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From patchwork Mon Sep 30 05:59:25 2019
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X-Patchwork-Submitter: Masahiro Yamada <yamada.masahiro@socionext.com>
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X-Patchwork-Id: 1132459
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From: Masahiro Yamada <yamada.masahiro@socionext.com>
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To: linux-arm-kernel@lists.infradead.org,
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        Russell King <rmk+kernel@armlinux.org.uk>
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Cc: Linus Torvalds <torvalds@linux-foundation.org>,
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        Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
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        Nick Desaulniers <ndesaulniers@google.com>,
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        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
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        Masahiro Yamada <yamada.masahiro@socionext.com>,
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        Julien Thierry <julien.thierry.kdev@gmail.com>,
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        Russell King <linux@armlinux.org.uk>,
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        Stefan Agner <stefan@agner.ch>,
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        Thomas Gleixner <tglx@linutronix.de>,
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        Vincent Whitchurch <vincent.whitchurch@axis.com>,
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        linux-kernel@vger.kernel.org
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Subject: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are not
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 inlined
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Date: Mon, 30 Sep 2019 14:59:25 +0900
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Message-Id: <20190930055925.25842-1-yamada.masahiro@socionext.com>
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X-Mailer: git-send-email 2.17.1
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Precedence: bulk
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List-ID: <linux-kernel.vger.kernel.org>
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KernelCI reports that bcm2835_defconfig is no longer booting since
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commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING
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forcibly"):
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  https://lkml.org/lkml/2019/9/26/825
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I also received a regression report from Nicolas Saenz Julienne:
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  https://lkml.org/lkml/2019/9/27/263
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This problem has cropped up on arch/arm/config/bcm2835_defconfig
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because it enables CONFIG_CC_OPTIMIZE_FOR_SIZE. The compiler tends
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to prefer not inlining functions with -Os. I was able to reproduce
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it with other boards and defconfig files by manually enabling
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CONFIG_CC_OPTIMIZE_FOR_SIZE.
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The __get_user_check() specifically uses r0, r1, r2 registers.
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So, uaccess_save_and_enable() and uaccess_restore() must be inlined
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in order to avoid those registers being overwritten in the callees.
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Prior to commit 9012d011660e ("compiler: allow all arches to enable
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CONFIG_OPTIMIZE_INLINING"), the 'inline' marker was always enough for
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inlining functions, except on x86.
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Since that commit, all architectures can enable CONFIG_OPTIMIZE_INLINING.
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So, __always_inline is now the only guaranteed way of forcible inlining.
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I want to keep as much compiler's freedom as possible about the inlining
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decision. So, I changed the function call order instead of adding
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__always_inline around.
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Call uaccess_save_and_enable() before assigning the __p ("r0"), and
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uaccess_restore() after evacuating the __e ("r0").
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Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")
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Reported-by: "kernelci.org bot" <bot@kernelci.org>
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Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
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Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
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Acked-by: Arnd Bergmann <arnd@arndb.de>
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Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
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Tested-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>
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Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
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---
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 arch/arm/include/asm/uaccess.h | 8 +++++---
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 1 file changed, 5 insertions(+), 3 deletions(-)
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diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
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index 303248e5b990..559f252d7e3c 100644
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--- a/arch/arm/include/asm/uaccess.h
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+++ b/arch/arm/include/asm/uaccess.h
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@@ -191,11 +191,12 @@ extern int __get_user_64t_4(void *);
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 #define __get_user_check(x, p)						\
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 	({								\
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 		unsigned long __limit = current_thread_info()->addr_limit - 1; \
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+		unsigned int __ua_flags = uaccess_save_and_enable();	\
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 		register typeof(*(p)) __user *__p asm("r0") = (p);	\
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 		register __inttype(x) __r2 asm("r2");			\
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 		register unsigned long __l asm("r1") = __limit;		\
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 		register int __e asm("r0");				\
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-		unsigned int __ua_flags = uaccess_save_and_enable();	\
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+		unsigned int __err;					\
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 		switch (sizeof(*(__p))) {				\
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 		case 1:							\
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 			if (sizeof((x)) >= 8)				\
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@@ -223,9 +224,10 @@ extern int __get_user_64t_4(void *);
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 			break;						\
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 		default: __e = __get_user_bad(); break;			\
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 		}							\
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-		uaccess_restore(__ua_flags);				\
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+		__err = __e;						\
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 		x = (typeof(*(p))) __r2;				\
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-		__e;							\
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+		uaccess_restore(__ua_flags);				\
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+		__err;							\
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 	})
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 #define get_user(x, p)							\