Message-ID: <20150903002914.GM8051@wotan.suse.de>
Date:	Thu, 3 Sep 2015 02:29:14 +0200
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	Mimi Zohar <zohar@...ux.vnet.ibm.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, Sep 02, 2015 at 08:05:36PM -0400, Mimi Zohar wrote:
> 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.

I see, thanks, ok so BPRM_CHECK = for binary loading, are you folks
really wanting to unify LSM hooks for firmware, modules, and binary
data ?

POST_SETATTR seems to be for inode_post_setxattr, so that as well?

POLICY_CHECK seems broad, not sure what to relate that to exactly.
Is this just SELinux polify files? Or is this something more broad?

> > 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.

That's correct, and no I was not thinking of a separate hook but rather
a type that lets the LSM know that MOK was used to sign the file consumed.

  Luis
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