Re: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] Missing KMSAN attributes on the `extern` declarations of `arch_local_save_flags` and `arch_local_irq_save` will cause spurious use-of-uninitialized-value reports.
--

--- Patch [1]: [PATCH] s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN ---
commit 75ac5ab83800e65155075aeee91b3fd23aa6274d
Author: Ilya Leoshkevich <iii@linux.ibm.com>

s390/irqflags: add out-of-line definitions of arch_local_irq_*() for KMSAN

This commit moves KMSAN arch_local_irq_*() definitions out-of-line to avoid
warnings about static functions in inline functions. Uninstrumented
decompressor code keeps the inline definitions, while non-GPL modules see
the out-of-line versions.

Closes: https://lore.kernel.org/oe-kbuild-all/202607131219.euJHPSJ5-lkp@intel.com/

> diff --git a/arch/s390/include/asm/irqflags.h b/arch/s390/include/asm/irqflags.h
> index bcab456dfb803..44d158f7831e6 100644
> --- a/arch/s390/include/asm/irqflags.h
> +++ b/arch/s390/include/asm/irqflags.h
> @@ -37,18 +37,24 @@ static __always_inline void __arch_local_irq_ssm(unsigned long flags)
>  	asm volatile("ssm   %0" : : "Q" (flags) : "memory");
>  }
>  
> -#ifdef CONFIG_KMSAN
> -#define arch_local_irq_attributes noinline notrace __no_sanitize_memory __maybe_unused
> +#if defined(CONFIG_KMSAN) && !defined(__DECOMPRESSOR)
> +extern unsigned long arch_local_save_flags(void);
> +extern unsigned long arch_local_irq_save(void);

[Severity: High]
Since these extern declarations lack KMSAN attributes, will instrumented
callers expect a populated return value shadow in __msan_retval_tls?

When arch_local_save_flags() and arch_local_irq_save() are called from
instrumented code, the caller reads __msan_retval_tls. However, because the
corresponding definitions are marked noinstr:

arch/s390/kernel/irqflags.c:
noinstr unsigned long arch_local_save_flags(void)
{
	return __arch_local_save_flags();
}

instrumentation is skipped, and __msan_retval_tls is never populated before
returning to the caller. 

Could this result in spurious use-of-uninitialized-value reports on every
IRQ state check or lock operation (like spin_lock_irqsave) when the kernel
is built with CONFIG_KMSAN?

> +extern void arch_local_irq_enable_external(void);
> +extern void arch_local_irq_enable(void);
>  #else
> -#define arch_local_irq_attributes __always_inline
> +#define arch_local_save_flags __arch_local_save_flags
> +#define arch_local_irq_save __arch_local_irq_save

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260806100038.3163298-1-iii@linux.ibm.com?part=1