linux-kernel - Re: nios2 crash due to 'init/main.c: extract early boot entropy from the passed cmdline'

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Date:   Mon, 11 Sep 2017 14:25:51 -0400
From:   Daniel Micay <danielmicay@...il.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Kees Cook <keescook@...omium.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ley Foon Tan <lftan@...era.com>,
        nios2-dev@...ts.rocketboards.org,
        Laura Abbott <labbott@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: nios2 crash due to 'init/main.c: extract early boot entropy
 from the passed cmdline'

On Mon, 2017-09-11 at 10:35 -0700, Guenter Roeck wrote:
> On Mon, Sep 11, 2017 at 09:36:00AM -0700, Kees Cook wrote:
> > On Sat, Sep 9, 2017 at 8:58 PM, Guenter Roeck <linux@...ck-us.net>
> > wrote:
> > > Hi,
> > > 
> > > I noticed that nios2 images crash in mainline. Bisect points to
> > > commit
> > > 33d72f3822d7 ("init/main.c: extract early boot entropy from the
> > > passed
> > > cmdline").  Bisect log is attached.
> > > 
> > > As far as I can see, the problem is seen because
> > > add_device_randomness()
> > > calls random_get_entropy(). However, the underlying timer function
> > > used by the nios2 architecture (nios2_timer_read) is not yet
> > > initialized,
> > > causing a NULL pointer access and crash. A sample crash log is at
> > >         http://kerneltests.org/builders/qemu-nios2-master/builds/1
> > > 75/steps/qemubuildcommand/logs/stdio
> > 
> > Oh, yikes. Do you have a full call trace? (Does this come through
> > get_cycles() or via the It seems like we could either initialize the
> > timer earlier or allow it to fall back when not initialized...
> > 
> 
> nios2 doesn't give me a traceback. I followed it by adding debug
> messages.
> The code path is through get_cycles().
> 
> On nios2:
> 
> static u64 nios2_timer_read(struct clocksource *cs)
> {
> 	struct nios2_clocksource *nios2_cs = to_nios2_clksource(cs);
> 	unsigned long flags;
> 	u32 count;
> 
> 	local_irq_save(flags);
> 	count = read_timersnapshot(&nios2_cs->timer);	// <- not
> initialized
> 	local_irq_restore(flags);
> 
> 	/* Counter is counting down */
> 	return ~count;
> }
> 
> cycles_t get_cycles(void)
> {
>         return nios2_timer_read(&nios2_cs.cs);
> }
> EXPORT_SYMBOL(get_cycles);
> 
> Guenter

Maybe it should WARN and return 0 for now if that's NULL?