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Donenfeld" To: Rasmus Villemoes Cc: Rob Herring , devicetree@vger.kernel.org, linux-kernel@vger.kernel.org, Frank Rowand Subject: Re: [PATCH] of: fdt: parse early params before adding bootloader randomness Message-ID: References: <20221105014613.113503-1-Jason@zx2c4.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 18, 2022 at 09:33:53AM +0100, Rasmus Villemoes wrote: > On 07/11/2022 18.34, Jason A. Donenfeld wrote: > > 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 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 > >>> Cc: Frank Rowand > >>> Signed-off-by: Jason A. Donenfeld > >>> --- > >>> 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... > > Well, for the FDT case it least one could preserve the ability for the > bootloader to say "hey, here's a bunch of bytes, but I have reason to > believe they're not as random as you'd like" by setting a boolean > "rng-seed-is-crap" [pick a better name] property alongside the rng-seed > property. Then the kernel logic could be CONFIG_TRUST_BOOT_LOADER && > !of_get_bool("rng-seed-is-crap"). Currently, the only thing the > bootloader could do in that case is to just elide the rng-seed > completely (or set the not-actually-working cmdline flag). Yea I don't think we want to introduce that kind of complexity here. No more knobs :) Jason