linux-kernel - Re: [PATCH][RESEND] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed

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Date:   Wed, 3 Feb 2021 10:54:23 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Timur Tabi <timur@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        linux-kernel@...r.kernel.org, vbabka@...e.cz, linux-mm@...ck.org,
        willy@...radead.org, akpm@...ux-foundation.org,
        torvalds@...ux-foundation.org, roman.fietze@...na.com,
        keescook@...omium.org, john.ogness@...utronix.de,
        akinobu.mita@...il.com
Subject: Re: [PATCH][RESEND] lib/vsprintf: make-printk-non-secret printks all
 addresses as unhashed

On Tue 2021-02-02 15:36:33, Timur Tabi wrote:
> If the make-printk-non-secret command-line parameter is set, then
> printk("%p") will print addresses as unhashed.  This is useful for
> debugging purposes.
> 
> A large warning message is displayed if this option is enabled,
> because unhashed addresses, while useful for debugging, exposes
> kernel addresses which can be a security risk.
> 
> Signed-off-by: Timur Tabi <timur@...nel.org>
> ---
>  lib/vsprintf.c | 34 ++++++++++++++++++++++++++++++++--
>  1 file changed, 32 insertions(+), 2 deletions(-)

Please, add also entry into
Documentation/admin-guide/kernel-parameters.txt.

If we agree that the parameter is acceptable then let's make
it properly.

> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 3b53c73580c5..b9f87084afb0 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -2090,6 +2090,30 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
>  	return widen_string(buf, buf - buf_start, end, spec);
>  }
>  
> +/* Disable pointer hashing if requested */
> +static bool debug_never_hash_pointers __ro_after_init;
> +
> +static int __init debug_never_hash_pointers_enable(char *str)
> +{
> +	debug_never_hash_pointers = true;
> +	pr_warn("**********************************************************\n");
> +	pr_warn("**   NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE   **\n");
> +	pr_warn("**                                                      **\n");
> +	pr_warn("** All pointers that are printed to the console will    **\n");
> +	pr_warn("** be printed as unhashed.                              **\n");
> +	pr_warn("**                                                      **\n");
> +	pr_warn("** Kernel memory addresses are exposed, which may       **\n");
> +	pr_warn("** compromise security on your system.                  **\n");
> +	pr_warn("**                                                      **\n");
> +	pr_warn("** If you see this message and you are not debugging    **\n");
> +	pr_warn("** the kernel, report this immediately to your vendor!  **\n");

It is a boot parameter. So it should be "system administrtor" instead
of vendor.

Otherwise, it looks good to me.

Best Regards,
Petr