On 24 August 2018 at 22:46, Martin K. Petersen <martin.petersen@xxxxxxxxxx> wrote: > > Ard, > >> I'd prefer to handle this without help from userland. >> >> It shouldn't be too difficult to register a module notifier that only >> sets a flag (or the static key, even?), and to free and re-allocate >> the crc_t10dif transform if the flag is set. > > Something like this proof of concept? > > diff --git a/lib/crc-t10dif.c b/lib/crc-t10dif.c > index 1ad33e555805..87d0e8f0794a 100644 > --- a/lib/crc-t10dif.c > +++ b/lib/crc-t10dif.c > @@ -15,10 +15,50 @@ > #include <linux/init.h> > #include <crypto/hash.h> > #include <linux/static_key.h> > +#include <linux/notifier.h> > > static struct crypto_shash *crct10dif_tfm; > static struct static_key crct10dif_fallback __read_mostly; > > +static void crc_t10dif_print(void) > +{ > + if (static_key_false(&crct10dif_fallback)) > + pr_info("CRC T10 DIF calculated using library function\n"); > + else > + pr_info("CRC T10 DIF calculated using crypto hash %s\n", > + crypto_tfm_alg_driver_name(crypto_shash_tfm(crct10dif_tfm))); > +} > + > +static int crc_t10dif_rehash(struct notifier_block *self, unsigned long val, void *data) > +{ > +#ifdef CONFIG_MODULES > + struct module *mod = data; > + > + if (val != MODULE_STATE_LIVE || > + strncmp(mod->name, "crct10dif", strlen("crct10dif"))) > + return 0; > + > + /* Fall back to library function while we replace the tfm */ > + static_key_slow_inc(&crct10dif_fallback); > + > + crypto_free_shash(crct10dif_tfm); > + crct10dif_tfm = crypto_alloc_shash("crct10dif", 0, 0); > + if (IS_ERR(crct10dif_tfm)) { > + crct10dif_tfm = NULL; > + goto out; > + } > + > + static_key_slow_dec(&crct10dif_fallback); > +out: > + crc_t10dif_print(); > + return 0; > +#endif /* CONFIG_MODULES */ > +} > + > +static struct notifier_block crc_t10dif_nb = { > + .notifier_call = crc_t10dif_rehash, > +}; > + > __u16 crc_t10dif_update(__u16 crc, const unsigned char *buffer, size_t len) > { > struct { > @@ -49,16 +90,21 @@ EXPORT_SYMBOL(crc_t10dif); > > static int __init crc_t10dif_mod_init(void) > { > + register_module_notifier(&crc_t10dif_nb); > + > crct10dif_tfm = crypto_alloc_shash("crct10dif", 0, 0); > if (IS_ERR(crct10dif_tfm)) { > static_key_slow_inc(&crct10dif_fallback); > crct10dif_tfm = NULL; > } > + > + crc_t10dif_print(); > return 0; > } > > static void __exit crc_t10dif_mod_fini(void) > { > + unregister_module_notifier(&crc_t10dif_nb); > crypto_free_shash(crct10dif_tfm); > } > This looks like it should work, yes. It does rely on the module name to start with 'crct10dif' but I guess that is reasonable, and matches the current state on all architectures. Anyone care to boot test this? Jeffrey?