[PATCH V34 05/29] Restrict /dev/{mem,kmem,port} when the kernel is locked down
From: Matthew Garrett <hidden>
Date: 2019-06-22 00:04:18
Also in:
linux-security-module, lkml
Subsystem:
char and misc drivers, lockdown security module, security subsystem, the rest · Maintainers:
Arnd Bergmann, Greg Kroah-Hartman, Nicolas Bouchinet, Xiu Jianfeng, Paul Moore, James Morris, "Serge E. Hallyn", Linus Torvalds
From: Matthew Garrett <mjg59@srcf.ucam.org> Allowing users to read and write to core kernel memory makes it possible for the kernel to be subverted, avoiding module loading restrictions, and also to steal cryptographic information. Disallow /dev/mem and /dev/kmem from being opened this when the kernel has been locked down to prevent this. Also disallow /dev/port from being opened to prevent raw ioport access and thus DMA from being used to accomplish the same thing. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Matthew Garrett <redacted> Cc: x86@kernel.org --- drivers/char/mem.c | 6 +++++- include/linux/security.h | 1 + security/lockdown/lockdown.c | 1 + 3 files changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index b08dc50f9f26..93c02493f0fa 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c@@ -29,8 +29,8 @@ #include <linux/export.h> #include <linux/io.h> #include <linux/uio.h> - #include <linux/uaccess.h> +#include <linux/security.h> #ifdef CONFIG_IA64 # include <linux/efi.h>
@@ -786,6 +786,10 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig) static int open_port(struct inode *inode, struct file *filp) { + int ret = security_locked_down(LOCKDOWN_DEV_MEM); + + if (ret) + return ret; return capable(CAP_SYS_RAWIO) ? 0 : -EPERM; }
diff --git a/include/linux/security.h b/include/linux/security.h
index 46d85cd63b06..200175c8605a 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h@@ -83,6 +83,7 @@ enum lsm_event { enum lockdown_reason { LOCKDOWN_NONE, LOCKDOWN_MODULE_SIGNATURE, + LOCKDOWN_DEV_MEM, LOCKDOWN_INTEGRITY_MAX, LOCKDOWN_CONFIDENTIALITY_MAX, };
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 25a3a5b0aa9c..565c87451f0f 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c@@ -19,6 +19,7 @@ static enum lockdown_reason kernel_locked_down; static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = { [LOCKDOWN_NONE] = "none", [LOCKDOWN_MODULE_SIGNATURE] = "unsigned module loading", + [LOCKDOWN_DEV_MEM] = "/dev/mem,kmem,port", [LOCKDOWN_INTEGRITY_MAX] = "integrity", [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality", };
--
2.22.0.410.gd8fdbe21b5-goog