linux-kernel - Re: [PATCH v2 01/11] kasan: unify static kasan_flag

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Message-ID: <20250630143934.15284Caf-hca@linux.ibm.com>
Date: Mon, 30 Jun 2025 16:39:34 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Cc: Sabyrzhan Tasbolatov <snovitoll@...il.com>, ryabinin.a.a@...il.com,
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Subject: Re: [PATCH v2 01/11] kasan: unify static kasan_flag_enabled across
 modes

On Mon, Jun 30, 2025 at 02:31:00PM +0200, Alexander Gordeev wrote:
> On Thu, Jun 26, 2025 at 08:31:37PM +0500, Sabyrzhan Tasbolatov wrote:
> 
> Hi Sabyrzhan,
> 
> > diff --git a/mm/kasan/generic.c b/mm/kasan/generic.c
> > index d54e89f8c3e..32c432df24a 100644
> > --- a/mm/kasan/generic.c
> > +++ b/mm/kasan/generic.c
> > @@ -36,6 +36,17 @@
> >  #include "kasan.h"
> >  #include "../slab.h"
> >  
> > +/*
> > + * Initialize Generic KASAN and enable runtime checks.
> > + * This should be called from arch kasan_init() once shadow memory is ready.
> > + */
> > +void __init kasan_init_generic(void)
> > +{
> > +	static_branch_enable(&kasan_flag_enabled);
> 
> s390 crashes at this line, when the whole series is applied.
> 
> FWIW, it looks like kasan is called while its state is not yet finalized.
> E.g. whether calling __asan_report_store4_noabort() before kasan_init_generic()
> is expected?

It crashes because with this conversion a call to static_branch_enable() is
introduced. This one get's called way before jump_label_init() init has been
called. Therefore the STATIC_KEY_CHECK_USE() in static_key_enable_cpuslocked()
triggers.

This again tries to emit a warning. Due to lack of console support that early
the kernel crashes.

One possible solution would be to move the kasan init function to
arch/s390/kernel/setup.c, after jump_label_init() has been called.
If we want this, is a different question.

It seems to work, so I see no reason for not doing that.

Vasily, since you did nearly all of the KASAN work for s390, do you have any
opinion about this?