Messages in this thread | | | Date | Tue, 17 May 2022 18:25:08 +0200 | From | Ahmad Fatoum <> | Subject | Re: [PATCH v10 2/7] KEYS: trusted: allow use of kernel RNG for key material |
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Hello Mimi,
[Cc'ing RNG maintainers in case they want to chime in]
On 17.05.22 17:52, Mimi Zohar wrote: > On Fri, 2022-05-13 at 16:57 +0200, Ahmad Fatoum wrote: >> static int __init init_trusted(void) >> { >> + int (*get_random)(unsigned char *key, size_t key_len); >> int i, ret = 0; >> >> for (i = 0; i < ARRAY_SIZE(trusted_key_sources); i++) { >> @@ -322,6 +333,28 @@ static int __init init_trusted(void) >> strlen(trusted_key_sources[i].name))) >> continue; >> >> + /* >> + * We always support trusted.rng="kernel" and "default" as >> + * well as trusted.rng=$trusted.source if the trust source >> + * defines its own get_random callback. >> + */ > > While TEE trusted keys support was upstreamed, there was a lot of > discussion about using kernel RNG. One of the concerns was lack of or > insuffiencent entropy during early boot on embedded devices. This > concern needs to be clearly documented in both Documentation/admin- > guide/kernel-parameters.txt and Documentation/security/keys/trusted- > encrypted.rst.
If a user decides to use kernel RNG for trusted keys, wait_for_random_bytes() called first thing in the used get_random_bytes_wait() will (quoting documentation) "wait for the input pool to be seeded and thus [is] guaranteed to supply cryptographically secure random numbers."
Does this address your concerns about Kernel RNG use?
Thanks, Ahmad
> > thanks, > > Mimi > >> + get_random = trusted_key_sources[i].ops->get_random; >> + if (trusted_rng && strcmp(trusted_rng, "default")) { >> + if (!strcmp(trusted_rng, "kernel")) { >> + get_random = kernel_get_random; >> + } else if (strcmp(trusted_rng, trusted_key_sources[i].name) || >> + !get_random) { >> + pr_warn("Unsupported RNG. Supported: kernel"); >> + if (get_random) >> + pr_cont(", %s", trusted_key_sources[i].name); >> + pr_cont(", default\n"); >> + return -EINVAL; >> + } >> + } >> + >> + if (!get_random) >> + get_random = kernel_get_random; >> + >> static_call_update(trusted_key_init, >> trusted_key_sources[i].ops->init); > >
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