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

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Thu, Jun 22, 2017 at 12:10:46PM -0400, Konrad Rzeszutek Wilk wrote:
> 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@citrix.com>
> > > 
> > > Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> > > Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> [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.

/me blushes.

I compiled the hypervisor and the livepatches on a cross compiler.
arm-linux-gnueabi-gcc (Ubuntu/Linaro 5.4.0-6ubuntu1~16.04.4) 5.4.0 20160609


But if I compile both on the Cubietruck (natively) it all works nicely.
gcc (Ubuntu/Linaro 4.8.2-19ubuntu1) 4.8.2

So:

Tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> [x86, arm32]

for both of the patches. Sorry for the alarm.

Julien, would you be OK with these two going in 4.9? Please?

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