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From: Andy Lutomirski <luto@amacapital.net>
To: James Morris <jmorris@namei.org>
Cc: Matthew Garrett <mjg59@google.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	David Howells <dhowells@redhat.com>,
	Linux API <linux-api@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH V32 01/27] Add the ability to lock down access to the running kernel image
Date: Thu, 2 May 2019 17:34:51 -0700	[thread overview]
Message-ID: <343EE650-4077-4882-94D6-28BBDBA32182@amacapital.net> (raw)
In-Reply-To: <alpine.LRH.2.21.1905030901180.7491@namei.org>


> On May 2, 2019, at 4:19 PM, James Morris <jmorris@namei.org> wrote:
> 
>> On Thu, 2 May 2019, Matthew Garrett wrote:
>> 
>>> On Thu, May 2, 2019 at 2:07 PM James Morris <jmorris@namei.org> wrote:
>>> One possible direction is to (as previously mentioned) assign IDs to each
>>> callsite and be able to check this ID against a simple policy array
>>> (allow/deny).  The default policy choices could be reduced to 'all' or
>>> 'none' during kconfig, and allow a custom policy to be loaded later if
>>> desired.
>> 
>> Ok. My primary concern around this is that it's very difficult to use
>> correctly in anything other than the "all" or "none" modes. If a new
>> kernel feature is added with integrated lockdown support, if an admin
>> is simply setting the flags of things they wish to block then this
>> will be left enabled - and may violate the admin's expectations around
>> integrity. On the other hand, if an admin is simply setting the flags
>> of things they wish to permit, then adding lockdown support to an
>> existing kernel feature may result in that feature suddenly being
>> disabled, which may also violate the admin's expectations around the
>> flags providing a stable set of behaviour.
> 
> Understood. Most uses will likely be either a distro or an embedded 
> system, who I'm assuming would provide a useful policy by default, and 
> perhaps a high-level abstraction for modification.
> 
>> Given that, would you prefer such a policy expression to look like?
> 
> Perhaps a write-once policy, injected from userspace during early boot?
> 
> The policy could be simply a list of:
> 
> lockdown_feature true|false
> 

I’m not convinced this is worthwhile.  As I see it, there really are only two privileges here: root can read kernel memory, and root can corrupt kernel state.  A policy that root can’t corrupt kernel memory except using, say, eBPF is useless — it gives warm fuzzy feelings but nothing else.

  reply	other threads:[~2019-05-03  0:34 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-04-04  0:32 [PATCH V32 0/27] Lockdown patches for 5.2 Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 01/27] Add the ability to lock down access to the running kernel image Matthew Garrett
2019-04-16  8:40   ` Andrew Donnellan
2019-04-16  8:40     ` Andrew Donnellan
2019-04-18  6:38     ` Daniel Axtens
2019-04-18  6:38       ` Daniel Axtens
2019-04-18 19:35     ` Matthew Garrett
2019-04-18 19:35       ` Matthew Garrett
2019-04-29  0:06       ` Daniel Axtens
2019-04-29  0:06         ` Daniel Axtens
2019-04-29  4:54         ` Daniel Axtens
2019-04-29  4:54           ` Daniel Axtens
2019-04-30  5:15           ` Andrew Donnellan
2019-04-30  5:15             ` Andrew Donnellan
2019-04-29 22:56   ` Matthew Garrett
2019-05-02 21:07     ` James Morris
2019-05-02 21:15       ` Matthew Garrett
2019-05-02 23:19         ` James Morris
2019-05-03  0:34           ` Andy Lutomirski [this message]
2019-04-04  0:32 ` [PATCH V32 02/27] Enforce module signatures if the kernel is locked down Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 03/27] Restrict /dev/{mem,kmem,port} when " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 04/27] kexec_load: Disable at runtime if " Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 05/27] Copy secure_boot flag in boot params across kexec reboot Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 06/27] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 07/27] kexec_file: Restrict at runtime if the kernel is locked down Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 08/27] hibernate: Disable when " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 09/27] uswsusp: " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 10/27] PCI: Lock down BAR access " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 11/27] x86: Lock down IO port " Matthew Garrett
2019-04-04  7:49   ` Thomas Gleixner
2019-04-04  0:32 ` [PATCH V32 12/27] x86/msr: Restrict MSR " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 13/27] ACPI: Limit access to custom_method " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 14/27] acpi: Ignore acpi_rsdp kernel param when the kernel has been " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 15/27] acpi: Disable ACPI table override if the kernel is " Matthew Garrett
2019-04-04  0:32   ` Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 16/27] Prohibit PCMCIA CIS storage when " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 17/27] Lock down TIOCSSERIAL Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 18/27] Lock down module params that specify hardware parameters (eg. ioport) Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 19/27] x86/mmiotrace: Lock down the testmmiotrace module Matthew Garrett
2019-04-04  1:33   ` Steven Rostedt
2019-04-04  7:47   ` Thomas Gleixner
2019-04-04  0:32 ` [PATCH V32 20/27] Lock down /proc/kcore Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 21/27] Lock down tracing and perf kprobes when in confidentiality mode Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 22/27] bpf: Restrict bpf when kernel lockdown is " Matthew Garrett
2019-04-30 19:19   ` Jann Horn
2019-04-04  0:32 ` [PATCH V32 23/27] Lock down perf when " Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 24/27] kexec: Allow kexec_file() with appropriate IMA policy when locked down Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 25/27] lockdown: Print current->comm in restriction messages Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 26/27] debugfs: Restrict debugfs when the kernel is locked down Matthew Garrett
2019-04-04  0:32 ` [PATCH V32 27/27] tracefs: Restrict tracefs " Matthew Garrett
2019-04-04 13:39   ` Steven Rostedt
2019-04-04 20:09     ` Matthew Garrett

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