linux-kernel - Re: [PATCH v8 3/4] arm64: kexec_file: use more system keyrings to verify kernel image signature

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Date:   Thu, 09 Jun 2022 19:15:27 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Coiby Xu <coxu@...hat.com>, kexec@...ts.infradead.org
Cc:     linux-arm-kernel@...ts.infradead.org,
        Michal Suchanek <msuchanek@...e.de>,
        Baoquan He <bhe@...hat.com>, Dave Young <dyoung@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Chun-Yi Lee <jlee@...e.com>, stable@...r.kernel.org,
        keyrings@...r.kernel.org, linux-security-module@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v8 3/4] arm64: kexec_file: use more system keyrings to
 verify kernel image signature

On Thu, 2022-05-12 at 15:01 +0800, Coiby Xu wrote:
> Currently, a problem faced by arm64 is if a kernel image is signed by a
> MOK key, loading it via the kexec_file_load() system call would be
> rejected with the error "Lockdown: kexec: kexec of unsigned images is
> restricted; see man kernel_lockdown.7".
> 
> This happens because image_verify_sig uses only the primary keyring that
> contains only kernel built-in keys to verify the kexec image.

>From the git history it's clear that .platform keyring was upstreamed
during the same open window as commit 732b7b93d849 ("arm64: kexec_file:
add kernel signature verification support").   Loading the MOK keys
onto the .platform keyring was upstreamed much later.  For this reason,
commit 732b7b93d849 only used keys on the  .builtin_trusted_keys
keyring.   This patch is now addressing it and the newly upstreamed
.machine keyring.

Only using the .builtin_trusted_keys is the problem statement, which
should be one of the first lines of the patch description, if not the
first line.

> 
> This patch allows to verify arm64 kernel image signature using not only
> .builtin_trusted_keys but also .platform and .secondary_trusted_keys
> keyring.

Please remember to update this to include the .machine keyring.

> 
> Fixes: 732b7b93d849 ("arm64: kexec_file: add kernel signature verification support")

Since the MOK keys weren't loaded onto the .platform keyring until much
later, I would not classify this as a fix.

thanks,

Mimi