linux-kernel - Re: drivers/of: crash on boot

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Date:	Thu, 19 May 2016 09:20:47 -0500
From:	Rob Herring <robh@...nel.org>
To:	Rhyland Klein <rklein@...dia.com>
Cc:	Sasha Levin <sasha.levin@...cle.com>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: drivers/of: crash on boot

On Wed, May 18, 2016 at 8:51 PM, Rob Herring <robh@...nel.org> wrote:
> On Wed, May 18, 2016 at 7:23 PM, Rob Herring <robh@...nel.org> wrote:
>> On Wed, May 18, 2016 at 4:26 PM, Rhyland Klein <rklein@...dia.com> wrote:
>>> On 5/18/2016 3:58 PM, Rhyland Klein wrote:
>>>> On 5/18/2016 3:36 PM, Rob Herring wrote:
>>>>> On Wed, May 18, 2016 at 10:34 AM, Sasha Levin <sasha.levin@...cle.com> wrote:
>>>>>> Hi Rhyland,
>>>>>>
>>>>>> I'm seeing a crash on boot that seems to have been caused by
>>>>>> "drivers/of: Fix depth when unflattening devicetree":
>>>>>>
>>>>>> [   61.145229] ==================================================================
>>>>>>
>>>>>> [   61.147588] BUG: KASAN: stack-out-of-bounds in unflatten_dt_nodes+0x11d2/0x1290 at addr ffff88005b30777c
>
> [...]
>
>>> This patch seems to work for me. I found a bug in my original patch.
>>> Sasha/Rob, can you see if this works for you too:
>>>
>>> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
>>> index 0b5850027bb5..e7a8caac5b27 100644
>>> --- a/drivers/of/fdt.c
>>> +++ b/drivers/of/fdt.c
>>> @@ -407,9 +407,9 @@ static int unflatten_dt_nodes(const void *blob,
>>>
>>>         root = dad;
>>>         fpsizes[depth] = dad ? strlen(of_node_full_name(dad)) : 0;
>>> -       nps[depth+1] = dad;
>>> +       nps[depth] = dad;
>>>         for (offset = 0;
>>> -            offset >= 0;
>>> +            offset >= 0 && depth >= 0;
>>>              offset = fdt_next_node(blob, offset, &depth)) {
>>>                 if (WARN_ON_ONCE(depth >= FDT_MAX_DEPTH))
>>>                         continue;
>>
>> This is not work for me. I'm booting x86 with the DT unit test and
>> KASAN enabled. I suspect our differences are due to different data
>> after the end of the dtb. Also, I think there may be a bug in
>> fdt_next_node FDT_END handling. The "!depth" seems suspicious to me
>> and I think it should be "!(*depth)".

I take that back. Your change does work for me. Must have had something stale.

>> The DT overlay unit tests are also failing. Not sure if that's related.
>
> Seems with the above patch and the fix to fdt_next_node, the problem
> is fixed both for KASAN and the DT overlay tests. Trying it out now
> with some other configurations.

fdt_next_node is in fact correct. Changing it caused failures in the
dtc unit tests.

So I have squashed the above fix into your original fix and pushed
that out to -next. kernelci.org is also seeing some failures due to
this. I'll give this another day or so before sending to Linus.

Rob