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

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Message-ID: <aGKr4DgJ4w3TfJm1@li-008a6a4c-3549-11b2-a85c-c5cc2836eea2.ibm.com>
Date: Mon, 30 Jun 2025 17:23:12 +0200
From: Alexander Gordeev <agordeev@...ux.ibm.com>
To: Heiko Carstens <hca@...ux.ibm.com>
Cc: Vasily Gorbik <gor@...ux.ibm.com>,
        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 04:39:34PM +0200, Heiko Carstens wrote:
> > > +/*
> > > + * 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.

IIRC, we wanted to have kasan coverage as early as possible.
Delaying it past jump_label_init() leaves out pretty big chunk of code?

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