From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Rafael J. Wysocki" Subject: Re: [PATCH V40 14/29] ACPI: Limit access to custom_method when the kernel is locked down Date: Wed, 21 Aug 2019 00:07:10 +0200 Message-ID: <2669800.DxYg3DGudY@kreacher> References: <20190820001805.241928-1-matthewgarrett@google.com> <20190820001805.241928-15-matthewgarrett@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <20190820001805.241928-15-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, linux-api@vger.kernel.org, Matthew Garrett , Matthew Garrett , David Howells , Kees Cook , linux-acpi@vger.kernel.org List-Id: linux-api@vger.kernel.org On Tuesday, August 20, 2019 2:17:50 AM CEST Matthew Garrett wrote: > From: Matthew Garrett > > custom_method effectively allows arbitrary access to system memory, making > it possible for an attacker to circumvent restrictions on module loading. > Disable it if the kernel is locked down. > > Signed-off-by: Matthew Garrett > Signed-off-by: David Howells > Reviewed-by: Kees Cook > cc: linux-acpi@vger.kernel.org > Signed-off-by: James Morris Acked-by: Rafael J. Wysocki > --- > drivers/acpi/custom_method.c | 6 ++++++ > include/linux/security.h | 1 + > security/lockdown/lockdown.c | 1 + > 3 files changed, 8 insertions(+) > > diff --git a/drivers/acpi/custom_method.c b/drivers/acpi/custom_method.c > index b2ef4c2ec955..7031307becd7 100644 > --- a/drivers/acpi/custom_method.c > +++ b/drivers/acpi/custom_method.c > @@ -9,6 +9,7 @@ > #include > #include > #include > +#include > > #include "internal.h" > > @@ -29,6 +30,11 @@ static ssize_t cm_write(struct file *file, const char __user * user_buf, > > struct acpi_table_header table; > acpi_status status; > + int ret; > + > + ret = security_locked_down(LOCKDOWN_ACPI_TABLES); > + if (ret) > + return ret; > > if (!(*ppos)) { > /* parse the table header to get the table length */ > diff --git a/include/linux/security.h b/include/linux/security.h > index 010637a79eac..390e39395112 100644 > --- a/include/linux/security.h > +++ b/include/linux/security.h > @@ -110,6 +110,7 @@ enum lockdown_reason { > LOCKDOWN_PCI_ACCESS, > LOCKDOWN_IOPORT, > LOCKDOWN_MSR, > + LOCKDOWN_ACPI_TABLES, > LOCKDOWN_INTEGRITY_MAX, > LOCKDOWN_CONFIDENTIALITY_MAX, > }; > diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c > index b1c1c72440d5..6d44db0ddffa 100644 > --- a/security/lockdown/lockdown.c > +++ b/security/lockdown/lockdown.c > @@ -25,6 +25,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { > [LOCKDOWN_PCI_ACCESS] = "direct PCI access", > [LOCKDOWN_IOPORT] = "raw io port access", > [LOCKDOWN_MSR] = "raw MSR access", > + [LOCKDOWN_ACPI_TABLES] = "modifying ACPI tables", > [LOCKDOWN_INTEGRITY_MAX] = "integrity", > [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", > }; >