linux-kernel - Re: [PATCH v3] module: Allow to disable modsign in kernel cmdline

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Date:   Tue, 28 Apr 2020 08:35:22 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
Cc:     jeyu@...nel.org, corbet@....net, rdunlap@...radead.org,
        mchehab+samsung@...nel.org, tglx@...utronix.de,
        akpm@...ux-foundation.org, pawan.kumar.gupta@...ux.intel.com,
        jgross@...e.com, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH v3] module: Allow to disable modsign in kernel cmdline

On Tue, Apr 28, 2020 at 02:00:08PM +0800, Tianjia Zhang wrote:
> This option allows to disable modsign completely at the beginning,
> and turn off by set the kernel cmdline `no_modsig_enforce` when
> `CONFIG_MODULE_SIG_FORCE` is enabled.
> 
> Yet another change allows to always show the current status of
> modsign through `/sys/module/module/parameters/sig_enforce`.
> 
> Signed-off-by: Jia Zhang <zhang.jia@...ux.alibaba.com>
> Signed-off-by: Tianjia Zhang <tianjia.zhang@...ux.alibaba.com>
> ---
> 
> v3 change:
>   Beautify the document description according to the recommendation.
> 
> v2 change:
>   document this new option.
> 
>  Documentation/admin-guide/kernel-parameters.txt | 6 ++++++
>  kernel/module.c                                 | 8 ++++++++
>  2 files changed, 14 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 7bc83f3d9bdf..b30f013fb8c5 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3190,6 +3190,12 @@
>  	noirqdebug	[X86-32] Disables the code which attempts to detect and
>  			disable unhandled interrupt sources.
>  
> +	no_modsig_enforce
> +			[KNL] When CONFIG_MODULE_SIG_FORCE is set, this option
> +			allows to disable modsign completely at the beginning.
> +			This means that modules without (valid) signatures will
> +			be loaded successfully.
> +

So now we have module.sig_enforce and this one?  That feels really
confusing, why can't you just use the existing option?

And why would you want to allow the bootloader to override a kernel
build option like this?  That feels risky.

thanks,

greg k-h