[PATCH v2] MIPS: Only use current_stack_pointer on GCC

[PATCH v2] MIPS: Only use current_stack_pointer on GCC

[Kees Cook]

Unfortunately, Clang did not have support for "sp" as a global register
definition, and was crashing after the addition of current_stack_pointer.
This has been fixed in Clang 15, but earlier Clang versions need to
avoid this code, so add a versioned test and revert back to the
open-coded asm instances. Fixes Clang build error:

fatal error: error in backend: Invalid register name global variable

Fixes: 200ed341b864 ("mips: Implement "current_stack_pointer"")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/lkml/YikTQRql+il3HbrK@dev-arch.thelio-3990X
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Yanteng Si <siyanteng01@gmail.com>
Cc: linux-mips@vger.kernel.org
Signed-off-by: Kees Cook <keescook@chromium.org>
---
v1: https://lore.kernel.org/lkml/20220309204537.390428-1-keescook@chromium.org
v2: - adjust Clang version (Nathan)
---
 arch/mips/Kconfig                   | 2 +-
 arch/mips/include/asm/thread_info.h | 2 ++
 arch/mips/kernel/irq.c              | 3 ++-
 arch/mips/lib/uncached.c            | 4 +++-
 4 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
index 3f58b45fc953..0dae5f1e61cc 100644
--- a/arch/mips/Kconfig
+++ b/arch/mips/Kconfig
@@ -4,7 +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_CURRENT_STACK_POINTER if !CC_IS_CLANG || CLANG_VERSION >= 140000
 	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 4463348d2372..ecae7470faa4 100644
--- a/arch/mips/include/asm/thread_info.h
+++ b/arch/mips/include/asm/thread_info.h
@@ -69,7 +69,9 @@ static inline struct thread_info *current_thread_info(void)
 	return __current_thread_info;
 }
 
+#ifdef CONFIG_ARCH_HAS_CURRENT_STACK_POINTER
 register unsigned long current_stack_pointer __asm__("sp");
+#endif
 
 #endif /* !__ASSEMBLY__ */
 
diff --git a/arch/mips/kernel/irq.c b/arch/mips/kernel/irq.c
index fc313c49a417..5e11582fe308 100644
--- a/arch/mips/kernel/irq.c
+++ b/arch/mips/kernel/irq.c
@@ -75,8 +75,9 @@ void __init init_IRQ(void)
 #ifdef CONFIG_DEBUG_STACKOVERFLOW
 static inline void check_stack_overflow(void)
 {
-	unsigned long sp = current_stack_pointer;
+	unsigned long sp;
 
+	__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 f8d4ca046c3e..f80a67c092b6 100644
--- a/arch/mips/lib/uncached.c
+++ b/arch/mips/lib/uncached.c
@@ -40,7 +40,9 @@ unsigned long run_uncached(void *func)
 	register long ret __asm__("$2");
 	long lfunc = (long)func, ufunc;
 	long usp;
-	long sp = current_stack_pointer;
+	long sp;
+
+	__asm__("move %0, $sp" : "=r" (sp));
 
 	if (sp >= (long)CKSEG0 && sp < (long)CKSEG2)
 		usp = CKSEG1ADDR(sp);
-- 
2.32.0

RE: [PATCH v2] MIPS: Only use current_stack_pointer on GCC

[David Laight]

From: Kees Cook
> Sent: 09 March 2022 22:10
> 
> Unfortunately, Clang did not have support for "sp" as a global register
> definition, and was crashing after the addition of current_stack_pointer.
> This has been fixed in Clang 15, but earlier Clang versions need to
                               ^^ 14
> avoid this code, so add a versioned test and revert back to the
> open-coded asm instances. Fixes Clang build error:
> 
> fatal error: error in backend: Invalid register name global variable

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)

Re: [PATCH v2] MIPS: Only use current_stack_pointer on GCC

[Nick Desaulniers]

On Wed, Mar 9, 2022 at 2:44 PM David Laight <David.Laight@aculab.com> wrote:
>
> From: Kees Cook
> > Sent: 09 March 2022 22:10
> >
> > Unfortunately, Clang did not have support for "sp" as a global register
> > definition, and was crashing after the addition of current_stack_pointer.
> > This has been fixed in Clang 15, but earlier Clang versions need to
>                                ^^ 14

Yeah, with that fixed:
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

Once clang-14 is the minimally supported version, we can go back to
removing the inline asm for everyone.


