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Date: Sat, 30 Dec 2017 12:39:17 -0800
From: Randy Dunlap <rdunlap@...radead.org>
To: Dan Aloni <dan@...nelim.com>, linux-kernel@...r.kernel.org,
 kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH 3/5] kernel/printk: allow kmsg to be encrypted using
 public key encryption

On 12/30/2017 09:58 AM, Dan Aloni wrote:
> From: Dan Aloni <dan@...nelim.com>
> 
> This commit enables the kernel to encrypt the free-form text that
> is generated by printk() before it is brought up to `dmesg` in
> userspace.
> 
> The encryption is made using one of the trusted public keys which
> are kept built-in inside the kernel. These keys are presently
> also used for verifying kernel modules and userspace-supplied
> firmwares.
> 
> Signed-off-by: Dan Aloni <dan@...nelim.com>
> ---
>  include/uapi/linux/kmsg.h |  18 ++
>  init/Kconfig              |  10 ++
>  kernel/printk/printk.c    | 422 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 450 insertions(+)
>  create mode 100644 include/uapi/linux/kmsg.h
> 
> diff --git a/include/uapi/linux/kmsg.h b/include/uapi/linux/kmsg.h
> new file mode 100644
> index 000000000000..ae74f026d727
> --- /dev/null
> +++ b/include/uapi/linux/kmsg.h
> @@ -0,0 +1,18 @@
> +#ifndef _LINUX_UAPI_KMSG_H
> +#define _LINUX_UAPI_KMSG_H
> +
> +#include <linux/ioctl.h>
> +#include <linux/types.h>
> +
> +struct kmsg_ioctl_get_encrypted_key {
> +	void __user *output_buffer;
> +	__u64 buffer_size;
> +	__u64 key_size;
> +};
> +
> +#define KMSG_IOCTL_BASE 0x42
> +
> +#define KMSG_IOCTL__GET_ENCRYPTED_KEY  _IOWR(KMSG_IOCTL_BASE, 0xe1, \
> +	    struct kmsg_ioctl_get_encrypted_key)
> +

The ioctl info needs to be added to Documentation/ioctl/ioctl-number.txt.
BTW, 0x42 == 'B', with number 0xe1, conflicts with advanced bbus, whatever
that is.  But at least it should be added to the doc file.

> +#endif /* _LINUX_DN_H */

> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index b9006617710f..c50b9cb60b82 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c

> @@ -744,12 +755,33 @@ static ssize_t msg_print_ext_body(char *buf, size_t size,
>  	return p - buf;
>  }
>  
> +#ifdef CONFIG_KMSG_ENCRYPTION
> +static int __ro_after_init kmsg_encrypt = 1;
> +static int __init control_kmsg_encrypt(char *str)
> +{
> +	get_option(&str, &kmsg_encrypt);
> +	return 0;
> +}
> +__setup("kmsg.encrypt=", control_kmsg_encrypt);

See comment in the documentation patch:  please change the parameter name (no dot).


-- 
~Randy

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