Re: [PATCH] x86: Parse CONFIG_CMDLINE in compressed kernel

[baskov]

On 2022-05-04 11:59, Borislav Petkov wrote:
> On Thu, Apr 07, 2022 at 05:40:14AM +0300, Baskov Evgeniy wrote:
> > CONFIG_CMDLINE_BOOL and CONFIG_CMDLINE_OVERRIDE was ignored
> > during options lookup in compressed kernel, including
> > earlyprintk option, so it was impossible to get earlyprintk
> > messages from that stage of boot process via command line
> > provided at compile time. Being able to enable earlyprintk
> > via compile-time option might be desirable for booting
> > on systems with broken UEFI command line arguments via EFISTUB.
> >
> > Parse CONFIG_CMDLINE-related options correctly in compressed
> > kernel code.
> >
> > Signed-off-by: Baskov Evgeniy <baskov@xxxxxxxxx>
> >
> > diff --git a/arch/x86/boot/compressed/cmdline.c 
> > b/arch/x86/boot/compressed/cmdline.c
> > index f1add5d85da9..dd8cbbe61dff 100644
> > --- a/arch/x86/boot/compressed/cmdline.c
> > +++ b/arch/x86/boot/compressed/cmdline.c
> > @@ -22,9 +22,49 @@ unsigned long get_cmd_line_ptr(void)
> >  }
> >  int cmdline_find_option(const char *option, char *buffer, int 
> > bufsize)
> >  {
> > -	return __cmdline_find_option(get_cmd_line_ptr(), option, buffer, 
> > bufsize);
> > +	int len = -1;
> > +	unsigned long cmdline_ptr;
> > +
> > +	/*
> > +	 * First try command line string provided by user,
> > +	 * then try command line string configured at comple time.
> > +	 * Skip first step if CONFIG_CMDLINE_OVERRIDE is enabled
> > +	 * and parse only compile time command line.
> > +	 */
> > +
> > +	if (!IS_ENABLED(CONFIG_CMDLINE_OVERRIDE)) {
> > +		cmdline_ptr = get_cmd_line_ptr();
> > +		len = __cmdline_find_option(cmdline_ptr, option,
> > +					    buffer, bufsize);
> > +	}
> > +
> > +#ifdef CONFIG_CMDLINE_BOOL
> > +	if (len < 0) {
> > +		cmdline_ptr = (unsigned long)CONFIG_CMDLINE;
> > +		len = __cmdline_find_option(cmdline_ptr, option,
> > +					    buffer, bufsize);
> > +	}
> > +#endif
>
> Do I see it correctly that all this logic boils down to returning the
> proper cmdline ptr and so you can do that once in get_cmd_line_ptr()
> instead of duplicating the ifdeffery?

Yes, it can be done by returning either concatenation of build-time
and run-time command line strings or only the build-time one,
depending on the kernel configuration.

Actually, it is implemented this way in arch/x86/kernel/setup.c.
I thought it's better to avoid imposing restrictions on kernel
command line length, but since it is already done, I guess,
I will do the same way in v2.

Thanks,
Baskov Evgeniy