From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Kees Cook <keescook@chromium.org>
Cc: Greg KH <gregkh@linuxfoundation.org>,
Matthew Garrett <matthew.garrett@nebula.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
"hpa@zytor.com" <hpa@zytor.com>
Subject: Re: [PATCH V3 08/11] kexec: Disable at runtime if the kernel enforces module loading restrictions
Date: Sun, 08 Sep 2013 10:11:24 -0700 [thread overview]
Message-ID: <1378660284.2429.11.camel@dabdike.int.hansenpartnership.com> (raw)
In-Reply-To: <CAGXu5jLwCt6RtQC+kxcUC69tMydx8DO2QWDv3jK6_mOyT_iNbA@mail.gmail.com>
On Sun, 2013-09-08 at 08:51 -0700, Kees Cook wrote:
> On Sun, Sep 8, 2013 at 12:24 AM, Greg KH <gregkh@linuxfoundation.org> wrote:
> > On Sun, Sep 08, 2013 at 06:44:08AM +0000, Matthew Garrett wrote:
> >> On Sat, 2013-09-07 at 23:40 -0700, Greg KH wrote:
> >> > If you apply this, you break everyone who is currently relying on kexec
> >> > (i.e. kdump, bootloaders, etc.), from using signed kernel modules, which
> >> > personally, seems like a very bad idea.
> >>
> >> Enforcing signed modules provides you with no additional security if you
> >> have kexec enabled. It's better to make that obvious.
> >
> > Then document the heck out of it, don't disable a valid use case just
> > because it possibly could be used in some way that is different from the
> > original system.
> >
> > If you take this to an extreme, kexec shouldn't be here at all, as it
> > can do anything in the kernel wherever it wants to.
> >
> > kexec has nothing to do with signed modules, don't tie them together.
>
> It's not accurate to say it has "nothing to do" with signed modules.
> The purpose of signed modules is to ensure the integrity of the
> running system against the root user.
That's not true if you look at the use cases. Distros use signed
modules to taint the kernel: insert an unsigned one and the kernel
taints; insert a properly signed one and it doesn't. They use it for
support to tell if you've been adhering to your contract. That use case
has nothing to do with security.
> It was, however, incomplete. Terrible analogy follows: signed modules
> was locking the front door, but we have all sorts of windows still
> open. This closes those windows. You're trying to say that shutting
> windows has nothing to do with lumber locks. While technically true,
> this is about the intent of the barriers.
>
> Anyone currently using signed modules (with sig_enforce) AND kexec is
> deluding themselves about what the state of their system's ring-0
> security stance is. Those people should be running without
> sig_enforce, and if they want both sig_enforce and kexec, then I would
> expect a follow-up patch from them to provide signed kexec support.
The analogy is rubbish. I can give away CAP_SYS_MODULE and enforce what
modules those I've given the permission to can insert by signing them.
I keep CAP_SYS_BOOT, so they can't use kexec to subvert this.
Your analogy seems to be giving away the whole root and then crying Dr
it hurts when I do this ...
James
next prev parent reply other threads:[~2013-09-08 17:11 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-03 23:50 Matthew Garrett
2013-09-03 23:50 ` [PATCH V3 01/11] Add secure_modules() call Matthew Garrett
2013-09-04 0:45 ` James Morris
2013-09-05 2:14 ` joeyli
2013-09-03 23:50 ` [PATCH V3 02/11] PCI: Lock down BAR access when module security is enabled Matthew Garrett
2013-09-04 0:45 ` James Morris
2013-09-04 16:57 ` David Woodhouse
2013-09-04 17:04 ` Matthew Garrett
2013-09-04 18:58 ` David Woodhouse
2013-09-04 19:01 ` Matthew Garrett
2013-09-04 19:31 ` David Woodhouse
2013-09-03 23:50 ` [PATCH V3 03/11] x86: Lock down IO port " Matthew Garrett
2013-09-04 0:45 ` James Morris
2013-09-05 3:52 ` H. Peter Anvin
2013-09-05 3:58 ` Matthew Garrett
2013-09-05 15:36 ` H. Peter Anvin
2013-09-03 23:50 ` [PATCH V3 04/11] ACPI: Limit access to custom_method Matthew Garrett
2013-09-04 0:46 ` James Morris
2013-09-03 23:50 ` [PATCH V3 05/11] asus-wmi: Restrict debugfs interface when module loading is restricted Matthew Garrett
2013-09-04 0:46 ` James Morris
2013-09-03 23:50 ` [PATCH V3 06/11] Restrict /dev/mem and /dev/kmem " Matthew Garrett
2013-09-04 0:47 ` James Morris
2013-09-03 23:50 ` [PATCH V3 07/11] acpi: Ignore acpi_rsdp kernel parameter " Matthew Garrett
2013-09-03 23:50 ` [PATCH V3 08/11] kexec: Disable at runtime if the kernel enforces module loading restrictions Matthew Garrett
2013-09-04 0:48 ` James Morris
2013-09-04 20:09 ` jerry.hoemann
2013-09-04 20:12 ` Matthew Garrett
2013-09-04 20:14 ` Josh Boyer
2013-09-08 6:40 ` Greg KH
2013-09-08 6:44 ` Matthew Garrett
2013-09-08 7:24 ` Greg KH
2013-09-08 14:40 ` Matthew Garrett
2013-09-08 15:51 ` Kees Cook
2013-09-08 16:18 ` Greg KH
2013-09-08 16:24 ` Matthew Garrett
2013-09-08 16:39 ` Greg KH
2013-09-08 16:59 ` Matthew Garrett
2013-09-08 17:22 ` Greg KH
2013-09-08 17:25 ` Matthew Garrett
2013-09-08 17:11 ` James Bottomley [this message]
2013-09-08 17:15 ` Matthew Garrett
2013-09-08 17:22 ` James Bottomley
2013-09-08 17:27 ` Matthew Garrett
2013-09-08 17:32 ` James Bottomley
2013-09-08 17:38 ` Matthew Garrett
2013-09-03 23:50 ` [PATCH V3 09/11] uswsusp: Disable when module loading is restricted Matthew Garrett
2013-09-04 0:48 ` James Morris
2013-09-05 3:20 ` joeyli
2013-09-03 23:50 ` [PATCH V3 10/11] x86: Restrict MSR access " Matthew Garrett
2013-09-04 0:49 ` James Morris
2013-09-03 23:50 ` [PATCH V3 11/11] Add option to automatically enforce module signatures when in Secure Boot mode Matthew Garrett
2013-09-04 1:42 ` James Morris
2013-09-04 1:42 ` Matthew Garrett
2013-09-05 3:13 ` joeyli
2013-09-05 8:24 ` joeyli
2013-09-05 10:16 ` Matt Fleming
2013-09-05 12:54 ` Matthew Garrett
2013-09-04 15:53 ` Kees Cook
2013-09-04 16:05 ` Re: Josh Boyer
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