linux-hardening - [PATCH v6 8/8] ARM: make get_current() and __my_cpu_offset() __always

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Date:   Tue, 25 Jan 2022 10:14:53 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux@...linux.org.uk, linux-arm-kernel@...ts.infradead.org
Cc:     linux-hardening@...r.kernel.org, Ard Biesheuvel <ardb@...nel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Kees Cook <keescook@...omium.org>,
        Keith Packard <keithpac@...zon.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Marc Zyngier <maz@...nel.org>
Subject: [PATCH v6 8/8] ARM: make get_current() and __my_cpu_offset() __always_inline

The get_current() and __my_cpu_offset() accessors evaluate to only a
single instruction emitted inline, but due to the size of the asm string
that is created for SMP+v6 configurations, the compiler assumes
otherwise, and may emit the functions out of line instead.

So use __always_inline to avoid this.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 arch/arm/include/asm/current.h | 2 +-
 arch/arm/include/asm/percpu.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/current.h b/arch/arm/include/asm/current.h
index 131a89bbec6b..1e1178bf176d 100644
--- a/arch/arm/include/asm/current.h
+++ b/arch/arm/include/asm/current.h
@@ -14,7 +14,7 @@ struct task_struct;
 
 extern struct task_struct *__current;
 
-static inline __attribute_const__ struct task_struct *get_current(void)
+static __always_inline __attribute_const__ struct task_struct *get_current(void)
 {
 	struct task_struct *cur;
 
diff --git a/arch/arm/include/asm/percpu.h b/arch/arm/include/asm/percpu.h
index a09034ae45a1..7545c87c251f 100644
--- a/arch/arm/include/asm/percpu.h
+++ b/arch/arm/include/asm/percpu.h
@@ -25,7 +25,7 @@ static inline void set_my_cpu_offset(unsigned long off)
 	asm volatile("mcr p15, 0, %0, c13, c0, 4" : : "r" (off) : "memory");
 }
 
-static inline unsigned long __my_cpu_offset(void)
+static __always_inline unsigned long __my_cpu_offset(void)
 {
 	unsigned long off;
 
-- 
2.30.2