From: Matthew Garrett Date: Wed, 8 Nov 2017 15:11:32 +0000 Subject: [05/29] Restrict /dev/{mem,kmem,port} when the kernel is locked down Origin: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/commit?id=8214bb0d847928bf08a7d8475f84c06541c5a352 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: Matthew Garrett Signed-off-by: David Howells Reviewed-by: "Lee, Chun-Yi" --- drivers/char/mem.c | 2 ++ 1 file changed, 2 insertions(+) Index: linux/drivers/char/mem.c =================================================================== --- linux.orig/drivers/char/mem.c +++ linux/drivers/char/mem.c @@ -807,6 +807,8 @@ static loff_t memory_lseek(struct file * static int open_port(struct inode *inode, struct file *filp) { + if (kernel_is_locked_down("/dev/mem,kmem,port")) + return -EPERM; return capable(CAP_SYS_RAWIO) ? 0 : -EPERM; }