linux-kernel - Re: Linux Firmware Signing

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Date:	Wed, 02 Sep 2015 20:05:36 -0400
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	Kees Cook <keescook@...omium.org>,
	David Woodhouse <dwmw2@...radead.org>,
	David Howells <dhowells@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	"Roberts, William C" <william.c.roberts@...el.com>,
	"linux-security-module@...r.kernel.org" 
	<linux-security-module@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	"james.l.morris@...cle.com" <james.l.morris@...cle.com>,
	"serge@...lyn.com" <serge@...lyn.com>,
	Vitaly Kuznetsov <vkuznets@...hat.com>,
	Paul Moore <paul@...l-moore.com>,
	Eric Paris <eparis@...isplace.org>,
	SE Linux <selinux@...ho.nsa.gov>,
	Stephen Smalley <sds@...ho.nsa.gov>,
	"Schaufler, Casey" <casey.schaufler@...el.com>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Peter Jones <pjones@...hat.com>, Takashi Iwai <tiwai@...e.de>,
	Ming Lei <ming.lei@...onical.com>, Joey Lee <jlee@...e.de>,
	Vojtěch Pavlík <vojtech@...e.com>,
	Kyle McMartin <kyle@...nel.org>,
	Seth Forshee <seth.forshee@...onical.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Johannes Berg <johannes@...solutions.net>,
	Jay Schulist <jschlst@...ba.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Alexei Starovoitov <ast@...mgrid.com>
Subject: Re: Linux Firmware Signing

On Wed, 2015-09-02 at 20:46 +0200, Luis R. Rodriguez wrote:
> On Tue, Sep 01, 2015 at 11:35:05PM -0400, Mimi Zohar wrote:
> > > OK great, I think that instead of passing the actual routine name we should
> > > instead pass an enum type for to the LSM, that'd be easier to parse and we'd
> > > then have each case well documented. Each LSM then could add its own
> > > documetnation for this and can switch on it. If we went with a name we'd have
> > > to to use something like __func__ and then parse that, its not clear if we need
> > > to get that specific.
> > 
> > Agreed.  IMA already defines an enumeration.
> > 
> > /* IMA policy related functions */
> > enum ima_hooks { FILE_CHECK = 1, MMAP_CHECK, BPRM_CHECK, MODULE_CHECK,
> >                  FIRMWARE_CHECK, POLICY_CHECK, POST_SETATTR };
> > 
> 
> We want something that is not only useful for IMA but any other LSM,
> and FILE_CHECK seems very broad, not sure what BPRM_CHECK is even upon
> inspecting kernel code. Likewise for POST_SETATTR. POLICY_CHECK might
> be broad, perhaps its best we define then a generic set of enums to
> which IMA can map them to then and let it decide. This would ensure
> that the kernel defines each use caes for file inspection carefully,
> documents and defines them and if an LSM wants to bunch a set together
> it can do so easily with a switch statement to map set of generic
> file checks in kernel to a group it already handles.

The names are based on the calling security hook.   For a description of
each of these security hooks refer to include/linux/lsm_hooks.h.
 
> For instance at least in the short term we'd try to unify:
> 
> security_kernel_fw_from_file()
> security_kernel_module_from_file()
> 
> to perhaps:
> 
> security_kernel_from_file()
> 
> As far, as far as I can tell, the only ones we'd be ready to start
> grouping immediately or with small amount of work rather soon:
> 
> /**
>  *
>  * enum security_filecheck - known kernel security file checks types
>  *
>  * @__SECURITY_FILECHECK_UNSPEC: attribute 0 reserved
>  * @SECURITY_FILECHECK_MODULE: the file being processed is a Linux kernel module
>  * @SECURITY_FILECHECK_SYSDATA: the file being processed is either a firmware
>  *	file or a system data file read from /lib/firmware/* by firmware_class
>  * @SECURITY_FILECHECK_KEXEC_KERNEL: the file being processed is a kernel file
>  * 	used by kexec
>  * @SECURITY_FILECHECK_KEXEC_INITRAMFS: the file being processed is an initramfs
>  * 	used by kexec
> 
>  * The kernel reads files directly from the filesystem for a series of
>  * operations.  The list of files the kernel reads from the filesystem are
>  * limited and each type of file consumed may have a different format and
>  * security vetting procedures. The kernel enables LSMs to vet for these files
>  * through a shared LSM hook prior to consumption. This list documents the
>  * different special kernel file types read by the kernel, it enables LSMs
>  * to vet for each differently if needed.
> enum security_filecheck {
> 	SECURITY_FILECHECK_UNSPEC,
> 	SECURITY_FILECHECK_MODULE,
> 	SECURITY_FILECHECK_SYSDATA,
> 	SECURITY_FILECHECK_KEXEC_KERNEL,
> 	SECURITY_FILECHECK_KEXEC_INITRAMFS,
> };
> 
> Provided the MOK thing or alternative gets addressed we could also soon add
> something for SELinux policy files but that needs to be discussed further
> it seems. If MOK is used would SECURITY_FILECHECK_POLICY_MOK be OK? Again
> this would likely need further discussion, its why I didn't list it above.

Oh, I'm really confused as to why MOK would be a separate hook.  I
thought the discussion was about using a key in the UEFI MOK DB for
verifying locally signed files.

Mimi  

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