linux-kernel - Re: [PATCH V2] init: Handle bootloader identifier in kernel parameters

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Message-ID: <2025072056-gambling-ranger-5b0f@gregkh>
Date: Sun, 20 Jul 2025 13:10:48 +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 V2] init: Handle bootloader identifier in kernel
 parameters

On Sun, Jul 20, 2025 at 06:55:09PM +0800, Huacai Chen wrote:
> BootLoader (Grub, LILO, etc) may pass an identifier such as "BOOT_IMAGE=
> /boot/vmlinuz-x.y.z" to kernel parameters. But these identifiers are not
> recognized by the kernel itself so will be passed to user space. However
> user space init program also doesn't recognized it.
> 
> KEXEC may also pass an identifier such as "kexec" on some architectures.
> 
> We cannot change BootLoader's behavior, because this behavior exists for
> many years, and there are already user space programs search BOOT_IMAGE=
> in /proc/cmdline to obtain the kernel image locations:
> 
> https://github.com/linuxdeepin/deepin-ab-recovery/blob/master/util.go
> (search getBootOptions)
> https://github.com/linuxdeepin/deepin-ab-recovery/blob/master/main.go
> (search getKernelReleaseWithBootOption)
> 
> So the the best way is handle (ignore) it by the kernel itself, which
> can avoid such boot warnings (if we use something like init=/bin/bash,
> bootloader identifier can even cause a crash):
> 
> 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.
> 
> Cc: stable@...r.kernel.org
> Signed-off-by: Huacai Chen <chenhuacai@...ngson.cn>
> ---
> V2: Update comments and commit messages.
> 
>  init/main.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/init/main.c b/init/main.c
> index 225a58279acd..c53863e5ad82 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 };

Where is this magic set of values now documented?  Each of these need to
be strongly documented as to why we are ignoring them and who is adding
them and why they can't be fixed for whatever reason.

thanks,

greg k-h