Messages in this thread | | | Date | Fri, 23 Sep 2022 15:10:49 +0200 | From | Laurent Vivier <> | Subject | Re: [PATCH 2/2] m68k: virt: generate new RNG seed on reboot |
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Le 23/09/2022 à 14:50, Geert Uytterhoeven a écrit : > Hi Jason, > > On Fri, Sep 23, 2022 at 2:26 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote: >> On Fri, Sep 23, 2022 at 2:23 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote: >>>>>> + 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; >>> >>> Storing the length should use the proper cpu_to_be16 accessor. >> >> Okay, I'll do that for v2. >> >> (Simply out of curiosity, why? Isn't m68k always big endian and this >> is arch/ code?) > > Yes it is. But virt_parse_bootinfo() below already uses the right > accessor. > > BTW, I guess people thought the same about PowerPC? > Although I agree the probability of someone creating a little-endian > m68k clone in an FPGA or SkyWater project and trying to run Linux on > it quite low ;-) > >>>> 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. >>> >>> Are you sure the new kernel did receive the same randomness as prepared >>> by get_random_bytes()? I would expect it to just reboot into qemu, >>> reload the kernel from disk, and recreate a new bootinfo from scratch, >>> including generating a new random seed. >> >> Yes I'm sure. Without this patch, the new kernel sees the zeroed state. > > That's interesting. So QEMU preserves the old bootinfo, which is > AFAIK not guaranteed to be still available (that's why I added > save_bootinfo()). Perhaps that works because only memory starting > from a rounded-up value of _end will be used, and you're just lucky? > I'm wondering what else it preserves. It sure has to reload the > kernel image, as at least the data section will no longer contain the > initialization values after a reboot... > > Laurent? >
In QEMU the loader makes a copy of the kernel and the initrd and this copy is restored on a reset.
I don't think there is a mechanism in QEMU to save the BOOTINFO section, so I think it works by luck. I will check.
Thanks, Laurent
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