Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: Re: kexec breaks with 5.4 due to memzero_explicit
From:   Hans de Goede <hdegoede@redhat.com>
To:     Arvind Sankar <nivedita@alum.mit.edu>, linux-kernel@vger.kernel.org
Cc:     Ingo Molnar <mingo@kernel.org>, x86@kernel.org
References: <20191007030939.GB5270@rani.riverdale.lan>
 <28f3d204-47a2-8b4f-f6a7-11d73c2d87c8@redhat.com>
Message-ID: <0f083019-61e8-7ed5-dde7-99e1aa363d9c@redhat.com>
Date:   Mon, 7 Oct 2019 11:10:18 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.1.1
MIME-Version: 1.0
In-Reply-To: <28f3d204-47a2-8b4f-f6a7-11d73c2d87c8@redhat.com>
Content-Language: en-US
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: quoted-printable
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi,

On 07-10-2019 10:50, Hans de Goede wrote:
> Hi,
>=20
> 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.
>=20
> Hmm, it (obviously) does build for me and using kexec still also works
> for me.
>=20
> 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 000000000040100=
0
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 000000000040100=
0

Regards,

Hans


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