efistub: EFI_RNG_PROTOCOL on Dell Inc. Latitude 7390

From: Dominik Brodowski <linux@dominikbrodowski.net>
To: Ard Biesheuvel <ard.biesheuvel@linaro.org>, mario.limonciello@dell.com
Cc: linux-efi@vger.kernel.org
Subject: efistub: EFI_RNG_PROTOCOL on Dell Inc. Latitude 7390
Date: Mon, 28 Oct 2019 08:20:36 +0100	[thread overview]
Message-ID: <20191028072036.GA113601@owl.dominikbrodowski.net> (raw)
In-Reply-To: <20191005113753.GA77634@light.dominikbrodowski.net>

Ard, Mario,

in theory, invoking EFI_RNG_PROTOCOL on a Dell Inc. Latitude 7390/09386V,
BIOS 1.9.2 04/03/2019, should work fine as the system provides EFI v2.60.
Using my patch from a few weeks ago[1], efi_random_get_seed() is called from
arch/x86/boot/compressed/eboot.c::efi_main(). In efi_random_get_seed(), the
calls to

	status = efi_call_early(locate_protocol, &rng_proto, NULL,
				(void **)&rng);

and

	status = efi_call_early(allocate_pool, EFI_RUNTIME_SERVICES_DATA,
				sizeof(*seed) + EFI_RANDOM_SEED_SIZE,
				(void **)&seed);

succeed. However,

	status = rng->get_rng(rng, &rng_algo_raw, EFI_RANDOM_SEED_SIZE,
			      seed->bits);

returns EFI_INVALID_PARAMETER, though I can't see why one of these
parameters is invalid. When trying to use the default rng algorithm (by
modifying the test to "(status != EFI_SUCCESS)"),

		status = rng->get_rng(rng, NULL, EFI_RANDOM_SEED_SIZE,
				      seed->bits);

the call doesn't seem to return.

Any ideas?

Best,
	Dominik

[1] https://lore.kernel.org/lkml/20191005113753.GA77634@light.dominikbrodowski.net/