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

[Guenter Roeck]

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@xxxxxxxxxxxx> 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/175/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

> -Kees
> 
> >
> > Guenter
> >
> > ---
> > # bad: [4dfc2788033d30dfccfd4268e06dd73ce2c654ed] Merge tag 'iommu-updates-v4.14' of git://git.kernel.org/pub/scm/linux/kernel/git/joro/iommu
> > # good: [5969d1bb3082b41eba8fd2c826559abe38ccb6df] Merge branch 'gperf-removal'
> > git bisect start 'HEAD' '5969d1bb3082'
> > # bad: [fbd01410e89a66f346ba1b3c0161e1198449b746] Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
> > git bisect bad fbd01410e89a66f346ba1b3c0161e1198449b746
> > # good: [0d519f2d1ed1f11e49abc88cfcf6cf13b83ba14c] Merge tag 'pci-v4.14-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci
> > git bisect good 0d519f2d1ed1f11e49abc88cfcf6cf13b83ba14c
> > # bad: [229cf16d3c8ac2e9b082c223fd0e619dc8f62cc1] sh: defconfig: cleanup from old Kconfig options
> > git bisect bad 229cf16d3c8ac2e9b082c223fd0e619dc8f62cc1
> > # good: [1caffba9db4aa27c3e7ebc05668afca1f991ab8d] drivers/scsi/sym53c8xx_2/sym_hipd.c: convert to use memset32
> > git bisect good 1caffba9db4aa27c3e7ebc05668afca1f991ab8d
> > # good: [7c61bd6983b185272315722787cceacf5f5d2e7d] lib/cmdline.c: remove meaningless comment
> > git bisect good 7c61bd6983b185272315722787cceacf5f5d2e7d
> > # bad: [718b303b49893d8f9dd469f710d76f77673bd35d] autofs: use AUTOFS_DEV_IOCTL_SIZE
> > git bisect bad 718b303b49893d8f9dd469f710d76f77673bd35d
> > # good: [9367bb730e4d9d85a8911a08a3542ec2aa873d37] binfmt_flat: delete two error messages for a failed memory allocation in decompress_exec()
> > git bisect good 9367bb730e4d9d85a8911a08a3542ec2aa873d37
> > # bad: [e54c7bcbf14a25dc3a913b4c808b52121c522e9b] autofs: make disc device user accessible
> > git bisect bad e54c7bcbf14a25dc3a913b4c808b52121c522e9b
> > # bad: [33d72f3822d7ff8a9e45bd7413c811085cb87aa5] init/main.c: extract early boot entropy from the passed cmdline
> > git bisect bad 33d72f3822d7ff8a9e45bd7413c811085cb87aa5
> > # good: [121388a31362b0d3176dc1190ac8064b98a61b20] init: move stack canary initialization after setup_arch
> > git bisect good 121388a31362b0d3176dc1190ac8064b98a61b20
> > # first bad commit: [33d72f3822d7ff8a9e45bd7413c811085cb87aa5] init/main.c: extract early boot entropy from the passed cmdline
> 
> 
> 
> -- 
> Kees Cook
> Pixel Security