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

[Huacai Chen <chenhuacai@kernel.org>]

Hi, Greg,

On Fri, Jul 11, 2025 at 7:06 PM Greg KH <gregkh@linuxfoundation.org> wrote:
>
> 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?
UEFI put it at the beginning of the command line, you can see it from
/proc/cmdline, both on x86 and LoongArch.

>
> > 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 :)
Both kernel and user space don't need it, and if it is passed to user
space then may cause some problems. For example, if there is
init=/bin/bash, then bash will crash with this parameter.

>
> >
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Huacai Chen <chenhuacai@loongson.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.
Because they are bootloader heads, not really a wrong parameter. We
only need a warning if there is a wrong parameter.

>
>
> >
> >       /* 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?
argv_init and envp_init arrays will be passed to userspace, so just
return early (before argv_init and envp_init handling) can avoid it
being passed.

Huacai

>
> confused,
>
> greg k-h