Messages in this thread | | | From | "Jason A. Donenfeld" <> | Date | Fri, 23 Sep 2022 13:53:21 +0200 | Subject | Re: [PATCH 2/2] m68k: virt: generate new RNG seed on reboot |
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Hi Geert,
On Fri, Sep 23, 2022 at 1:30 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: > > +static struct bi_record *rng_seed_record; > > This can be const... > > memzero_explicit((void *)data, len + 2); > > + /* Store a reference to be filled in on reboot. */ > > + rng_seed_record = (void *)record; > > ... so this cast can be dropped.
Will do.
> > > + > > static void virt_reset(void) > > { > > void __iomem *base = (void __iomem *)virt_bi_data.ctrl.mmio; > > > > + if (rng_seed_record && rng_seed_record->size > sizeof(*rng_seed_record) + 2) { > > + u16 len = rng_seed_record->size - sizeof(*rng_seed_record) - 2; > > + get_random_bytes((u8 *)rng_seed_record->data + 2, len); > > + *(u16 *)rng_seed_record->data = len; > > Wouldn't it be simpler to just use the existing length? > > if (rnd_seed_record) { > u16 len = be16_to_cpup(data); > get_random_bytes((u8 *)rng_seed_record->data + 2, len); > }
No, that would not work. len is 0 there, since we zero out the bytes after use for forward secrecy, and we zero out the length, so that we don't wind up feeding it zeros.
> > However, I have my doubts this will actually work. Was this tested? > The bootinfo is passed from userspace, usually by reading > /proc/bootinfo, and adapting it where needed. > So I think you should implement this in kexec-tools instead.
Yes, this was tested. This is to handle the reboot case, just as the commit subject says. Specifically, calling `reboot(RB_AUTOBOOT);`.
It does *not* handle kexec. For that, indeed, kexec-tools needs to be augmented, but that's a separate patch that doesn't need to interact with this one.
The way I tested this is by having my initramfs just call `reboot(RB_AUTOBOOT);`, and having add_bootloader_randomness() print its contents to the console. I checked that it was both present and different every time.
I'll send a v2 with that const fix.
Jason
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