linux-kernel - Re: [PATCH v4 6/9] kasan/um: select ARCH_DEFER_KASAN and call kasan_init

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Message-ID: <CACzwLxhs+Rt9-q6tKi3Kvu7HpZ2VgZAc4XEXZ4MEB60UbFjDKg@mail.gmail.com>
Date: Wed, 6 Aug 2025 09:35:38 +0500
From: Sabyrzhan Tasbolatov <snovitoll@...il.com>
To: Andrey Ryabinin <ryabinin.a.a@...il.com>
Cc: hca@...ux.ibm.com, christophe.leroy@...roup.eu, andreyknvl@...il.com, 
	agordeev@...ux.ibm.com, akpm@...ux-foundation.org, zhangqing@...ngson.cn, 
	chenhuacai@...ngson.cn, trishalfonso@...gle.com, davidgow@...gle.com, 
	glider@...gle.com, dvyukov@...gle.com, kasan-dev@...glegroups.com, 
	linux-kernel@...r.kernel.org, loongarch@...ts.linux.dev, 
	linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org, 
	linux-s390@...r.kernel.org, linux-um@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 6/9] kasan/um: select ARCH_DEFER_KASAN and call kasan_init_generic

On Tue, Aug 5, 2025 at 10:19 PM Andrey Ryabinin <ryabinin.a.a@...il.com> wrote:
>
>
>
> On 8/5/25 4:26 PM, Sabyrzhan Tasbolatov wrote:
> >
> > diff --git a/arch/um/Kconfig b/arch/um/Kconfig
> > index 9083bfdb773..8d14c8fc2cd 100644
> > --- a/arch/um/Kconfig
> > +++ b/arch/um/Kconfig
> > @@ -5,6 +5,7 @@ menu "UML-specific options"
> >  config UML
> >       bool
> >       default y
> > +     select ARCH_DEFER_KASAN
>
> select ARCH_DEFER_KASAN if STATIC_LINK

As pointed out in commit 5b301409e8bc("UML: add support for KASAN
under x86_64"),

: Also note that, while UML supports both KASAN in inline mode
(CONFIG_KASAN_INLINE)
: and static linking (CONFIG_STATIC_LINK), it does not support both at
the same time.

I've tested that for UML,
ARCH_DEFER_KASAN works if STATIC_LINK && KASAN_OUTLINE
ARCH_DEFER_KASAN works if KASAN_INLINE && !STATIC_LINK

ARCH_DEFER_KASAN if STATIC_LINK, and KASAN_INLINE=y by default from defconfig
crashes with SEGFAULT here (I didn't understand what it is, I think
the main() constructors
is not prepared in UML):

 ► 0       0x609d6f87 strlen+43
   1       0x60a20db0 _dl_new_object+48
   2       0x60a24627 _dl_non_dynamic_init+103
   3       0x60a25f9a __libc_init_first+42
   4       0x609eb6b2 __libc_start_main_impl+2434
   5       0x6004a025 _start+37

Since this is the case only for UML, AFAIU, I don't think we want to change
conditions in lib/Kconfig.kasan. Shall I leave UML Kconfig as it is? e.g.

select ARCH_DEFER_KASAN

>
> >       select ARCH_WANTS_DYNAMIC_TASK_STRUCT
> >       select ARCH_HAS_CACHE_LINE_SIZE
> >       select ARCH_HAS_CPU_FINALIZE_INIT
> > diff --git a/arch/um/include/asm/kasan.h b/arch/um/include/asm/kasan.h
> > index f97bb1f7b85..81bcdc0f962 100644
> > --- a/arch/um/include/asm/kasan.h
> > +++ b/arch/um/include/asm/kasan.h
> > @@ -24,11 +24,6 @@
> >
> >  #ifdef CONFIG_KASAN
> >  void kasan_init(void);
> > -extern int kasan_um_is_ready;
> > -
> > -#ifdef CONFIG_STATIC_LINK
> > -#define kasan_arch_is_ready() (kasan_um_is_ready)
> > -#endif
> >  #else
> >  static inline void kasan_init(void) { }
> >  #endif /* CONFIG_KASAN */