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[73.71.40.85]) by smtp.gmail.com with ESMTPSA id 137sm436785ywv.108.2019.02.04.14.30.27 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Mon, 04 Feb 2019 14:30:29 -0800 (PST) Received: by garbanzo.do-not-panic.com (sSMTP sendmail emulation); Mon, 04 Feb 2019 14:30:26 -0800 Date: Mon, 4 Feb 2019 14:30:26 -0800 From: Luis Chamberlain To: Mimi Zohar Cc: linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Jessica Yu , David Howells , Seth Forshee , Justin Forbes , Matthew Garrett Subject: Re: [PATCH] x86/ima: require signed kernel modules Message-ID: <20190204223026.GR11489@garbanzo.do-not-panic.com> References: <1548962339-10681-1-git-send-email-zohar@linux.ibm.com> <1548962339-10681-2-git-send-email-zohar@linux.ibm.com> <20190204203850.GP11489@garbanzo.do-not-panic.com> <1549317910.4146.124.camel@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1549317910.4146.124.camel@linux.ibm.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 04, 2019 at 05:05:10PM -0500, Mimi Zohar wrote: > On Mon, 2019-02-04 at 12:38 -0800, Luis Chamberlain wrote: > > On Thu, Jan 31, 2019 at 02:18:59PM -0500, Mimi Zohar wrote: > > > diff --git a/kernel/module.c b/kernel/module.c > > > index 2ad1b5239910..70a9709d19eb 100644 > > > --- a/kernel/module.c > > > +++ b/kernel/module.c > > > @@ -275,16 +275,23 @@ static void module_assert_mutex_or_preempt(void) > > > > > > static bool sig_enforce = IS_ENABLED(CONFIG_MODULE_SIG_FORCE); > > > module_param(sig_enforce, bool_enable_only, 0644); > > > +static bool sig_required; > > > > > > /* > > > * Export sig_enforce kernel cmdline parameter to allow other subsystems rely > > > * on that instead of directly to CONFIG_MODULE_SIG_FORCE config. > > > > But the docs were't updated. > > Neither "CONFIG_MODULE_SIG_FORCE" nor "module.sig_enforce" has > changed.  Which docs are you referring to?  You renamed is_module_sig_enforced() to is_module_sig_enforced_or_required() and left the above doc which only justifies the enforced path. > > > */ > > > -bool is_module_sig_enforced(void) > > > +bool is_module_sig_enforced_or_required(void) > > > { > > > - return sig_enforce; > > > + return sig_enforce || sig_required; > > > } > > > -EXPORT_SYMBOL(is_module_sig_enforced); > > > +EXPORT_SYMBOL(is_module_sig_enforced_or_required); > > > > Meh, this is getting sloppy, the module signing infrastructure should > > just be LSM'ified now that we have stacked LSMs. That would > > compartamentaliz that code and make this much easier to read / understand > > and mantain. > > > > Can you take a look at doing it that way instead? > > This patch is about coordinating the existing methods of verifying > kernel module signatures. I understand. > > > > > /* Block module loading/unloading? */ > > > int modules_disabled = 0; > > > @@ -2789,7 +2796,7 @@ static int module_sig_check(struct load_info *info, int flags) > > > } > > > > > > /* Not having a signature is only an error if we're strict. */ > > > - if (err == -ENOKEY && !is_module_sig_enforced()) > > > + if (err == -ENOKEY && !is_module_sig_enforced_or_required()) > > > > This is where I think a proper LSM hook would make sense. I think > > that these "questions" model for signing don't work well on the LSM > > hook model, perhaps just: > > > > kernel_module_signed() > > > > Suffices, therefore if not enforced or required its signed. If its > > enforced or required and really signed, then it signed. > > > > > err = 0; > > > > > > return err; > > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c > > > index 357edd140c09..bbaf87f688be 100644 > > > --- a/security/integrity/ima/ima_main.c > > > +++ b/security/integrity/ima/ima_main.c > > > @@ -563,7 +563,7 @@ int ima_load_data(enum kernel_load_data_id id) > > > } > > > break; > > > case LOADING_MODULE: > > > - sig_enforce = is_module_sig_enforced(); > > > + sig_enforce = is_module_sig_enforced_or_required(); > > > > Yet another user. > > > > > if (ima_enforce && (!sig_enforce > > > && (ima_appraise & IMA_APPRAISE_MODULES))) { > > > -- > > > 2.7.5 > > > > Plus I think LSM'ifying module signing may help cleaning up some of the > > #ifdery and config options around module signing. I'm suggestin this now > > as this has been on my mental TODO list for a while, and just not sure > > when we'd get to it, if not you, not sure when it'd get done. > > > > Then, do we have proper unit tests for the mixture of options to ensure > > we can easily ensure we don't regress? > > > > There are already two methods  - appended signatures and IMA xattrs - > for validating kernel modules. > > Kernel modules shouldn't be treated any differently than any other > file. The good 'ol kernel module signing code *does* treat it as such. > Based on the IMA policy, the kernel module signature can be > verified.  Also based on the IMA policy, the file hash added to the > measurement list, and the file hash used to extend the TPM PCR. >  Lastly, based on policy the file hash can be added to the audit log. Sure... > I don't see a need for an additional LSM just for verifying kernel > module signatures. But it is one, module signing was just spawned pre the boom of LSMs. I do believe that treating the code as such would help with its reading and long term maintenance. Anyway, I had to try to convince you. Luis