From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Garrett Subject: [PATCH V33 05/30] Restrict /dev/{mem,kmem,port} when the kernel is locked down Date: Thu, 20 Jun 2019 18:19:16 -0700 Message-ID: <20190621011941.186255-6-matthewgarrett@google.com> References: <20190621011941.186255-1-matthewgarrett@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <20190621011941.186255-1-matthewgarrett@google.com> Sender: linux-kernel-owner@vger.kernel.org To: jmorris@namei.org Cc: linux-security@vger.kernel.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, Matthew Garrett , David Howells , Matthew Garrett , x86@kernel.org List-Id: linux-api@vger.kernel.org From: Matthew Garrett 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 Signed-off-by: Matthew Garrett Cc: x86@kernel.org --- drivers/char/mem.c | 4 +++- include/linux/security.h | 1 + security/lockdown/lockdown.c | 1 + 3 files changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index b08dc50f9f26..1ee6cff43eea 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -29,8 +29,8 @@ #include #include #include - #include +#include #ifdef CONFIG_IA64 # include @@ -786,6 +786,8 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig) static int open_port(struct inode *inode, struct file *filp) { + if (security_is_locked_down(LOCKDOWN_DEV_MEM)) + return -EPERM; return capable(CAP_SYS_RAWIO) ? 0 : -EPERM; } diff --git a/include/linux/security.h b/include/linux/security.h index a7612b03b42a..034a8d54687f 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 08abd7e6609b..43a049b3b66a 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