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Re: Can't find a solution to a failed secure boot kernel loading
From: |
Dimitri John Ledkov |
Subject: |
Re: Can't find a solution to a failed secure boot kernel loading |
Date: |
Tue, 10 May 2022 15:43:18 +0100 |
On Tue, 10 May 2022 at 15:07, Łukasz Piątkowski <piontec@gmail.com> wrote:
>
> What I'm trying to do is to sign a mainline kernel built by ubuntu
> (https://kernel.ubuntu.com/~kernel-ppa/mainline/) with my private key, that
> is already enrolled to MOK, and boot it with Secure Boot.
>
> > the MOK key as generated by Ubuntu/Debian tooling, creates a signing
> > certificate that self-limits itself to only support Kernel Module signing.
>
> OK, that explains why the key in `/var/lib/shim-signed/mok` doesn't work.
> Still, I have created my own key as well (listed below for inspection, it has
> code signing extension), enrolled that key in MOK and signed the ubuntu
> mainline kernel (the kernel I'm trying to boot) with it. The result is
> exactly the same. I was using exactly the same procedure a few ubuntu
> editions back and it was definitely working. From what I learned so far, this
> might be related to the BootHole bug
> (https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-10713) that was
> fixed some time ago.
>
> My generated key is:
>
> root@T495:~/mok# openssl x509 -in MOK.pem -text -noout
> Certificate:
> Data:
> Version: 3 (0x2)
> Serial Number:
> 42:61:86:b2:29:3d:ca:eb:98:87:ae:3d:74:95:c7:f2:63:8f:8a:3b
> Signature Algorithm: sha256WithRSAEncryption
> Issuer: C = PL, ST = Poznan, L = Poznan, O = none, CN = Secure Boot
> Signing, emailAddress = example@example.com
> Validity
> Not Before: Feb 18 19:28:16 2020 GMT
> Not After : Jan 25 19:28:16 2120 GMT
> Subject: C = PL, ST = Poznan, L = Poznan, O = none, CN = Secure Boot
> Signing, emailAddress = example@example.com
> Subject Public Key Info:
> Public Key Algorithm: rsaEncryption
> Public-Key: (2048 bit)
> Modulus: [cut]
> Exponent: 65537 (0x10001)
> X509v3 extensions:
> X509v3 Subject Key Identifier:
> EC:57:4E:BD:DC:1A:CF:B4:55:16:4A:CE:CB:E4:9E:44:5C:C4:63:F6
> X509v3 Authority Key Identifier:
> EC:57:4E:BD:DC:1A:CF:B4:55:16:4A:CE:CB:E4:9E:44:5C:C4:63:F6
> X509v3 Basic Constraints: critical
> CA:FALSE
> X509v3 Extended Key Usage:
> Code Signing, 1.3.6.1.4.1.311.10.3.6, 1.3.6.1.4.1.2312.16.1.2
This is bad... certs that have 1.3.6.1.4.1.2312.16.1.2 cannot be used
to sign kernels.
Your cert must _not_ have 1.3.6.1.4.1.2312.16.1.2 EKU set on it.
You cannot use the same certificate to sign both kernel and modules.
> Netscape Comment:
> OpenSSL Generated Certificate
> Signature Algorithm: sha256WithRSAEncryption
> Signature Value: [cut]
>
> On Tue, May 10, 2022 at 3:26 PM Dimitri John Ledkov
> <dimitri.ledkov@canonical.com> wrote:
>>
>> the MOK key as generated by Ubuntu/Debian tooling, creates a signing
>> certificate that self-limits itself to only support Kernel Module
>> signing.
>> Signatures made by such certificate, are not trusted by shim for the
>> purpose of code signing of bootloaders (i.e. grub) or kernels (i.e.
>> linux).
>> I also responded this on stackoverflow.
>>
>> The automatically generated MOK key is only usable to sign kernel
>> modules, i.e. self-built DKMS modules.
>>
>> --
>> okurrr,
>>
>> Dimitri
>>
>> On Tue, 10 May 2022 at 11:33, Łukasz Piątkowski <piontec@gmail.com> wrote:
>> >
>> > Hi everyone - I'm new here!
>> >
>> > Sorry for going with my problem directly to the grub-devel maling list,
>> > but I'm pretty sure my problem is GRUB related. Still, I've spent some
>> > hours trying to find a solution on the Internet and I failed :( So, here
>> > it comes - if anyone has time to explain my problem to a layman, it would
>> > be awesome. Even better, if you can maybe answer here on stackoverflow,
>> > where it can be easier to find, I believe
>> > (https://unix.stackexchange.com/questions/701612/cant-load-self-signed-kernel-with-secure-boot-on-bad-shim-signature).
>> >
>> > I'm running ubuntu with Secure Boot on. Everything works fine when I use a
>> > kernel that comes packaged from cannonical. Still, I have issues running a
>> > self-signed kernel (this is actually an externally built kernel, that I
>> > have verified and want to use for my own machine). I'm pretty sure my
>> > signature with MOK key is OK (verification below), but still when I try to
>> > boot the kernel from grub, after selecting the correct entry, I get an
>> > error that reads "Loading ... error: bad shim signature." I'm wrapping my
>> > head around it and can't find a solution. Why, even though both kernels
>> > are signed with MOK keys, one of them works and the other doesn't?
>> >
>> > Here's info about kernel signatures:
>> >
>> > root@T495:~# sbsign --key /var/lib/shim-signed/mok/MOK.priv --cert
>> > /var/lib/shim-signed/mok/MOK.pem /boot/vmlinuz
>> > Image was already signed; adding additional signature
>> >
>> > root@T495:~# sbverify --list /boot/vmlinuz
>> > signature 1
>> > image signature issuers:
>> > - /C=PL/ST=Poznan/L=Poznan/O=none/CN=Secure Boot
>> > Signing/emailAddress=example@example.com
>> > image signature certificates:
>> > - subject: /C=PL/ST=yes/L=yes/O=none/CN=Secure Boot
>> > Signing/emailAddress=example@example.com
>> > issuer: /C=PL/ST=yes/L=yes/O=none/CN=Secure Boot
>> > Signing/emailAddress=example@example.com
>> > signature 2
>> > image signature issuers:
>> > - /CN=ubuntu Secure Boot Module Signature key
>> > image signature certificates:
>> > - subject: /CN=ubuntu Secure Boot Module Signature key
>> > issuer: /CN=ubuntu Secure Boot Module Signature key
>> >
>> >
>> > And here about MOK keys:
>> >
>> > root@T495:~# openssl x509 -in /var/lib/shim-signed/mok/MOK.pem
>> > -fingerprint -noout
>> > SHA1
>> > Fingerprint=81:A2:93:CB:06:6F:52:BA:D9:E2:39:68:9D:FA:E2:2B:0C:95:3C:F7
>> > root@T495:~# mokutil --list-enrolled | grep "81:a2:93"
>> > SHA1 Fingerprint:
>> > 81:a2:93:cb:06:6f:52:ba:d9:e2:39:68:9d:fa:e2:2b:0c:95:3c:f7
>> >
>> > If there are any docs that help understand that, I'm happy to be
>> > redirected there :)
>> >
>> > piontec
>> > _______________________________________________
>> > Grub-devel mailing list
>> > Grub-devel@gnu.org
>> > https://lists.gnu.org/mailman/listinfo/grub-devel
>>
>> _______________________________________________
>> Grub-devel mailing list
>> Grub-devel@gnu.org
>> https://lists.gnu.org/mailman/listinfo/grub-devel
>
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