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From:   Fabrizio Castro <fabrizio.castro@bp.renesas.com>
To:     Masahiro Yamada <yamada.masahiro@socionext.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        Russell King <rmk+kernel@armlinux.org.uk>
CC:     Linus Torvalds <torvalds@linux-foundation.org>,
        Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Russell King <linux@armlinux.org.uk>,
        Stefan Agner <stefan@agner.ch>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vincent Whitchurch <vincent.whitchurch@axis.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are
 not inlined
Thread-Topic: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are
 not inlined
Thread-Index: AQHVd1S32ABkM001uEud5so3zUxMOqdEckYg
Date:   Mon, 30 Sep 2019 17:00:52 +0000
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> From: linux-kernel-owner@vger.kernel.org <linux-kernel-owner@vger.kernel.=
org> On Behalf Of Masahiro Yamada
> Sent: 30 September 2019 06:59
> Subject: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are =
not inlined
>=20
> KernelCI reports that bcm2835_defconfig is no longer booting since
> commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
> forcibly"):
>=20
>   https://lkml.org/lkml/2019/9/26/825
>=20
> I also received a regression report from Nicolas Saenz Julienne:
>=20
>   https://lkml.org/lkml/2019/9/27/263
>=20
> This problem has cropped up on arch/arm/config/bcm2835_defconfig
> because it enables CONFIG_CC_OPTIMIZE_FOR_SIZE. The compiler tends
> to prefer not inlining functions with -Os. I was able to reproduce
> it with other boards and defconfig files by manually enabling
> CONFIG_CC_OPTIMIZE_FOR_SIZE.
>=20
> The __get_user_check() specifically uses r0, r1, r2 registers.
> So, uaccess_save_and_enable() and uaccess_restore() must be inlined
> in order to avoid those registers being overwritten in the callees.
>=20
> Prior to commit 9012d011660e ("compiler: allow all arches to enable
> CONFIG_OPTIMIZE_INLINING"), the 'inline' marker was always enough for
> inlining functions, except on x86.
>=20
> Since that commit, all architectures can enable CONFIG_OPTIMIZE_INLINING.
> So, __always_inline is now the only guaranteed way of forcible inlining.
>=20
> I want to keep as much compiler's freedom as possible about the inlining
> decision. So, I changed the function call order instead of adding
> __always_inline around.
>=20
> Call uaccess_save_and_enable() before assigning the __p ("r0"), and
> uaccess_restore() after evacuating the __e ("r0").
>=20
> Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZ=
E_INLINING")
> Reported-by: "kernelci.org bot" <bot@kernelci.org>
> Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Tested-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>

> ---
>=20
>  arch/arm/include/asm/uaccess.h | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>=20
> diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uacces=
s.h
> index 303248e5b990..559f252d7e3c 100644
> --- a/arch/arm/include/asm/uaccess.h
> +++ b/arch/arm/include/asm/uaccess.h
> @@ -191,11 +191,12 @@ extern int __get_user_64t_4(void *);
>  #define __get_user_check(x, p)						\
>  	({								\
>  		unsigned long __limit =3D current_thread_info()->addr_limit - 1; \
> +		unsigned int __ua_flags =3D uaccess_save_and_enable();	\
>  		register typeof(*(p)) __user *__p asm("r0") =3D (p);	\
>  		register __inttype(x) __r2 asm("r2");			\
>  		register unsigned long __l asm("r1") =3D __limit;		\
>  		register int __e asm("r0");				\
> -		unsigned int __ua_flags =3D uaccess_save_and_enable();	\
> +		unsigned int __err;					\
>  		switch (sizeof(*(__p))) {				\
>  		case 1:							\
>  			if (sizeof((x)) >=3D 8)				\
> @@ -223,9 +224,10 @@ extern int __get_user_64t_4(void *);
>  			break;						\
>  		default: __e =3D __get_user_bad(); break;			\
>  		}							\
> -		uaccess_restore(__ua_flags);				\
> +		__err =3D __e;						\
>  		x =3D (typeof(*(p))) __r2;				\
> -		__e;							\
> +		uaccess_restore(__ua_flags);				\
> +		__err;							\
>  	})
>=20
>  #define get_user(x, p)							\
> --
> 2.17.1