Re: [PATCH v4 6/9] kasan/um: select ARCH_DEFER_KASAN and call kasan_init_generic

[Andrey Ryabinin <ryabinin.a.a@gmail.com>]

On 8/6/25 6:35 AM, Sabyrzhan Tasbolatov wrote:
> On Tue, Aug 5, 2025 at 10:19 PM Andrey Ryabinin <ryabinin.a.a@gmail.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
> 

No surprise here, kasan_arch_is_ready() or ARCH_DEFER_KASAN doesn't work with KASAN_INLINE=y
This configuration combination (STATIC_LINK + KASAN_INLINE) wasn't possible before:

#ifndef kasan_arch_is_ready
static inline bool kasan_arch_is_ready(void)   { return true; }
#elif !defined(CONFIG_KASAN_GENERIC) || !defined(CONFIG_KASAN_OUTLINE)
#error kasan_arch_is_ready only works in KASAN generic outline mode!
#endif



> 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
> 

No, this should have if STATIC_LINK