From: ebiederm@xmission.com (Eric W. Biederman)
To: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>,
Matthew Garrett <mjg59@google.com>,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] kexec: call LSM hook for kexec_load syscall
Date: Thu, 03 May 2018 10:51:38 -0500 [thread overview]
Message-ID: <87h8nospo5.fsf@xmission.com> (raw)
In-Reply-To: <1525275904.5669.308.camel@linux.vnet.ibm.com> (Mimi Zohar's message of "Wed, 02 May 2018 11:45:04 -0400")
Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote:
>> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
>>
>> > Allow LSMs and IMA to differentiate between the kexec_load and
>> > kexec_file_load syscalls by adding an "unnecessary" call to
>> > security_kernel_read_file() in kexec_load. This would be similar to the
>> > existing init_module syscall calling security_kernel_read_file().
>>
>> Given the reasonable desire to load a policy that ensures everything
>> has a signature I don't have fundamental objections.
>>
>> security_kernel_read_file as a hook seems an odd choice. At the very
>> least it has a bad name because there is no file reading going on here.
>>
>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested
>> anywhere. Which means I could have a kernel compiled without that and I
>> would be allowed to use kexec_file_load without signature checking.
>> While kexec_load would be denied.
>>
>> Am I missing something here?
>
> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn
> calls security_kernel_read_file(). So kexec_file_load and kexec_load
> syscall would be using the same method for enforcing signature
> verification.
Having looked at your patches and the kernel a little more I think
this should be a separate security hook that does not take a file
parameter.
Right now every other security module assumes !file is init_module.
So I think this change has the potential to confuse other security
modules, with the result of unintended policy being applied.
So just for good security module hygeine I think this needs a dedicated
kexec_load security hook.
> This is independent of the architecture specific method for verifying
> signatures. The coordination between these two methods was included
> in the lockdown patch set, but is being removed, as well the gating of
> kexec_load syscall. Instead of being based on the lockdown flag, I
> assume the coordination between the two methods will reappear based on
> a secure boot flag of some sort.
I was blind there for a moment. Yes this is all about the ima xattrs
allowing a file to be loaded.
Eric
WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman)
To: linux-security-module@vger.kernel.org
Subject: [PATCH 2/3] kexec: call LSM hook for kexec_load syscall
Date: Thu, 03 May 2018 10:51:38 -0500 [thread overview]
Message-ID: <87h8nospo5.fsf@xmission.com> (raw)
In-Reply-To: <1525275904.5669.308.camel@linux.vnet.ibm.com> (Mimi Zohar's message of "Wed, 02 May 2018 11:45:04 -0400")
Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote:
>> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
>>
>> > Allow LSMs and IMA to differentiate between the kexec_load and
>> > kexec_file_load syscalls by adding an "unnecessary" call to
>> > security_kernel_read_file() in kexec_load. This would be similar to the
>> > existing init_module syscall calling security_kernel_read_file().
>>
>> Given the reasonable desire to load a policy that ensures everything
>> has a signature I don't have fundamental objections.
>>
>> security_kernel_read_file as a hook seems an odd choice. At the very
>> least it has a bad name because there is no file reading going on here.
>>
>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested
>> anywhere. Which means I could have a kernel compiled without that and I
>> would be allowed to use kexec_file_load without signature checking.
>> While kexec_load would be denied.
>>
>> Am I missing something here?
>
> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn
> calls security_kernel_read_file(). ?So kexec_file_load and kexec_load
> syscall would be using the same method for enforcing signature
> verification.
Having looked at your patches and the kernel a little more I think
this should be a separate security hook that does not take a file
parameter.
Right now every other security module assumes !file is init_module.
So I think this change has the potential to confuse other security
modules, with the result of unintended policy being applied.
So just for good security module hygeine I think this needs a dedicated
kexec_load security hook.
> This is independent of the architecture specific method for verifying
> signatures. ?The coordination between these two methods was included
> in the lockdown patch set, but is being removed, as well the gating of
> kexec_load syscall. ?Instead of being based on the lockdown flag, I
> assume the coordination between the two methods will reappear based on
> a secure boot flag of some sort.
I was blind there for a moment. Yes this is all about the ima xattrs
allowing a file to be loaded.
