joe Perches
2019-07-24 18:55           ` Greg Kroah-Hartman
2019-07-25  6:46       ` Hans Verkuil
2019-07-10  5:04   ` [PATCH 12/12] ASoC: wcd9335: " Joe Perches
2019-07-22 12:22     ` Applied "ASoC: wcd9335: Fix misuse of GENMASK macro" to the asoc tree Mark Brown
2019-07-10  9:17   ` [PATCH 00/12] treewide: Fix GENMASK misuses Johannes Berg
2019-07-10  9:43     ` Russell King - ARM Linux admin
2019-07-10 15:45       ` Joe Perches
2019-07-10 16:01         ` Joe Perches
2019-07-27 19:54           ` Rikard Falkeborn
2019-07-28 23:45             ` Joe Perches
2019-07-31 19:03               ` [PATCH] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-07-31 19:27                 ` Joe Perches
2019-08-01 23:03                   ` Rikard Falkeborn
2019-08-02  1:40                   ` Masahiro Yamada
2019-08-02  3:13                     ` Joe Perches
2019-08-02  3:25                       ` Masahiro Yamada
2019-08-02 18:18                         ` Rikard Falkeborn
2019-08-03  3:03                           ` Masahiro Yamada
2019-08-03  3:12                             ` Masahiro Yamada
2019-08-03 18:36                               ` Rikard Falkeborn
2019-08-04  6:45                                 ` Masahiro Yamada
2019-08-05 19:55                                   ` Rikard Falkeborn
2019-08-06 15:19                                     ` Masahiro Yamada
2019-08-06 19:27                                       ` Rikard Falkeborn
2019-08-06 21:15                                         ` Joe Perches
2019-08-07 20:53                                           ` Rikard Falkeborn
2019-08-01  2:50                 ` Masahiro Yamada
2019-08-01  2:57                   ` Joe Perches
2019-08-01 23:03                     ` Rikard Falkeborn
2019-08-01 23:03                 ` [PATCH v2 1/2] linux/bits.h: Clarify macro argument names Rikard Falkeborn
2019-08-01 23:03                   ` [PATCH v2 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-08-01 23:14                     ` Joe Perches
2019-08-07 14:27                     ` Guenter Roeck
2019-08-07 14:55                       ` Masahiro Yamada
2019-08-07 16:52                         ` Guenter Roeck
2019-08-07 20:07                           ` Rikard Falkeborn
2019-08-08  0:07                         ` Joe Perches
2019-08-08  0:58                           ` Guenter Roeck
2019-08-08  1:08                             ` Joe Perches
2019-08-08  1:53                               ` Guenter Roeck
2019-08-08  2:44                     ` kbuild test robot
2019-08-08  2:44                     ` kbuild test robot
2019-08-08  3:46                   ` [PATCH v2 1/2] linux/bits.h: Clarify macro argument names Masahiro Yamada
2019-08-10 18:43                     ` Rikard Falkeborn
2019-08-10 19:20                     ` Joe Perches
2019-08-11 18:49                   ` [PATCH v3 0/3] Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-08-11 18:49                     ` [PATCH v3 1/3] x86/boot: Use common BUILD_BUG_ON Rikard Falkeborn
2019-08-12 18:19                       ` [tip:x86/boot] " tip-bot for Rikard Falkeborn
2019-08-16 12:19                       ` tip-bot for Rikard Falkeborn
2019-08-11 18:49                     ` [PATCH v3 2/3] linux/build_bug.h: Change type to int Rikard Falkeborn
2019-10-06  2:26                       ` Masahiro Yamada
2019-08-11 18:49                     ` [PATCH v3 3/3] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-10-06  2:30                       ` Masahiro Yamada
2019-10-08  7:23                       ` Geert Uytterhoeven
2019-10-08  7:44                         ` Masahiro Yamada
2019-10-08  7:52                           ` Masahiro Yamada
2019-10-08 19:06                             ` Rikard Falkeborn
2019-08-12 17:58                     ` [PATCH v3 0/3] " Kees Cook
2019-10-05 19:46                     ` Rikard Falkeborn
2019-10-09 21:45                     ` [Patch v4 0/2] " Rikard Falkeborn
2019-10-09 21:45                       ` [Patch v4 1/2] linux/build_bug.h: Change type to int Rikard Falkeborn
2019-10-09 21:45                       ` [Patch v4 2/2] linux/bits.h: Add compile time sanity check of GENMASK inputs Rikard Falkeborn
2019-10-10  2:24                         ` Masahiro Yamada [this message]
2019-10-12  2:27                         ` Andrew Morton
2019-10-22 19:53                           ` Rikard Falkeborn
2019-11-01 21:28                             ` Rikard Falkeborn
2020-03-08 19:39                               ` [PATCH v5] " Rikard Falkeborn
2020-03-09 16:40                                 ` Kees Cook
2019-07-11 21:30   ` [PATCH 00/12] treewide: Fix GENMASK misuses David Miller
2019-07-12 12:54   ` Andrzej Hajda

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