[PATCH V37 14/29] ACPI: Limit access to custom_method when the kernel is locked down
From: Matthew Garrett <hidden>
Date: 2019-07-31 22:17:08
Also in:
linux-acpi, linux-security-module, lkml
Subsystem:
acpi, lockdown security module, security subsystem, the rest · Maintainers:
"Rafael J. Wysocki", Nicolas Bouchinet, Xiu Jianfeng, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
From: Matthew Garrett <mjg59@srcf.ucam.org> 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 <redacted> Signed-off-by: David Howells <dhowells@redhat.com> Reviewed-by: Kees Cook <redacted> cc: linux-acpi@vger.kernel.org --- 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 <linux/uaccess.h> #include <linux/debugfs.h> #include <linux/acpi.h> +#include <linux/security.h> #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 155ff026eca4..1c32522b3c5a 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 d99c0bee739d..ecb51b1a5c03 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", };
--
2.22.0.770.g0f2c4a37fd-goog