Eric
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WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman)
To: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: David Howells <dhowells@redhat.com>,
Matthew Garrett <mjg59@google.com>,
linux-integrity@vger.kernel.org,
linux-security-module@vger.kernel.org, kexec@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] kexec: call LSM hook for kexec_load syscall
Date: Thu, 03 May 2018 10:51:38 -0500 [thread overview]
Message-ID: <87h8nospo5.fsf@xmission.com> (raw)
In-Reply-To: <1525275904.5669.308.camel@linux.vnet.ibm.com> (Mimi Zohar's message of "Wed, 02 May 2018 11:45:04 -0400")
Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote:
>> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
>>
>> > Allow LSMs and IMA to differentiate between the kexec_load and
>> > kexec_file_load syscalls by adding an "unnecessary" call to
>> > security_kernel_read_file() in kexec_load. This would be similar to the
>> > existing init_module syscall calling security_kernel_read_file().
>>
>> Given the reasonable desire to load a policy that ensures everything
>> has a signature I don't have fundamental objections.
>>
>> security_kernel_read_file as a hook seems an odd choice. At the very
>> least it has a bad name because there is no file reading going on here.
>>
>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested
>> anywhere. Which means I could have a kernel compiled without that and I
>> would be allowed to use kexec_file_load without signature checking.
>> While kexec_load would be denied.
>>
>> Am I missing something here?
>
> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn
> calls security_kernel_read_file(). So kexec_file_load and kexec_load
> syscall would be using the same method for enforcing signature
> verification.
Having looked at your patches and the kernel a little more I think
this should be a separate security hook that does not take a file
parameter.
Right now every other security module assumes !file is init_module.
So I think this change has the potential to confuse other security
modules, with the result of unintended policy being applied.
So just for good security module hygeine I think this needs a dedicated
kexec_load security hook.
> This is independent of the architecture specific method for verifying
> signatures. The coordination between these two methods was included
> in the lockdown patch set, but is being removed, as well the gating of
> kexec_load syscall. Instead of being based on the lockdown flag, I
> assume the coordination between the two methods will reappear based on
> a secure boot flag of some sort.
I was blind there for a moment. Yes this is all about the ima xattrs
allowing a file to be loaded.
Eric
WARNING: multiple messages have this Message-ID (diff)
From: ebiederm@xmission.com (Eric W. Biederman)
To: Mimi Zohar <zohar@linux.vnet.ibm.com>
Cc: kexec@lists.infradead.org, linux-kernel@vger.kernel.org,
Matthew Garrett <mjg59@google.com>,
David Howells <dhowells@redhat.com>,
linux-security-module@vger.kernel.org,
linux-integrity@vger.kernel.org
Subject: Re: [PATCH 2/3] kexec: call LSM hook for kexec_load syscall
Date: Thu, 03 May 2018 10:51:38 -0500 [thread overview]
Message-ID: <87h8nospo5.fsf@xmission.com> (raw)
In-Reply-To: <1525275904.5669.308.camel@linux.vnet.ibm.com> (Mimi Zohar's message of "Wed, 02 May 2018 11:45:04 -0400")
Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
> On Wed, 2018-05-02 at 09:45 -0500, Eric W. Biederman wrote:
>> Mimi Zohar <zohar@linux.vnet.ibm.com> writes:
>>
>> > Allow LSMs and IMA to differentiate between the kexec_load and
>> > kexec_file_load syscalls by adding an "unnecessary" call to
>> > security_kernel_read_file() in kexec_load. This would be similar to the
>> > existing init_module syscall calling security_kernel_read_file().
>>
>> Given the reasonable desire to load a policy that ensures everything
>> has a signature I don't have fundamental objections.
>>
>> security_kernel_read_file as a hook seems an odd choice. At the very
>> least it has a bad name because there is no file reading going on here.
>>
>> I am concerned that I don't see CONFIG_KEXEC_VERIFY_SIG being tested
>> anywhere. Which means I could have a kernel compiled without that and I
>> would be allowed to use kexec_file_load without signature checking.
>> While kexec_load would be denied.
>>
>> Am I missing something here?
>
> The kexec_file_load() calls kernel_read_file_from_fd(), which in turn
> calls security_kernel_read_file(). So kexec_file_load and kexec_load
> syscall would be using the same method for enforcing signature
> verification.
Having looked at your patches and the kernel a little more I think
this should be a separate security hook that does not take a file
parameter.
Right now every other security module assumes !file is init_module.
So I think this change has the potential to confuse other security
modules, with the result of unintended policy being applied.
So just for good security module hygeine I think this needs a dedicated
kexec_load security hook.
> This is independent of the architecture specific method for verifying
> signatures. The coordination between these two methods was included
> in the lockdown patch set, but is being removed, as well the gating of
> kexec_load syscall. Instead of being based on the lockdown flag, I
> assume the coordination between the two methods will reappear based on
> a secure boot flag of some sort.
