linux-hardening - [PATCH] mips: Implement "current_stack

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Date:   Wed, 23 Feb 2022 22:04:32 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc:     Kees Cook <keescook@...omium.org>, Marc Zyngier <maz@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Mark Rutland <mark.rutland@....com>,
        Yanteng Si <siyanteng01@...il.com>, linux-mips@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] mips: Implement "current_stack_pointer"

To follow the existing per-arch conventions replace open-coded uses
of asm "sp" as "current_stack_pointer". This will let it be used in
non-arch places (like HARDENED_USERCOPY).

Cc: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
Cc: Marc Zyngier <maz@...nel.org>
Cc: Guenter Roeck <linux@...ck-us.net>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Yanteng Si <siyanteng01@...il.com>
Cc: linux-mips@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/mips/Kconfig                   | 1 +
 arch/mips/include/asm/thread_info.h | 2 ++
 arch/mips/kernel/irq.c              | 3 +--
 arch/mips/lib/uncached.c            | 4 +---
 4 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 058446f01487..6781f87e2218 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -4,6 +4,7 @@ config MIPS
 	default y
 	select ARCH_32BIT_OFF_T if !64BIT
 	select ARCH_BINFMT_ELF_STATE if MIPS_FP_SUPPORT
+	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_DEBUG_VIRTUAL if !64BIT
 	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_KCOV
diff --git a/arch/mips/include/asm/thread_info.h b/arch/mips/include/asm/thread_info.h
index 0b17aaa9e012..4463348d2372 100644
--- a/arch/mips/include/asm/thread_info.h
+++ b/arch/mips/include/asm/thread_info.h
@@ -69,6 +69,8 @@ static inline struct thread_info *current_thread_info(void)
 	return __current_thread_info;
 }
 
+register unsigned long current_stack_pointer __asm__("sp");
+
 #endif /* !__ASSEMBLY__ */
 
 /* thread information allocation */
diff --git a/arch/mips/kernel/irq.c b/arch/mips/kernel/irq.c
index 5e11582fe308..fc313c49a417 100644
--- a/arch/mips/kernel/irq.c
+++ b/arch/mips/kernel/irq.c
@@ -75,9 +75,8 @@ void __init init_IRQ(void)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 static inline void check_stack_overflow(void)
 {
-	unsigned long sp;
+	unsigned long sp = current_stack_pointer;
 
-	__asm__ __volatile__("move %0, $sp" : "=r" (sp));
 	sp &= THREAD_MASK;
 
 	/*
diff --git a/arch/mips/lib/uncached.c b/arch/mips/lib/uncached.c
index f80a67c092b6..f8d4ca046c3e 100644
--- a/arch/mips/lib/uncached.c
+++ b/arch/mips/lib/uncached.c
@@ -40,9 +40,7 @@ unsigned long run_uncached(void *func)
 	register long ret __asm__("$2");
 	long lfunc = (long)func, ufunc;
 	long usp;
-	long sp;
-
-	__asm__("move %0, $sp" : "=r" (sp));
+	long sp = current_stack_pointer;
 
 	if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
 		usp = CKSEG1ADDR(sp);
-- 
2.30.2