Re: [Xen-devel] [PATCH for-4.9 v2] xen/livepatch: Don't crash on encountering STN_UNDEF relocations

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Thu, Jun 22, 2017 at 11:27:50AM -0400, Konrad Rzeszutek Wilk wrote:
> On Wed, Jun 21, 2017 at 09:26:15PM -0400, Konrad Rzeszutek Wilk wrote:
> > On Wed, Jun 21, 2017 at 07:13:36PM +0100, Andrew Cooper wrote:
> > > A symndx of STN_UNDEF is special, and means a symbol value of 0.  While
> > > legitimate in the ELF standard, its existance in a livepatch is 
> > > questionable
> > > at best.  Until a plausible usecase presents itself, reject such a 
> > > relocation
> > > with -EOPNOTSUPP.
> > > 
> > > Additionally, perform a safety check on elf->sym[symndx].sym before
> > > derefencing it, to avoid tripping over a NULL pointer when calculating 
> > > val.
> > > 
> > > Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> > 
> > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> [x86 right now, 
> > will do
> > arm32 tomorrow]
> 
> I did that on my Cubietruck and I made the rookie mistake of not trying
> a hypervisor _without_ your changes, so I don't know if this crash
> (see inline) is due to your patch or something else.
> 
> Also I messed up and made the livepatch test run every time it boots, so
> now it is stuck in a loop of crashes :-(
> 
> The git tree is:
> 
> git://xenbits.xen.org/people/konradwilk/xen.git staging-4.9
> 
> Stay tuned.

And I see the same thing with b38b147 (that is the top of 'origin/staging').

So time to dig in.

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