linux-kernel - Re: [PATCH] of: fdt: parse early params before adding bootloader randomness

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Message-ID: <Y2lBj1ZIdFRf9HdR@zx2c4.com>
Date:   Mon, 7 Nov 2022 18:34:07 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Rob Herring <robh@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        Frank Rowand <frowand.list@...il.com>
Subject: Re: [PATCH] of: fdt: parse early params before adding bootloader
 randomness

On Mon, Nov 07, 2022 at 11:28:20AM -0600, Rob Herring wrote:
> On Fri, Nov 4, 2022 at 8:46 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
> >
> > FDT is examined so early that it's before the first incidental call to
> > parse_early_param(). This is similar to EFI, except EFI actually added
> > an explicitly call to parse_early_param(). Let's do the same here, so
> > that specifying `random.trust_bootloader=0` is not ignored.
> >
> > Fixes: d97c68d178fb ("random: treat bootloader trust toggle the same way as cpu trust toggle")
> > Cc: Rob Herring <robh@...nel.org>
> > Cc: Frank Rowand <frowand.list@...il.com>
> > Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> > ---
> >  drivers/of/fdt.c | 3 +++
> >  1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > index 7b571a631639..6d959117fd4f 100644
> > --- a/drivers/of/fdt.c
> > +++ b/drivers/of/fdt.c
> > @@ -1195,6 +1195,9 @@ int __init early_init_dt_scan_chosen(char *cmdline)
> >
> >         rng_seed = of_get_flat_dt_prop(node, "rng-seed", &l);
> >         if (rng_seed && l > 0) {
> > +               /* Parse random.trust_bootloader if it's in command line. */
> > +               parse_early_param();
> 
> I don't think it's good that the timing of calling this is dependent
> on "rng-seed" being present or not. So perhaps move it up to after the
> cmdline is set.
> 
> Either way, the other issue is the cmdline is not necessarily fixed at
> this point with some architectures doing their own
> append/prepend/override of the cmdline. We can't seem to get common
> implementation there finished. I'm doubtful that corner case would
> actually be hit though.

Hm, yea. I'm actually now having second thoughts about this one too for
other reasons: FDT isn't the only arch that has this issue. It's also a
problem on x86 and m68k. Maybe the random.trust_bootloader toggle should
just go away, since already your bootloader can do whatever it wants to
the kernel it executes? Not sure; I'll think on it a bit I guess...

Jason