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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 2 Oct 2018 09:54:05 -0700
Message-ID: <CAGXu5jKqXNbEvPr1axQtGCCnWsGhDgjynW5u326mcx4vZ1oH8g@mail.gmail.com>
Subject: Re: [PATCH security-next v4 23/32] selinux: Remove boot parameter
To:     Jordan Glover <Golden_Miller83@protonmail.ch>
Cc:     Stephen Smalley <sds@tycho.nsa.gov>,
        Paul Moore <paul@paul-moore.com>,
        James Morris <jmorris@namei.org>,
        Casey Schaufler <casey@schaufler-ca.com>,
        John Johansen <john.johansen@canonical.com>,
        Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        "Schaufler, Casey" <casey.schaufler@intel.com>,
        linux-security-module <linux-security-module@vger.kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Oct 2, 2018 at 9:33 AM, Jordan Glover
<Golden_Miller83@protonmail.ch> wrote:
> It's always documented as: "selinux=1 security=selinux" so security= should
> still do the job and selinux=1 become no-op, no?

The v3 patch set worked this way, yes. (The per-LSM enable defaults
were set by the LSM. Only in the case of "lsm.disable=selinux" would
the above stop working.)

John did not like the separation of having two CONFIG and two
bootparams mixing the controls. The v3 resolution rules were:

SECURITY_SELINUX_BOOTPARAM_VALUE overrides CONFIG_LSM_ENABLE.
SECURITY_APPARMOR_BOOTPARAM_VALUE overrides CONFIG_LSM_ENABLE.
selinux= overrides SECURITY_SELINUX_BOOTPARAM_VALUE.
apparmor.enabled= overrides SECURITY_APPARMOR_BOOTPARAM_VALUE.
apparmor= overrides apparmor.enabled=.
lsm.enable= overrides selinux=.
lsm.enable= overrides apparmor=.
lsm.disable= overrides lsm.enable=.
major LSM _omission_ from security= (if present) overrides lsm.enable.

v4 removed the per-LSM boot params and CONFIGs at John's request, but
Paul and Stephen don't want this for SELinux.

The pieces for reducing conflict with CONFIG_LSM_ENABLE and
lsm.{enable,disable}= were:

1- Remove SECURITY_APPARMOR_BOOTPARAM_VALUE.
2- Remove apparmor= and apparmor.enabled=.
3- Remove SECURITY_SELINUX_BOOTPARAM_VALUE.
4- Remove selinux=.

v4 used all of 1-4 above. SELinux says "4" cannot happen as it's too
commonly used. Would 3 be okay for SELinux?

John, with 4 not happening, do you prefer to not have 2 happen?

With CONFIGs removed, then the boot time defaults are controlled by
CONFIG_LSM_ENABLE, but the boot params continue to work as before.
Only the use of the new lsm.enable= and lsm.disable= would override
the per-LSM boot params. This would clean up the build-time CONFIG
weirdness, and leave the existing boot params as before (putting us
functionally in between the v3 and v4 series).

-Kees

-- 
Kees Cook
Pixel Security