Hi Geert,
On Fri, Sep 23, 2022 at 1:30 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> 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
