From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751965AbbFRCC3 (ORCPT ); Wed, 17 Jun 2015 22:02:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44506 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750800AbbFRCCW (ORCPT ); Wed, 17 Jun 2015 22:02:22 -0400 Date: Thu, 18 Jun 2015 10:02:09 +0800 From: Dave Young To: Vivek Goyal Cc: "Eric W. Biederman" , Josh Boyer , "Theodore Ts'o" , Petr Tesarik , kexec , "Linux-Kernel@Vger. Kernel. Org" , David Howells Subject: Re: kexec_load(2) bypasses signature verification Message-ID: <20150618020209.GA8390@dhcp-128-32.nay.redhat.com> References: <20150615035051.GA2634@thunk.org> <20150615131728.GK15793@thunk.org> <20150615200115.GG5003@thunk.org> <87zj3zigug.fsf@x220.int.ebiederm.org> <20150616202757.GB14943@redhat.com> <87y4jjglvu.fsf@x220.int.ebiederm.org> <20150617014737.GB30214@redhat.com> <20150618011629.GA8718@dhcp-128-32.nay.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150618011629.GA8718@dhcp-128-32.nay.redhat.com> User-Agent: Mutt/1.5.22.1-rc1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/18/15 at 09:16am, Dave Young wrote: > On 06/16/15 at 09:47pm, Vivek Goyal wrote: > > On Tue, Jun 16, 2015 at 08:32:37PM -0500, Eric W. Biederman wrote: > > > Vivek Goyal writes: > > > > > > > On Tue, Jun 16, 2015 at 02:38:31PM -0500, Eric W. Biederman wrote: > > > >> > > > >> Adding Vivek as he is the one who implemented kexec_file_load. > > > >> I was hoping he would respond to this thread, and it looks like he > > > >> simply has not ever been Cc'd. > > > >> > > > >> Theodore Ts'o writes: > > > >> > > > >> > On Mon, Jun 15, 2015 at 09:37:05AM -0400, Josh Boyer wrote: > > > >> >> The bits that actually read Secure Boot state out of the UEFI > > > >> >> variables, and apply protections to the machine to avoid compromise > > > >> >> under the SB threat model. Things like disabling the old kexec... > > > >> > > > > >> > I don't have any real interest in using Secure Boot, but I *am* > > > >> > interested in using CONFIG_KEXEC_VERIFY_SIG[1]. So perhaps we need to > > > >> > have something similar to what we have with signed modules in terms of > > > >> > CONFIG_MODULE_SIG_FORCE and module/sig_enforce, but for > > > >> > KEXEC_VERIFY_SIG. This would mean creating a separate flag > > > >> > independent of the one Linus suggested for Secure Boot, but since we > > > >> > have one for signed modules, we do have precedent for this sort of > > > >> > thing. > > > >> > > > >> My overall request with respect to kexec has been that we implement > > > >> things that make sense outside of the bizarre threat model of the Linux > > > >> folks who were talking about secure boot. > > > >> > > > >> nI have not navigated the labyrinth of config options but having a way to > > > >> only boot signed things with kexec seems a completely sensible way to > > > >> operate in the context of signed images. > > > >> > > > >> I don't know how much that will help given that actors with sufficient > > > >> resources have demonstrated the ability to steal private keys, but > > > >> assuming binary signing is an effective technique (or why else do it) > > > >> then having an option to limit kexec to only loading signed images seems > > > >> sensible. > > > > > > > > I went through the mail chain on web and here are my thoughts. > > > > > > > > - So yes, upstream does not have the logic which automatically disables > > > > the old syscall (kexec_load()) on secureboot systems. Distributions > > > > carry those patches. > > > > > > > > - This KEXEC_VERIFY_SIG option only cotrols the behavior for > > > > kexec_file_load() syscall and is not meant to directly affect any > > > > behavior of old syscall (kexec_load()). I think I should have named > > > > it KEXEC_FILE_VERIFY_SIG. Though help text makes it clear. > > > > "Verify kernel signature during kexec_file_load() syscall". > > > > > > > > - I think disabling old system call if KEXEC_VERIFY_SIG() is set > > > > will break existing setup which use old system call by default, except > > > > the case of secureboot system. And old syscall path is well tested > > > > and new syscall might not be in a position to support all the corner > > > > cases, atleast as of now. > > > > > > > > Ted, > > > > > > > > So looks like you are looking for a system/option where you just want to > > > > always make use of kexec_file_load() and disable kexec_load(). This sounds > > > > like you want a kernel where kexec_load() is compiled out and you want > > > > only kexec_file_load() in. > > > > > > > > Right now one can't do that becase kexec_file_load() depends on > > > > CONFIG_KEXEC option. > > > > > > > > I am wondering that how about making CONFIG_KEXEC_FILE_LOAD independent > > > > of CONFIG_KEXEC. That way one can set CONFIG_KEXEC_VERIFY_SIG=y, and > > > > only signed kernel can be kexeced on that system. > > > > > > > > This should gel well with long term strategy of deprecating kexec_load() > > > > at some point of time when kexec_file_load() is ready to completely > > > > replace it. > > > > > > Interesting. > > > > > > I suspect that what we want is to have CONFIG_KEXEC for the core > > > and additional CONFIG_KEXEC_LOAD option that covers that kexec_load call. > > > > > > That should make it trivially easy to disable the kexec_load system call > > > in cases where people care. > > > > Or, we could create another option CONFIG_KEXEC_CORE/CONFIG_KEXEC_COMMON > > which will be automatically selected when either CONFIG_KEXEC or > > CONIG_KEXEC_FILE are selected. > > > > All common code can go under this option and rest can go under respective > > config options. > > > > That way, those who have CONFIG_KEXEC=y in old config files will not be > > broken. They don't have to learn about new options at all. > > Or simply add a new config option KEXEC_VERIFY_SIG_FORCE, so we can return > error in kexec_load and print some error message. Just like below, does this work for you, Ted? --- arch/x86/Kconfig | 7 +++++++ kernel/kexec.c | 9 ++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) --- linux.orig/arch/x86/Kconfig +++ linux/arch/x86/Kconfig @@ -1755,6 +1755,13 @@ config KEXEC_VERIFY_SIG verification for the corresponding kernel image type being loaded in order for this to work. +config KEXEC_VERIFY_SIG_FORCE + bool "Enforce kexec signature verifying" + depends on KEXEC_VERIFY_SIG + ---help--- + This option disable kexec_load() syscall, only kexec_file_load + can be used. + config KEXEC_BZIMAGE_VERIFY_SIG bool "Enable bzImage signature verification support" depends on KEXEC_VERIFY_SIG --- linux.orig/kernel/kexec.c +++ linux/kernel/kexec.c @@ -45,6 +45,12 @@ #include #include +#ifdef CONFIG_KEXEC_VERIFY_SIG_FORCE +static bool kexec_verify_sig_force = true; +#else +static bool kexec_verify_sig_force; +#endif + /* Per cpu memory for storing cpu states in case of system crash. */ note_buf_t __percpu *crash_notes; @@ -1243,7 +1249,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned lon int result; /* We only trust the superuser with rebooting the system. */ - if (!capable(CAP_SYS_BOOT) || kexec_load_disabled) + if (!capable(CAP_SYS_BOOT) || kexec_load_disabled + || kexec_verify_sig_force) return -EPERM; /* From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx1.redhat.com ([209.132.183.28]) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Z5PAA-0005iK-Sg for kexec@lists.infradead.org; Thu, 18 Jun 2015 02:02:43 +0000 Date: Thu, 18 Jun 2015 10:02:09 +0800 From: Dave Young Subject: Re: kexec_load(2) bypasses signature verification Message-ID: <20150618020209.GA8390@dhcp-128-32.nay.redhat.com> References: <20150615035051.GA2634@thunk.org> <20150615131728.GK15793@thunk.org> <20150615200115.GG5003@thunk.org> <87zj3zigug.fsf@x220.int.ebiederm.org> <20150616202757.GB14943@redhat.com> <87y4jjglvu.fsf@x220.int.ebiederm.org> <20150617014737.GB30214@redhat.com> <20150618011629.GA8718@dhcp-128-32.nay.redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20150618011629.GA8718@dhcp-128-32.nay.redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Vivek Goyal Cc: Josh Boyer , Theodore Ts'o , kexec , Petr Tesarik , "Linux-Kernel@Vger. Kernel. Org" , David Howells , "Eric W. Biederman" On 06/18/15 at 09:16am, Dave Young wrote: > On 06/16/15 at 09:47pm, Vivek Goyal wrote: > > On Tue, Jun 16, 2015 at 08:32:37PM -0500, Eric W. Biederman wrote: > > > Vivek Goyal writes: > > > > > > > On Tue, Jun 16, 2015 at 02:38:31PM -0500, Eric W. Biederman wrote: > > > >> > > > >> Adding Vivek as he is the one who implemented kexec_file_load. > > > >> I was hoping he would respond to this thread, and it looks like he > > > >> simply has not ever been Cc'd. > > > >> > > > >> Theodore Ts'o writes: > > > >> > > > >> > On Mon, Jun 15, 2015 at 09:37:05AM -0400, Josh Boyer wrote: > > > >> >> The bits that actually read Secure Boot state out of the UEFI > > > >> >> variables, and apply protections to the machine to avoid compromise > > > >> >> under the SB threat model. Things like disabling the old kexec... > > > >> > > > > >> > I don't have any real interest in using Secure Boot, but I *am* > > > >> > interested in using CONFIG_KEXEC_VERIFY_SIG[1]. So perhaps we need to > > > >> > have something similar to what we have with signed modules in terms of > > > >> > CONFIG_MODULE_SIG_FORCE and module/sig_enforce, but for > > > >> > KEXEC_VERIFY_SIG. This would mean creating a separate flag > > > >> > independent of the one Linus suggested for Secure Boot, but since we > > > >> > have one for signed modules, we do have precedent for this sort of > > > >> > thing. > > > >> > > > >> My