linux-kernel - Re: kexec breaks with 5.4 due to memzero

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Date:   Mon, 7 Oct 2019 11:10:18 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Arvind Sankar <nivedita@...m.mit.edu>, linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>, x86@...nel.org
Subject: Re: kexec breaks with 5.4 due to memzero_explicit

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@...lem 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@...lem 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