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Date: Thu, 9 Nov 2017 17:31:15 +0000 From: David Howells <dhowells@...hat.com> To: linux-security-module@...r.kernel.org Cc: gnomes@...rguk.ukuu.org.uk, linux-efi@...r.kernel.org, dhowells@...hat.com, linux-kernel@...r.kernel.org, jforbes@...hat.com Subject: [PATCH 05/30] Restrict /dev/{mem, kmem, port} when the kernel is locked down From: Matthew Garrett <matthew.garrett@...ula.com> 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 <matthew.garrett@...ula.com> Signed-off-by: David Howells <dhowells@...hat.com> Reviewed-by: "Lee, Chun-Yi" <jlee@...e.com> --- drivers/char/mem.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/char/mem.c b/drivers/char/mem.c index 593a8818aca9..0ce5ac0a5c6b 100644 --- a/drivers/char/mem.c +++ b/drivers/char/mem.c @@ -762,6 +762,8 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig) static int open_port(struct inode *inode, struct file *filp) { + if (kernel_is_locked_down("/dev/mem,kmem,port")) + return -EPERM; return capable(CAP_SYS_RAWIO) ? 0 : -EPERM; }
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