Re: kexec breaks with 5.4 due to memzero_explicit

[Hans de Goede]

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:

[hans@shalem linux]$ ld arch/x86/purgatory/purgatory.ro
ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000
ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
sha256.c:(.text+0x1c0c): undefined reference to `memzero_explicit'

And I can confirm that it is gone after my patch:

[hans@shalem linux]$ ld arch/x86/purgatory/purgatory.ro
ld: warning: cannot find entry symbol _start; defaulting to 0000000000401000

Regards,

Hans


*) I tried with a Fedora signed kernel, dunno how to trigger this if that does not
trigger it