Re: Can't find a solution to a failed secure boot kernel loading

[Dimitri John Ledkov <dimitri.ledkov@canonical.com>]

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
>>
>> _______________________________________________
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>
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