Re: kexec breaks with 5.4 due to memzero_explicit

[Hans de Goede]

Hi,

On 07-10-2019 15:20, Arvind Sankar wrote:
> On Mon, Oct 07, 2019 at 11:10:18AM +0200, Hans de Goede wrote:
> > Hi,
> >
> > On 07-10-2019 10:50, Hans de Goede wrote:
> > > Hi,
> > >
> > > On 07-10-2019 05:09, Arvind Sankar wrote:
> > > > Hi, arch/x86/purgatory/purgatory.ro has an undefined symbol
> > > > memzero_explicit. This has come from commit 906a4bb97f5d ("crypto:
> > > > sha256 - Use get/put_unaligned_be32 to get input, memzero_explicit")
> > > > according to git bisect.
> > >
> > > Hmm, it (obviously) does build for me and using kexec still also works
> > > for me.
> > >
> > > But it seems that you are right and that this should not build, weird.
> >
> > Ok, I understand now, it seems that the kernel will happily build with
> > undefined symbols in the purgatory and my kexec testing did not hit
> > the sha256 check path (*) so it did not crash. I can reproduce this before my patch:
>
> Yes -- this should really be fixed. purgatory build should fail if there
> are undefined symbols, in fact the Makefile apparently is trying to do
> something to catch undefined references?
>
> LDFLAGS_purgatory.ro := -e purgatory_start -r --no-undefined -nostdlib -z nodefaultlib
>
> This doesn't seem to actually do anything though. Anyone know of a way
> to force ld to error if the resulting object would have undefined
> symbols?

I've figured out a way to get an error for the missing symbol, I will
Cc you on the patch which I will post upstream soon.

I will also write a similar patch for s390 and post that upstream
(untested) separately.

Regards,

Hans