overall request with respect to kexec has been that we implement > > > >> things that make sense outside of the bizarre threat model of the Linux > > > >> folks who were talking about secure boot. > > > >> > > > >> nI have not navigated the labyrinth of config options but having a way to > > > >> only boot signed things with kexec seems a completely sensible way to > > > >> operate in the context of signed images. > > > >> > > > >> I don't know how much that will help given that actors with sufficient > > > >> resources have demonstrated the ability to steal private keys, but > > > >> assuming binary signing is an effective technique (or why else do it) > > > >> then having an option to limit kexec to only loading signed images seems > > > >> sensible. > > > > > > > > I went through the mail chain on web and here are my thoughts. > > > > > > > > - So yes, upstream does not have the logic which automatically disables > > > > the old syscall (kexec_load()) on secureboot systems. Distributions > > > > carry those patches. > > > > > > > > - This KEXEC_VERIFY_SIG option only cotrols the behavior for > > > > kexec_file_load() syscall and is not meant to directly affect any > > > > behavior of old syscall (kexec_load()). I think I should have named > > > > it KEXEC_FILE_VERIFY_SIG. Though help text makes it clear. > > > > "Verify kernel signature during kexec_file_load() syscall". > > > > > > > > - I think disabling old system call if KEXEC_VERIFY_SIG() is set > > > > will break existing setup which use old system call by default, except > > > > the case of secureboot system. And old syscall path is well tested > > > > and new syscall might not be in a position to support all the corner > > > > cases, atleast as of now. > > > > > > > > Ted, > > > > > > > > So looks like you are looking for a system/option where you just want to > > > > always make use of kexec_file_load() and disable kexec_load(). This sounds > > > > like you want a kernel where kexec_load() is compiled out and you want > > > > only kexec_file_load() in. > > > > > > > > Right now one can't do that becase kexec_file_load() depends on > > > > CONFIG_KEXEC option. > > > > > > > > I am wondering that how about making CONFIG_KEXEC_FILE_LOAD independent > > > > of CONFIG_KEXEC. That way one can set CONFIG_KEXEC_VERIFY_SIG=y, and > > > > only signed kernel can be kexeced on that system. > > > > > > > > This should gel well with long term strategy of deprecating kexec_load() > > > > at some point of time when kexec_file_load() is ready to completely > > > > replace it. > > > > > > Interesting. > > > > > > I suspect that what we want is to have CONFIG_KEXEC for the core > > > and additional CONFIG_KEXEC_LOAD option that covers that kexec_load call. > > > > > > That should make it trivially easy to disable the kexec_load system call > > > in cases where people care. > > > > Or, we could create another option CONFIG_KEXEC_CORE/CONFIG_KEXEC_COMMON > > which will be automatically selected when either CONFIG_KEXEC or > > CONIG_KEXEC_FILE are selected. > > > > All common code can go under this option and rest can go under respective > > config options. > > > > That way, those who have CONFIG_KEXEC=y in old config files will not be > > broken. They don't have to learn about new options at all. > > Or simply add a new config option KEXEC_VERIFY_SIG_FORCE, so we can return > error in kexec_load and print some error message. Just like below, does this work for you, Ted? --- arch/x86/Kconfig | 7 +++++++ kernel/kexec.c | 9 ++++++++- 2 files changed, 15 insertions(+), 1 deletion(-) --- linux.orig/arch/x86/Kconfig +++ linux/arch/x86/Kconfig @@ -1755,6 +1755,13 @@ config KEXEC_VERIFY_SIG verification for the corresponding kernel image type being loaded in order for this to work. +config KEXEC_VERIFY_SIG_FORCE + bool "Enforce kexec signature verifying" + depends on KEXEC_VERIFY_SIG + ---help--- + This option disable kexec_load() syscall, only kexec_file_load + can be used. + config KEXEC_BZIMAGE_VERIFY_SIG bool "Enable bzImage signature verification support" depends on KEXEC_VERIFY_SIG --- linux.orig/kernel/kexec.c +++ linux/kernel/kexec.c @@ -45,6 +45,12 @@ #include #include +#ifdef CONFIG_KEXEC_VERIFY_SIG_FORCE +static bool kexec_verify_sig_force = true; +#else +static bool kexec_verify_sig_force; +#endif + /* Per cpu memory for storing cpu states in case of system crash. */ note_buf_t __percpu *crash_notes; @@ -1243,7 +1249,8 @@ SYSCALL_DEFINE4(kexec_load, unsigned lon int result; /* We only trust the superuser with rebooting the system. */ - if (!capable(CAP_SYS_BOOT) || kexec_load_disabled) + if (!capable(CAP_SYS_BOOT) || kexec_load_disabled + || kexec_verify_sig_force) return -EPERM; /* _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec