[RFC] random: UEFI RNG input is bootloader randomness

[RFC] random: UEFI RNG input is bootloader randomness

[Dominik Brodowski]

Depending on RANDOM_TRUST_BOOTLOADER, bootloader-provided randomness
is credited as entropy. As the UEFI seeding entropy pool is seeded by
the UEFI firmware/bootloader, add its content as bootloader randomness.

Note that this UEFI (v2.4 or newer) feature is currently only
implemented for EFI stub booting on ARM, and further note that
RANDOM_TRUST_BOOTLOADER must only be enabled if there indeed is
sufficient trust in the bootloader _and_ its source of randomness.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Hsin-Yi Wang <hsinyi@chromium.org>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: Rob Herring <robh@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Lee, Chun-Yi <joeyli.kernel@gmail.com>

---

Untested patch, as efi_random_get_seed() is only hooked up on ARM,
and the firmware on my old x86 laptop only has UEFI v2.31 anyway.

Thanks,
	Dominik

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 8f1ab04f6743..db0bffce754e 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -545,7 +545,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
 					      sizeof(*seed) + size);
 			if (seed != NULL) {
 				pr_notice("seeding entropy pool\n");
-				add_device_randomness(seed->bits, seed->size);
+				add_bootloader_randomness(seed->bits, seed->size);
 				early_memunmap(seed, sizeof(*seed) + size);
 			} else {
 				pr_err("Could not map UEFI random seed!\n");

Re: [RFC] random: UEFI RNG input is bootloader randomness

[Kees Cook]

On Sat, Sep 28, 2019 at 12:14:28PM +0200, Dominik Brodowski wrote:
> Depending on RANDOM_TRUST_BOOTLOADER, bootloader-provided randomness
> is credited as entropy. As the UEFI seeding entropy pool is seeded by
> the UEFI firmware/bootloader, add its content as bootloader randomness.
> 
> Note that this UEFI (v2.4 or newer) feature is currently only
> implemented for EFI stub booting on ARM, and further note that
> RANDOM_TRUST_BOOTLOADER must only be enabled if there indeed is
> sufficient trust in the bootloader _and_ its source of randomness.
> 
> Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> Cc: Stephen Boyd <swboyd@chromium.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Lee, Chun-Yi <joeyli.kernel@gmail.com>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> 
> ---
> 
> Untested patch, as efi_random_get_seed() is only hooked up on ARM,
> and the firmware on my old x86 laptop only has UEFI v2.31 anyway.
> 
> Thanks,
> 	Dominik
> 
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 8f1ab04f6743..db0bffce754e 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -545,7 +545,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
>  					      sizeof(*seed) + size);
>  			if (seed != NULL) {
>  				pr_notice("seeding entropy pool\n");
> -				add_device_randomness(seed->bits, seed->size);
> +				add_bootloader_randomness(seed->bits, seed->size);
>  				early_memunmap(seed, sizeof(*seed) + size);
>  			} else {
>  				pr_err("Could not map UEFI random seed!\n");

-- 
Kees Cook

Re: [RFC] random: UEFI RNG input is bootloader randomness

[Bhupesh Sharma]

On Sat, Sep 28, 2019 at 3:54 PM Dominik Brodowski
<linux@dominikbrodowski.net> wrote:
>
> Depending on RANDOM_TRUST_BOOTLOADER, bootloader-provided randomness
> is credited as entropy. As the UEFI seeding entropy pool is seeded by
> the UEFI firmware/bootloader, add its content as bootloader randomness.
>
> Note that this UEFI (v2.4 or newer) feature is currently only
> implemented for EFI stub booting on ARM, and further note that
> RANDOM_TRUST_BOOTLOADER must only be enabled if there indeed is
> sufficient trust in the bootloader _and_ its source of randomness.
>
> Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> Cc: Stephen Boyd <swboyd@chromium.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Lee, Chun-Yi <joeyli.kernel@gmail.com>
>
> ---
>
> Untested patch, as efi_random_get_seed() is only hooked up on ARM,
> and the firmware on my old x86 laptop only has UEFI v2.31 anyway.
>
> Thanks,
>         Dominik
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 8f1ab04f6743..db0bffce754e 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -545,7 +545,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
>                                               sizeof(*seed) + size);
>                         if (seed != NULL) {
>                                 pr_notice("seeding entropy pool\n");
> -                               add_device_randomness(seed->bits, seed->size);
> +                               add_bootloader_randomness(seed->bits, seed->size);
>                                 early_memunmap(seed, sizeof(*seed) + size);
>                         } else {
>                                 pr_err("Could not map UEFI random seed!\n");

Tested the patch on my arm64 board which support EFI_RNG_PROTOCOL
(i.e. EFI firmware acts as the entropy source) and has
'CONFIG_RANDOM_TRUST_BOOTLOADER=y', so:

Tested-by: Bhupesh Sharma <bhsharma@redhat.com>

Thanks.

Re: [RFC] random: UEFI RNG input is bootloader randomness

[Ard Biesheuvel]

On Sat, 28 Sep 2019 at 12:14, Dominik Brodowski
<linux@dominikbrodowski.net> wrote:
>
> Depending on RANDOM_TRUST_BOOTLOADER, bootloader-provided randomness
> is credited as entropy. As the UEFI seeding entropy pool is seeded by
> the UEFI firmware/bootloader, add its content as bootloader randomness.
>
> Note that this UEFI (v2.4 or newer) feature is currently only
> implemented for EFI stub booting on ARM, and further note that
> RANDOM_TRUST_BOOTLOADER must only be enabled if there indeed is
> sufficient trust in the bootloader _and_ its source of randomness.
>
> Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>
> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Cc: Hsin-Yi Wang <hsinyi@chromium.org>
> Cc: Stephen Boyd <swboyd@chromium.org>
> Cc: Rob Herring <robh@kernel.org>
> Cc: Theodore Ts'o <tytso@mit.edu>
> Cc: Lee, Chun-Yi <joeyli.kernel@gmail.com>
>
> ---
>
> Untested patch, as efi_random_get_seed() is only hooked up on ARM,
> and the firmware on my old x86 laptop only has UEFI v2.31 anyway.
>
> Thanks,
>         Dominik
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index 8f1ab04f6743..db0bffce754e 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -545,7 +545,7 @@ int __init efi_config_parse_tables(void *config_tables, int count, int sz,
>                                               sizeof(*seed) + size);
>                         if (seed != NULL) {
>                                 pr_notice("seeding entropy pool\n");
> -                               add_device_randomness(seed->bits, seed->size);
> +                               add_bootloader_randomness(seed->bits, seed->size);
>                                 early_memunmap(seed, sizeof(*seed) + size);
>                         } else {
>                                 pr_err("Could not map UEFI random seed!\n");

Thanks, I like this change. I'll get it queued up in efi/next.