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From: Daniel Axtens <dja@axtens.net>
To: Matthew Garrett <mjg59@google.com>,
	Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Cc: James Morris <jmorris@namei.org>,
	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>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	Michael Ellerman <mpe@ellerman.id.au>, cmr <cmr@informatik.wtf>
Subject: Re: [PATCH V32 01/27] Add the ability to lock down access to the running kernel image
Date: Mon, 29 Apr 2019 14:54:03 +1000	[thread overview]
Message-ID: <87tvehxvh0.fsf@dja-thinkpad.axtens.net> (raw)
In-Reply-To: <87wojdy8ro.fsf@dja-thinkpad.axtens.net>

Hi, 

>>> I'm thinking about whether we should lock down the powerpc xmon debug
>>> monitor - intuitively, I think the answer is yes if for no other reason
>>> than Least Astonishment, when lockdown is enabled you probably don't
>>> expect xmon to keep letting you access kernel memory.
>>
>> The original patchset contained a sysrq hotkey to allow physically
>> present users to disable lockdown, so I'm not super concerned about
>> this case - I could definitely be convinced otherwise, though.

So Mimi contacted me offlist and very helpfully provided me with a much
better and less confused justification for disabling xmon in lockdown:

On x86, physical presence (== console access) is a trigger to
disable/enable lockdown mode.

In lockdown mode, you're not supposed to be able to modify memory. xmon
allows you to modify memory, and therefore shouldn't be allowed in
lockdown.

So, if you can disable lockdown on the console that's probably OK, but
it should be specifically disabling lockdown, not randomly editing
memory with xmon.

Regards,
Daniel

WARNING: multiple messages have this Message-ID (diff)
From: Daniel Axtens <dja@axtens.net>
To: Matthew Garrett <mjg59@google.com>,
	Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Cc: Linux API <linux-api@vger.kernel.org>, cmr <cmr@informatik.wtf>,
	James Morris <jmorris@namei.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	David Howells <dhowells@redhat.com>,
	LSM List <linux-security-module@vger.kernel.org>,
	Andy Lutomirski <luto@kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH V32 01/27] Add the ability to lock down access to the running kernel image
Date: Mon, 29 Apr 2019 14:54:03 +1000	[thread overview]
Message-ID: <87tvehxvh0.fsf@dja-thinkpad.axtens.net> (raw)
In-Reply-To: <87wojdy8ro.fsf@dja-thinkpad.axtens.net>

Hi, 

>>> I'm thinking about whether we should lock down the powerpc xmon debug
>>> monitor - intuitively, I think the answer is yes if for no other reason
>>> than Least Astonishment, when lockdown is enabled you probably don't
>>> expect xmon to keep letting you access kernel memory.
>>
>> The original patchset contained a sysrq hotkey to allow physically
>> present users to disable lockdown, so I'm not super concerned about
>> this case - I could definitely be convinced otherwise, though.

So Mimi contacted me offlist and very helpfully provided me with a much
better and less confused justification for disabling xmon in lockdown:

On x86, physical presence (== console access) is a trigger to
disable/enable lockdown mode.

In lockdown mode, you're not supposed to be able to modify memory. xmon
allows you to modify memory, and therefore shouldn't be allowed in
lockdown.

So, if you can disable lockdown on the console that's probably OK, but
it should be specifically disabling lockdown, not randomly editing
memory with xmon.

Regards,
Daniel

  reply	other threads:[~2019-04-29  4:54 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 [this message]
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
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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