> > avoid this code, so add a versioned test and revert back to the
> > open-coded asm instances. Fixes Clang build error:
> >
> > fatal error: error in backend: Invalid register name global variable
>
>         David
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>


-- 
Thanks,
~Nick Desaulniers

Re: [PATCH v2] MIPS: Only use current_stack_pointer on GCC

[Thomas Bogendoerfer]

On Wed, Mar 09, 2022 at 02:09:39PM -0800, Kees Cook wrote:
> Unfortunately, Clang did not have support for "sp" as a global register
> definition, and was crashing after the addition of current_stack_pointer.
> This has been fixed in Clang 15, but earlier Clang versions need to
> avoid this code, so add a versioned test and revert back to the
> open-coded asm instances. Fixes Clang build error:
> 
> fatal error: error in backend: Invalid register name global variable
> 
> Fixes: 200ed341b864 ("mips: Implement "current_stack_pointer"")
> Reported-by: Nathan Chancellor <nathan@kernel.org>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> Link: https://lore.kernel.org/lkml/YikTQRql+il3HbrK@dev-arch.thelio-3990X
> Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Guenter Roeck <linux@roeck-us.net>
> Cc: Yanteng Si <siyanteng01@gmail.com>
> Cc: linux-mips@vger.kernel.org
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> v1: https://lore.kernel.org/lkml/20220309204537.390428-1-keescook@chromium.org
> v2: - adjust Clang version (Nathan)
> ---
>  arch/mips/Kconfig                   | 2 +-
>  arch/mips/include/asm/thread_info.h | 2 ++
>  arch/mips/kernel/irq.c              | 3 ++-
>  arch/mips/lib/uncached.c            | 4 +++-
>  4 files changed, 8 insertions(+), 3 deletions(-)

applied to mips-next with the Clang version in the decscription fixed.

Thomas.

-- 
Crap can work. Given enough thrust pigs will fly, but it's not necessarily a
good idea.                                                [ RFC1925, 2.3 ]

Re: [PATCH v2] MIPS: Only use current_stack_pointer on GCC

[Kees Cook]

On Mon, Mar 14, 2022 at 03:52:15PM +0100, Thomas Bogendoerfer wrote:
> On Wed, Mar 09, 2022 at 02:09:39PM -0800, Kees Cook wrote:
> > Unfortunately, Clang did not have support for "sp" as a global register
> > definition, and was crashing after the addition of current_stack_pointer.
> > This has been fixed in Clang 15, but earlier Clang versions need to
> > avoid this code, so add a versioned test and revert back to the
> > open-coded asm instances. Fixes Clang build error:
> > 
> > fatal error: error in backend: Invalid register name global variable
> > 
> > Fixes: 200ed341b864 ("mips: Implement "current_stack_pointer"")
> > Reported-by: Nathan Chancellor <nathan@kernel.org>
> > Reviewed-by: Nathan Chancellor <nathan@kernel.org>
> > Link: https://lore.kernel.org/lkml/YikTQRql+il3HbrK@dev-arch.thelio-3990X
> > Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
> > Cc: Marc Zyngier <maz@kernel.org>
> > Cc: Guenter Roeck <linux@roeck-us.net>
> > Cc: Yanteng Si <siyanteng01@gmail.com>
> > Cc: linux-mips@vger.kernel.org
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > v1: https://lore.kernel.org/lkml/20220309204537.390428-1-keescook@chromium.org
> > v2: - adjust Clang version (Nathan)
> > ---
> >  arch/mips/Kconfig                   | 2 +-
> >  arch/mips/include/asm/thread_info.h | 2 ++
> >  arch/mips/kernel/irq.c              | 3 ++-
> >  arch/mips/lib/uncached.c            | 4 +++-
> >  4 files changed, 8 insertions(+), 3 deletions(-)
> 
> applied to mips-next with the Clang version in the decscription fixed.

Excellent; thanks very much!

-Kees

-- 
Kees Cook