linux-kernel - Re: [PATCH] init: Handle bootloader head in kernel parameters

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Message-ID: <2025071130-mangle-ramrod-38ff@gregkh>
Date: Fri, 11 Jul 2025 13:06:55 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Huacai Chen <chenhuacai@...ngson.cn>
Cc: Huacai Chen <chenhuacai@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH] init: Handle bootloader head in kernel parameters

On Fri, Jul 11, 2025 at 06:24:55PM +0800, Huacai Chen wrote:
> BootLoader may pass a head such as "BOOT_IMAGE=/boot/vmlinuz-x.y.z" to
> kernel parameters. But this head is not recognized by the kernel so will
> be passed to user space. However, user space init program also doesn't
> recognized it.

Then why is it on the kernel command line if it is not recognized?

> KEXEC may also pass a head such as "kexec" on some architectures.

That's fine, kexec needs this.

> So the the best way is handle it by the kernel itself, which can avoid
> such boot warnings:
> 
> Kernel command line: BOOT_IMAGE=(hd0,1)/vmlinuz-6.x root=/dev/sda3 ro console=tty
> Unknown kernel command line parameters "BOOT_IMAGE=(hd0,1)/vmlinuz-6.x", will be passed to user space.

Why is this a problem?  Don't put stuff that is not needed on the kernel
command line :)

> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
>  init/main.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/init/main.c b/init/main.c
> index 225a58279acd..9e0a7e8913c0 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -545,6 +545,7 @@ static int __init unknown_bootoption(char *param, char *val,
>  				     const char *unused, void *arg)
>  {
>  	size_t len = strlen(param);
> +	const char *bootloader[] = { "BOOT_IMAGE", "kexec", NULL };

You need to document why these are ok to "swallow" and not warn for.


>  
>  	/* Handle params aliased to sysctls */
>  	if (sysctl_is_alias(param))
> @@ -552,6 +553,12 @@ static int __init unknown_bootoption(char *param, char *val,
>  
>  	repair_env_string(param, val);
>  
> +	/* Handle bootloader head */

Handle it how?

confused,

greg k-h