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Subject: Re: kexec breaks with 5.4 due to memzero_explicit
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Arvind Sankar <nivedita@alum.mit.edu>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        Borislav Petkov <bp@alien8.de>,
        Thomas Gleixner <tglx@linutronix.de>
References: <20191007030939.GB5270@rani.riverdale.lan>
 <28f3d204-47a2-8b4f-f6a7-11d73c2d87c8@redhat.com>
 <0f083019-61e8-7ed5-dde7-99e1aa363d9c@redhat.com>
 <20191007130942.GA82950@gmail.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <a485ad7f-ad7b-00e1-910b-e4ab3fe07cd2@redhat.com>
Date:   Mon, 7 Oct 2019 16:07:11 +0200
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Hi,

On 07-10-2019 15:09, Ingo Molnar wrote:
>=20
> * Hans de Goede <hdegoede@redhat.com> wrote:
>=20
>> 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 befo=
re my patch:
>>
>> [hans@shalem linux]$ ld arch/x86/purgatory/purgatory.ro
>> ld: warning: cannot find entry symbol _start; defaulting to 000000000040=
1000
>> ld: arch/x86/purgatory/purgatory.ro: in function `sha256_transform':
>> sha256.c:(.text+0x1c0c): undefined reference to `memzero_explicit'
>=20
> I've applied your fix,=20

I already answered this bit.

> but would it make sense to also integrate this
> linker test in the regular build with a second patch, to make sure
> something similar doesn't occur again?

But I forgot to answer this part, yes I will look into making the build
fail as soon as we have the fix for this in place for 5.4 .

Regards,

Hans