linux-kernel - [PATCH] ARM: add __always_inline to functions called from __get_user

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Message-Id: <20191002102802.29691-1-yamada.masahiro@socionext.com>
Date:   Wed,  2 Oct 2019 19:28:02 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     patches@....linux.org.uk
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Russell King <rmk+kernel@...linux.org.uk>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Enrico Weigelt <info@...ux.net>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Stefan Agner <stefan@...er.ch>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>
Subject: [PATCH] ARM: add __always_inline to functions called from __get_user_check()

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 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.
Otherwise, those register assignments would be entirely dropped,
according to my analysis of the disassembly.

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 added __always_inline to 4 functions in the call-graph from the
__get_user_check() macro.

Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")
Reported-by: "kernelci.org bot" <bot@...nelci.org>
Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
---

KernelVersion: v5.4-rc1

 arch/arm/include/asm/domain.h  | 8 ++++----
 arch/arm/include/asm/uaccess.h | 4 ++--
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm/include/asm/domain.h b/arch/arm/include/asm/domain.h
index 567dbede4785..f1d0a7807cd0 100644
--- a/arch/arm/include/asm/domain.h
+++ b/arch/arm/include/asm/domain.h
@@ -82,7 +82,7 @@
 #ifndef __ASSEMBLY__
 
 #ifdef CONFIG_CPU_CP15_MMU
-static inline unsigned int get_domain(void)
+static __always_inline unsigned int get_domain(void)
 {
 	unsigned int domain;
 
@@ -94,7 +94,7 @@ static inline unsigned int get_domain(void)
 	return domain;
 }
 
-static inline void set_domain(unsigned val)
+static __always_inline void set_domain(unsigned int val)
 {
 	asm volatile(
 	"mcr	p15, 0, %0, c3, c0	@ set domain"
@@ -102,12 +102,12 @@ static inline void set_domain(unsigned val)
 	isb();
 }
 #else
-static inline unsigned int get_domain(void)
+static __always_inline unsigned int get_domain(void)
 {
 	return 0;
 }
 
-static inline void set_domain(unsigned val)
+static __always_inline void set_domain(unsigned int val)
 {
 }
 #endif
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 303248e5b990..98c6b91be4a8 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -22,7 +22,7 @@
  * perform such accesses (eg, via list poison values) which could then
  * be exploited for priviledge escalation.
  */
-static inline unsigned int uaccess_save_and_enable(void)
+static __always_inline unsigned int uaccess_save_and_enable(void)
 {
 #ifdef CONFIG_CPU_SW_DOMAIN_PAN
 	unsigned int old_domain = get_domain();
@@ -37,7 +37,7 @@ static inline unsigned int uaccess_save_and_enable(void)
 #endif
 }
 
-static inline void uaccess_restore(unsigned int flags)
+static __always_inline void uaccess_restore(unsigned int flags)
 {
 #ifdef CONFIG_CPU_SW_DOMAIN_PAN
 	/* Restore the user access mask */
-- 
2.17.1