linux-kernel - Re: [PATCH 02/38] Annotate hardware config module parameters in arch/x86/mm/

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Date:   Wed, 5 Apr 2017 13:35:37 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     David Howells <dhowells@...hat.com>
Cc:     linux-kernel@...r.kernel.org, gnomes@...rguk.ukuu.org.uk,
        gregkh@...uxfoundation.org, nouveau@...ts.freedesktop.org,
        x86@...nel.org, linux-security-module@...r.kernel.org,
        keyrings@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 02/38] Annotate hardware config module parameters in
 arch/x86/mm/

On Wed, 05 Apr 2017 17:57:08 +0100
David Howells <dhowells@...hat.com> wrote:

> When the kernel is running in secure boot mode, we lock down the kernel to
> prevent userspace from modifying the running kernel image.  Whilst this
> includes prohibiting access to things like /dev/mem, it must also prevent
> access by means of configuring driver modules in such a way as to cause a
> device to access or modify the kernel image.
> 
> To this end, annotate module_param* statements that refer to hardware
> configuration and indicate for future reference what type of parameter they
> specify.  The parameter parser in the core sees this information and can
> skip such parameters with an error message if the kernel is locked down.
> The module initialisation then runs as normal, but just sees whatever the
> default values for those parameters is.
> 
> Note that we do still need to do the module initialisation because some
> drivers have viable defaults set in case parameters aren't specified and
> some drivers support automatic configuration (e.g. PNP or PCI) in addition
> to manually coded parameters.
> 
> This patch annotates drivers in arch/x86/mm/.
> 
> Suggested-by: Alan Cox <gnomes@...rguk.ukuu.org.uk>
> Signed-off-by: David Howells <dhowells@...hat.com>

Acked-by: Steven Rostedt (VMware) <rostedt@...dmis.org>

-- Steve

> cc: Ingo Molnar <mingo@...nel.org>
> cc: Thomas Gleixner <tglx@...utronix.de>
> cc: "H. Peter Anvin" <hpa@...or.com>
> cc: x86@...nel.org
> cc: linux-kernel@...r.kernel.org
> cc: nouveau@...ts.freedesktop.org
> ---
> 
>  arch/x86/mm/testmmiotrace.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/testmmiotrace.c b/arch/x86/mm/testmmiotrace.c
> index 38868adf07ea..f6ae6830b341 100644
> --- a/arch/x86/mm/testmmiotrace.c
> +++ b/arch/x86/mm/testmmiotrace.c
> @@ -9,7 +9,7 @@
>  #include <linux/mmiotrace.h>
>  
>  static unsigned long mmio_address;
> -module_param(mmio_address, ulong, 0);
> +module_param_hw(mmio_address, ulong, iomem, 0);
>  MODULE_PARM_DESC(mmio_address, " Start address of the mapping of 16 kB "
>  				"(or 8 MB if read_far is non-zero).");
>