On 10/3/18 4:55 PM, Kees Cook wrote: > On Wed, Oct 3, 2018 at 2:34 PM, James Morris <jmorris@xxxxxxxxx> wrote: >> On Wed, 3 Oct 2018, Kees Cook wrote: >> >>> On Wed, Oct 3, 2018 at 11:28 AM, James Morris <jmorris@xxxxxxxxx> wrote: >>>> On Wed, 3 Oct 2018, Kees Cook wrote: >>>> >>>>> On Wed, Oct 3, 2018 at 11:17 AM, James Morris <jmorris@xxxxxxxxx> wrote: >>>>>> On Tue, 2 Oct 2018, John Johansen wrote: >>>>>>> To me a list like >>>>>>> lsm.enable=X,Y,Z >>>>>> >>>>>> What about even simpler: >>>>>> >>>>>> lsm=selinux,!apparmor,yama >>>>> >>>>> We're going to have lsm.order=, so I'd like to keep it with a dot >>>>> separator (this makes it more like module parameters, too). You want >>>>> to mix enable/disable in the same string? That implies you'd want >>>>> implicit enabling (i.e. it complements the builtin enabling), which is >>>>> opposite from what John wanted. >>>>> >>>> >>>> Why can't this be the order as well? >>> >>> That was covered extensively in the earlier threads. It boils down to >>> making sure we do not create a pattern of leaving LSMs disabled by >>> default when they are added to the kernel. The v1 series used >>> security= like this: >>> >>> + security= [SECURITY] An ordered comma-separated list of >>> + security modules to attempt to enable at boot. If >>> + this boot parameter is not specified, only the >>> + security modules asking for initialization will be >>> + enabled (see CONFIG_DEFAULT_SECURITY). Duplicate >>> + or invalid security modules will be ignored. The >>> + capability module is always loaded first, without >>> + regard to this parameter. >>> >>> This meant booting "security=apparmor" would disable all the other >>> LSMs, which wasn't friendly at all. So "security=" was left alone (to >>> leave it to only select the "major" LSM: all major LSMs not matching >>> "security=" would be disabled). So I proposed "lsm.order=" to specify >>> the order things were going to be initialized in, but to avoid kernels >>> booting with newly added LSMs forced-off due to not being listed in >>> "lsm.order=", it had to have implicit fall-back for unlisted LSMs. >>> (i.e. anything missing from lsm.order would then follow their order in >>> CONFIG_LSM_ORDER, and anything missing there would fall back to >>> link-time ordering.) However, then the objection was raised that this >>> didn't provide a way to explicitly disable an LSM. So I proposed >>> lsm.enable/disable, and John argued for CONFIG_LSM_ENABLE over >>> CONFIG_LSM_DISABLE. >> >> Ok, but it may end up being clearer, simpler, and thus more secure to just >> have a single way to configure LSM. >> >> For example: >> >> - All LSMs which are built are NOT enabled by default >> >> - You specify enablement and order via a Kconfig: >> >> CONFIG_LSM="selinux,yama" >> >> - This can be entirely overridden by a boot param: >> >> lsm="apparmor,landlock" > > This doesn't work with how SELinux and AppArmor do their bootparams, > unfortunately. (And Paul and Stephen have expressed that the > documented selinux on/off must continue to work.) For example, let's > say you've built an Ubuntu kernel with: > > CONFIG_SELINUX=y > ... > CONFIG_LSM="yama,apparmor" > > (i.e. you want SELinux available, but not enabled, so it's left out of > CONFIG_LSM) > > Then someone boots the system with: > > selinux=1 security=selinux > > In what order does selinux get initialized relative to yama? > (apparmor, flagged as a "legacy major", would have been disabled by > the "security=" not matching it.) > To me, "security=selinux" means SELinux and nothing else, so I think that all of these params are inviting a lot of confusion. Sorry, I don't have a good answer for this. > > The LSM order needs to be defined externally to enablement because > something may become enabled when not listed in the order. > > Now, maybe I misunderstood your earlier suggestion, and what you meant > was to do something like: > > CONFIG_LSM="yama,apparmor,!selinux" > > to mean "put selinux here in the order, but don't enable it". Then the > problem becomes what happens to an LSM that has been built in but not > listed in CONFIG_LSM? > > Related to that, this means that when new LSMs are added, they will > need to be added to any custom CONFIG_LSM= or lsm= parameters. If > that's really how we have to go, I'll accept it, but I think it's a > bit unfriendly. :P > > Another reason I don't like it is because it requires users to know > about all the LSMs to make changes. One LSM can't be added/removed > without specifying ALL of the LSMs. (i.e. there is no trivial way to > enable/disable a single LSM without it growing its own enable/disable > code as in SELinux/AppArmor. I'd hoped to make that easier for both > users and developers.) Again, I can live with it, but I think it's > unfriendly. > > I just want to have a direct I can go that meets all the requirements. > :) I'm fine to ignore my sense of aesthetics if everyone can agree on > the code. -- ~Randy
