From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Rostedt Subject: Re: [PATCH V31 19/25] x86/mmiotrace: Lock down the testmmiotrace module Date: Wed, 27 Mar 2019 11:57:49 -0400 Message-ID: <20190327115749.5770a102@gandalf.local.home> References: <20190326182742.16950-1-matthewgarrett@google.com> <20190326182742.16950-20-matthewgarrett@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190326182742.16950-20-matthewgarrett@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Matthew Garrett Cc: jmorris@namei.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dhowells@redhat.com, linux-api@vger.kernel.org, luto@kernel.org, Thomas Gleixner , Matthew Garrett , Ingo Molnar , "H. Peter Anvin" , x86@kernel.org List-Id: linux-api@vger.kernel.org On Tue, 26 Mar 2019 11:27:35 -0700 Matthew Garrett wrote: > From: David Howells > > The testmmiotrace module shouldn't be permitted when the kernel is locked > down as it can be used to arbitrarily read and write MMIO space. This is > a runtime check rather than buildtime in order to allow configurations > where the same kernel may be run in both locked down or permissive modes > depending on local policy. > Acked-by: Steven Rostedt (VMware) I'm curious. Should there be a mode to lockdown the tracefs directory too? As that can expose addresses. -- Steve > Suggested-by: Thomas Gleixner > Signed-off-by: David Howells Signed-off-by: Matthew Garrett > cc: Thomas Gleixner > cc: Steven Rostedt > cc: Ingo Molnar > cc: "H. Peter Anvin" > cc: x86@kernel.org > --- > arch/x86/mm/testmmiotrace.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c > index f6ae6830b341..9e8ad665f354 100644 > --- a/arch/x86/mm/testmmiotrace.c > +++ b/arch/x86/mm/testmmiotrace.c > @@ -115,6 +115,9 @@ static int __init init(void) > { > unsigned long size = (read_far) ? (8 << 20) : (16 << 10); > > + if (kernel_is_locked_down("MMIO trace testing", LOCKDOWN_INTEGRITY)) > + return -EPERM; > + > if (mmio_address == 0) { > pr_err("you have to use the module argument mmio_address.\n"); > pr_err("DO NOT LOAD THIS MODULE UNLESS YOU REALLY KNOW WHAT YOU ARE DOING!\n");