linux-kernel - Re: [PATCH v3 12/19] firmware_loader: Use security_post_load

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Message-ID: <1595847465.4841.63.camel@kernel.org>
Date:   Mon, 27 Jul 2020 06:57:45 -0400
From:   Mimi Zohar <zohar@...nel.org>
To:     Kees Cook <keescook@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Scott Branden <scott.branden@...adcom.com>,
        Luis Chamberlain <mcgrof@...nel.org>,
        Jessica Yu <jeyu@...nel.org>, SeongJae Park <sjpark@...zon.de>,
        KP Singh <kpsingh@...omium.org>, linux-efi@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-integrity@...r.kernel.org, selinux@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 12/19] firmware_loader: Use security_post_load_data()

On Fri, 2020-07-24 at 14:36 -0700, Kees Cook wrote:
> Now that security_post_load_data() is wired up, use it instead
> of the NULL file argument style of security_post_read_file(),
> and update the security_kernel_load_data() call to indicate that a
> security_kernel_post_load_data() call is expected.
> 
> Wire up the IMA check to match earlier logic. Perhaps a generalized
> change to ima_post_load_data() might look something like this:
> 
>     return process_buffer_measurement(buf, size,
>                                       kernel_load_data_id_str(load_id),
>                                       read_idmap[load_id] ?: FILE_CHECK,
>                                       0, NULL);
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

process_measurement() measures, verifies a file signature -  both
signatures stored as an xattr and as an appended buffer signature -
and augments audit records with the file hash. (Support for measuring,
augmenting audit records, and/or verifying fs-verity signatures has
yet to be added.)

As explained in my response to 11/19, the file descriptor provides the
file pathname associated with the buffer data.  In addition, IMA
policy rules may be defined in terms of other file descriptor info -
uid, euid, uuid, etc.

Recently support was added for measuring the kexec boot command line,
certificates being loaded onto a keyring, and blacklisted file hashes
(limited to appended signatures).  None of these buffers are signed.
 process_buffer_measurement() was added for this reason and as a
result is limited to just measuring the buffer data.

Whether process_measurement() or process_buffer_measurement() should
be modified, needs to be determined.  In either case to support the
init_module syscall, would at minimum require the associated file
pathname.

Mimi