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From: Masahiro Yamada <yamada.masahiro@socionext.com>
To: 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>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
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
Subject: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are not
inlined
Date: Mon, 30 Sep 2019 14:59:25 +0900
Message-Id: <20190930055925.25842-1-yamada.masahiro@socionext.com>
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KernelCI reports that bcm2835_defconfig is no longer booting since
commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
forcibly"):
https://lkml.org/lkml/2019/9/26/825
I also received a regression report from Nicolas Saenz Julienne:
https://lkml.org/lkml/2019/9/27/263
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.
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.
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.
Since that commit, all architectures can enable CONFIG_OPTIMIZE_INLINING.
So, __always_inline is now the only guaranteed way of forcible inlining.
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.
Call uaccess_save_and_enable() before assigning the __p ("r0"), and
uaccess_restore() after evacuating the __e ("r0").
Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_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>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Tested-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
---
arch/arm/include/asm/uaccess.h | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.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 = current_thread_info()->addr_limit - 1; \
+ unsigned int __ua_flags = uaccess_save_and_enable(); \
register typeof(*(p)) __user *__p asm("r0") = (p); \
register __inttype(x) __r2 asm("r2"); \
register unsigned long __l asm("r1") = __limit; \
register int __e asm("r0"); \
- unsigned int __ua_flags = uaccess_save_and_enable(); \
+ unsigned int __err; \
switch (sizeof(*(__p))) { \
case 1: \
if (sizeof((x)) >= 8) \
@@ -223,9 +224,10 @@ extern int __get_user_64t_4(void *);
break; \
default: __e = __get_user_bad(); break; \
} \
- uaccess_restore(__ua_flags); \
+ __err = __e; \
x = (typeof(*(p))) __r2; \
- __e; \
+ uaccess_restore(__ua_flags); \
+ __err; \
})
#define get_user(x, p) \