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

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Date:   Wed, 23 Feb 2022 22:05:03 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Chris Zankel <chris@...kel.net>
Cc:     Kees Cook <keescook@...omium.org>,
        Max Filippov <jcmvbkbc@...il.com>,
        Marc Zyngier <maz@...nel.org>, linux-xtensa@...ux-xtensa.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH] xtensa: 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: Chris Zankel <chris@...kel.net>
Cc: Max Filippov <jcmvbkbc@...il.com>
Cc: Marc Zyngier <maz@...nel.org>
Cc: linux-xtensa@...ux-xtensa.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 arch/xtensa/Kconfig                  | 1 +
 arch/xtensa/include/asm/current.h    | 2 ++
 arch/xtensa/include/asm/stacktrace.h | 2 +-
 arch/xtensa/kernel/irq.c             | 3 +--
 4 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/xtensa/Kconfig b/arch/xtensa/Kconfig
index 8ac599aa6d99..887432327613 100644
--- a/arch/xtensa/Kconfig
+++ b/arch/xtensa/Kconfig
@@ -3,6 +3,7 @@ config XTENSA
 	def_bool y
 	select ARCH_32BIT_OFF_T
 	select ARCH_HAS_BINFMT_FLAT if !MMU
+	select ARCH_HAS_CURRENT_STACK_POINTER
 	select ARCH_HAS_DMA_PREP_COHERENT if MMU
 	select ARCH_HAS_SYNC_DMA_FOR_CPU if MMU
 	select ARCH_HAS_SYNC_DMA_FOR_DEVICE if MMU
diff --git a/arch/xtensa/include/asm/current.h b/arch/xtensa/include/asm/current.h
index 5d98a7ad4251..08010dbf5e09 100644
--- a/arch/xtensa/include/asm/current.h
+++ b/arch/xtensa/include/asm/current.h
@@ -26,6 +26,8 @@ static inline struct task_struct *get_current(void)
 
 #define current get_current()
 
+register unsigned long current_stack_pointer __asm__("a1");
+
 #else
 
 #define GET_CURRENT(reg,sp)		\
diff --git a/arch/xtensa/include/asm/stacktrace.h b/arch/xtensa/include/asm/stacktrace.h
index fe06e8ed162b..4d84fd6bd43c 100644
--- a/arch/xtensa/include/asm/stacktrace.h
+++ b/arch/xtensa/include/asm/stacktrace.h
@@ -22,7 +22,7 @@ static __always_inline unsigned long *stack_pointer(struct task_struct *task)
 	unsigned long *sp;
 
 	if (!task || task == current)
-		__asm__ __volatile__ ("mov %0, a1\n" : "=a"(sp));
+		sp = current_stack_pointer;
 	else
 		sp = (unsigned long *)task->thread.sp;
 
diff --git a/arch/xtensa/kernel/irq.c b/arch/xtensa/kernel/irq.c
index 15051a8a1539..529fe9245821 100644
--- a/arch/xtensa/kernel/irq.c
+++ b/arch/xtensa/kernel/irq.c
@@ -36,9 +36,8 @@ asmlinkage void do_IRQ(int hwirq, struct pt_regs *regs)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 	/* Debugging check for stack overflow: is there less than 1KB free? */
 	{
-		unsigned long sp;
+		unsigned long sp = current_stack_pointer;
 
-		__asm__ __volatile__ ("mov %0, a1\n" : "=a" (sp));
 		sp &= THREAD_SIZE - 1;
 
 		if (unlikely(sp < (sizeof(thread_info) + 1024)))
-- 
2.30.2