[PATCH 05/47][X] UBUNTU: SAUCE: (efi-lockdown) Restrict /dev/{mem, kmem, port} when the kernel is locked down

[Stefan Bader]

On 19.06.20 01:12, Seth Forshee wrote:
> From: Matthew Garrett <matthew.garrett at nebula.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1884159
> 
> 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 at nebula.com>
> Signed-off-by: David Howells <dhowells at redhat.com>
> Reviewed-by: "Lee, Chun-Yi" <jlee at suse.com>
> (backported from commit 2eada4c7af2d4e9522a47523d2a5106d96271cd9
>  git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
> Signed-off-by: Seth Forshee <seth.forshee at canonical.com>
> ---

This one appears odd, but I checked the reference and its the same.
Just hard to say it is doing what it claims from looking at the patch

>  drivers/char/mem.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/char/mem.c b/drivers/char/mem.c
> index 6ebe2b86d8eb..f41ad9aa5e0a 100644
> --- a/drivers/char/mem.c
> +++ b/drivers/char/mem.c
> @@ -8,6 +8,7 @@
>   *  Shared /dev/zero mmapping support, Feb 2000, Kanoj Sarcar <kanoj at sgi.com>
>   */
>  
> +#include <linux/module.h>
>  #include <linux/mm.h>
>  #include <linux/miscdevice.h>
>  #include <linux/slab.h>
> @@ -756,6 +757,8 @@ static loff_t memory_lseek(struct file *file, loff_t offset, int orig)
>  
>  static int open_port(struct inode *inode, struct file *filp)
>  {
> +	if (secure_modules())
> +		return -EPERM;
>  	return capable(CAP_SYS_RAWIO) ? 0 : -EPERM;
>  }
>  
> 


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