On Sat, 16 Apr 2022 at 00:31, Linus Walleij <linus.walleij@xxxxxxxxxx> wrote: > > To make the entropy pool a bit better we can toss in the > CID for eMMC and SD cards into it, usually the serial > number portion is at least unique. > > This does not count as improvement of the entropy but > in practice it makes it a bit more random to mix in these > numbers. > > Cc: Theodore Ts'o <tytso@xxxxxxx> > Cc: Jason A. Donenfeld <Jason@xxxxxxxxx> > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx> > --- > drivers/mmc/core/mmc.c | 7 +++++++ > drivers/mmc/core/sd.c | 7 +++++++ > 2 files changed, 14 insertions(+) > > diff --git a/drivers/mmc/core/mmc.c b/drivers/mmc/core/mmc.c > index e7ea45386c22..974d8a02b966 100644 > --- a/drivers/mmc/core/mmc.c > +++ b/drivers/mmc/core/mmc.c > @@ -12,6 +12,7 @@ > #include <linux/slab.h> > #include <linux/stat.h> > #include <linux/pm_runtime.h> > +#include <linux/random.h> > #include <linux/sysfs.h> > > #include <linux/mmc/host.h> > @@ -1673,6 +1674,12 @@ static int mmc_init_card(struct mmc_host *host, u32 ocr, > err = mmc_decode_cid(card); > if (err) > goto free_card; > + /* > + * Add card ID (cid) data to the entropy pool. > + * It doesn't matter that not all of it is unique, > + * it's just bonus entropy. > + */ > + add_device_randomness(&card->cid, sizeof(card->cid)); We can move this into mmc_decode_cid() instead, to avoid open coding. Moreover, this would make it work for SDIO/SD combo cards too, whatever that matters. One thing though, what is the typical execution time to do this? Probably negligible, but as this may be a card that holds the rootfs, it could delay the boot to be completed. [...] Kind regards Uffe
