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From: Mimi Zohar <zohar@linux.ibm.com>
To: Kees Cook <keescook@chromium.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Scott Branden <scott.branden@broadcom.com>,
	Luis Chamberlain <mcgrof@kernel.org>,
	Jessica Yu <jeyu@kernel.org>, SeongJae Park <sjpark@amazon.de>,
	KP Singh <kpsingh@chromium.org>,
	linux-efi@vger.kernel.org, linux-security-module@vger.kernel.org,
	linux-integrity@vger.kernel.org, selinux@vger.kernel.org,
	linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 12/19] firmware_loader: Use security_post_load_data()
Date: Wed, 29 Jul 2020 14:10:18 -0400
Message-ID: <e6f7ce4aa506ff016dde9a75c607849587c1ca2c.camel@linux.ibm.com> (raw)
In-Reply-To: <e5ed8876b9907315c2a906ab248639ea8c6d2cd5.camel@linux.ibm.com>

On Wed, 2020-07-29 at 12:29 -0400, Mimi Zohar wrote:
> On Tue, 2020-07-28 at 12:43 -0700, Kees Cook wrote:
> > On Mon, Jul 27, 2020 at 06:57:45AM -0400, Mimi Zohar wrote:
> > > 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@chromium.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.
> > 
> > Right -- I don't intend to make changes to the init_module() syscall
> > since it's deprecated, so this hook is more of a "fuller LSM coverage
> > for old syscalls" addition.
> > 
> > IMA can happily continue to ignore it, which is what I have here, but I
> > thought I'd at least show what it *might* look like. Perhaps BPF LSM is
> > a better example.
> > 
> > Does anything need to change for this patch?
> 
> I wasn't aware that init_syscall was deprecated.  From your original comments,
> it sounded like you wanted a new LSM for verifying kernel module signatures,
> as
> they're currently supported via init_module().
> 
> I was mistaken.  Without a file descriptor, security_post_load_data() will
> measure the firmware, as Scott confirmed, but won't be able to verify the
> signature, whether he signed it using evmctl or not,

Actually, the partial firmware read should be calling
security_kernel_read_file().  The sysfs firmware fallback is calling
security_kernel_load_data().  Which firmware is calling
security_kernel_post_load_data()?

thanks,

Mimi


  reply index

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-24 21:36 [PATCH v3 00/19] Introduce partial kernel_read_file() support Kees Cook
2020-07-24 21:36 ` [PATCH v3 01/19] test_firmware: Test platform fw loading on non-EFI systems Kees Cook
2020-07-24 21:36 ` [PATCH v3 02/19] selftest/firmware: Add selftest timeout in settings Kees Cook
2020-07-24 21:36 ` [PATCH v3 03/19] firmware_loader: EFI firmware loader must handle pre-allocated buffer Kees Cook
2020-07-25 10:07   ` Greg Kroah-Hartman
2020-07-25 15:50     ` Kees Cook
2020-07-25 17:20       ` Greg Kroah-Hartman
2020-07-24 21:36 ` [PATCH v3 04/19] fs/kernel_read_file: Remove FIRMWARE_PREALLOC_BUFFER enum Kees Cook
2020-07-27 13:35   ` Mimi Zohar
2020-07-24 21:36 ` [PATCH v3 05/19] fs/kernel_read_file: Remove FIRMWARE_EFI_EMBEDDED enum Kees Cook
2020-07-24 21:36 ` [PATCH v3 06/19] fs/kernel_read_file: Split into separate include file Kees Cook
2020-07-27 14:41   ` Mimi Zohar
2020-07-24 21:36 ` [PATCH v3 07/19] fs/kernel_read_file: Split into separate source file Kees Cook
2020-07-27 14:53   ` Mimi Zohar
2020-07-24 21:36 ` [PATCH v3 08/19] fs/kernel_read_file: Remove redundant size argument Kees Cook
2020-07-27 16:29   ` Mimi Zohar
2020-07-24 21:36 ` [PATCH v3 09/19] fs/kernel_read_file: Switch buffer size arg to size_t Kees Cook
2020-07-27 16:29   ` Mimi Zohar
2020-07-24 21:36 ` [PATCH v3 10/19] fs/kernel_read_file: Add file_size output argument Kees Cook
2020-07-27 16:29   ` Mimi Zohar
2020-07-24 21:36 ` [PATCH v3 11/19] LSM: Introduce kernel_post_load_data() hook Kees Cook
2020-07-27 10:49   ` Mimi Zohar
2020-07-28 19:41     ` Kees Cook
2020-07-24 21:36 ` [PATCH v3 12/19] firmware_loader: Use security_post_load_data() Kees Cook
2020-07-27 10:57   ` Mimi Zohar
2020-07-28 19:43     ` Kees Cook
2020-07-29 16:29       ` Mimi Zohar
2020-07-29 18:10         ` Mimi Zohar [this message]
2020-07-29 19:13           ` Kees Cook
2020-07-24 21:36 ` [PATCH v3 13/19] module: Call security_kernel_post_load_data() Kees Cook
2020-07-24 21:36 ` [PATCH v3 14/19] LSM: Add "contents" flag to kernel_read_file hook Kees Cook
2020-07-24 21:36 ` [PATCH v3 15/19] IMA: Add support for file reads without contents Kees Cook
2020-07-27 13:23   ` Mimi Zohar
2020-07-28 19:44     ` Kees Cook
2020-07-28 19:56       ` Greg Kroah-Hartman
2020-07-28 20:12         ` Kees Cook
2020-07-24 21:36 ` [PATCH v3 16/19] fs/kernel_file_read: Add "offset" arg for partial reads Kees Cook
2020-07-24 21:36 ` [PATCH v3 17/19] firmware: Store opt_flags in fw_priv Kees Cook
2020-07-24 21:36 ` [PATCH v3 18/19] firmware: Add request_partial_firmware_into_buf() Kees Cook
2020-07-29  1:17   ` Luis Chamberlain
2020-07-29  6:22     ` Takashi Iwai
2020-07-29 17:43       ` Kees Cook
2020-07-24 21:36 ` [PATCH v3 19/19] test_firmware: Test partial read support Kees Cook
2020-07-25  5:14 ` [PATCH v3 00/19] Introduce partial kernel_read_file() support Scott Branden
2020-07-25 10:05 ` Greg Kroah-Hartman
2020-07-25 15:48   ` Kees Cook
2020-07-27 11:16 ` Mimi Zohar
2020-07-27 19:18   ` Scott Branden
2020-07-28 18:48     ` Mimi Zohar
2020-07-28 19:56       ` Scott Branden
2020-07-29  1:19 ` Luis Chamberlain

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