I was blind there for a moment. Yes this is all about the ima xattrs
allowing a file to be loaded.
Eric
_______________________________________________
kexec mailing list
kexec@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/kexec
next prev parent reply other threads:[~2018-05-03 15:51 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 22:41 [PATCH 0/3] kexec: limit kexec_load syscall Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-04-12 22:41 ` [PATCH 1/3] ima: based on the "secure_boot" policy limit syscalls Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-04-12 22:41 ` [PATCH 2/3] kexec: call LSM hook for kexec_load syscall Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-05-02 13:33 ` Mimi Zohar
2018-05-02 13:33 ` Mimi Zohar
2018-05-02 14:45 ` Eric W. Biederman
2018-05-02 14:45 ` Eric W. Biederman
2018-05-02 14:45 ` Eric W. Biederman
2018-05-02 15:45 ` Mimi Zohar
2018-05-02 15:45 ` Mimi Zohar
2018-05-02 15:45 ` Mimi Zohar
2018-05-02 15:45 ` Mimi Zohar
2018-05-03 15:51 ` Eric W. Biederman [this message]
2018-05-03 15:51 ` Eric W. Biederman
2018-05-03 15:51 ` Eric W. Biederman
2018-05-03 15:51 ` Eric W. Biederman
2018-05-03 16:05 ` Casey Schaufler
2018-05-03 16:05 ` Casey Schaufler
2018-05-03 16:05 ` Casey Schaufler
2018-05-03 16:05 ` Casey Schaufler
2018-05-03 16:42 ` Eric W. Biederman
2018-05-03 16:42 ` Eric W. Biederman
2018-05-03 16:42 ` Eric W. Biederman
2018-05-03 16:42 ` Eric W. Biederman
2018-05-03 21:06 ` Mimi Zohar
2018-05-03 21:06 ` Mimi Zohar
2018-05-03 21:06 ` Mimi Zohar
2018-05-03 21:06 ` Mimi Zohar
2018-05-03 21:36 ` Eric W. Biederman
2018-05-03 21:36 ` Eric W. Biederman
2018-05-03 21:36 ` Eric W. Biederman
2018-05-03 21:36 ` Eric W. Biederman
2018-04-12 22:41 ` [PATCH 3/3] ima: based on policy require signed kexec kernel images Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-04-12 22:41 ` Mimi Zohar
2018-05-03 20:13 ` [PATCH 0/3] kexec: limit kexec_load syscall Eric W. Biederman
2018-05-03 20:13 ` Eric W. Biederman
2018-05-03 20:13 ` Eric W. Biederman
2018-05-03 20:39 ` Matthew Garrett
2018-05-03 20:39 ` Matthew Garrett
2018-05-03 20:39 ` Matthew Garrett
2018-05-03 21:58 ` Eric W. Biederman
2018-05-03 21:58 ` Eric W. Biederman
2018-05-03 21:58 ` Eric W. Biederman
2018-05-03 22:51 ` Matthew Garrett
2018-05-03 22:51 ` Matthew Garrett
2018-05-03 22:51 ` Matthew Garrett
2018-05-03 21:31 ` Mimi Zohar
2018-05-03 21:31 ` Mimi Zohar
2018-05-03 21:31 ` Mimi Zohar
2018-05-03 21:31 ` Mimi Zohar
2018-05-03 21:38 ` Eric W. Biederman
2018-05-03 21:38 ` Eric W. Biederman
2018-05-03 21:38 ` Eric W. Biederman
2018-05-03 21:38 ` Eric W. Biederman
2018-05-03 21:57 ` Mimi Zohar
2018-05-03 21:57 ` Mimi Zohar
2018-05-03 21:57 ` Mimi Zohar
2018-05-03 21:57 ` Mimi Zohar
2018-05-03 23:03 ` Eric W. Biederman
2018-05-03 23:03 ` Eric W. Biederman
2018-05-03 23:03 ` Eric W. Biederman
2018-05-03 23:03 ` Eric W. Biederman
2018-05-04 2:29 ` Mimi Zohar
2018-05-04 2:29 ` Mimi Zohar
2018-05-04 2:29 ` Mimi Zohar
2018-05-04 2:29 ` Mimi Zohar
2018-05-11 1:36 Mimi Zohar
2018-05-11 1:36 ` [PATCH 2/3] kexec: call LSM hook for " Mimi Zohar
2018-05-11 1:36 ` Mimi Zohar
2018-05-11 1:36 ` Mimi Zohar
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