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boot: remove random-seed-mode

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Now that the random seed is used on virtualized systems, there's no
point in having a random-seed-mode toggle switch. Let's just always
require it now, with the existing logic already being there to allow not
having it if EFI itself has an RNG. In other words, the logic for this
can now be automatic.
This commit is contained in:
Jason A. Donenfeld 2022-11-21 16:40:24 +01:00 committed by Luca Boccassi
parent a0c544ee09
commit 47b3e96647
7 changed files with 5 additions and 77 deletions
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8
docs/RANDOM_SEEDS.md
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@ -232,14 +232,6 @@ boot, in order to ensure the entropy pool is filled up quickly.
too), which should be safe even with FAT file system drivers built into
low-quality EFI firmwares.
If the system token is not desired but this seeding mechanism still is, OS
builders that know that they are not going to replicate the built image on
multiple systems may opt to turn off the 'system token' concept by setting
`random-seed-mode always` in the ESP's
[`/loader/loader.conf`](https://www.freedesktop.org/software/systemd/man/loader.conf.html)
file. If done, `systemd-boot` will use the random seed file even if no
system token is found in EFI variables.
4. A kernel command line option `systemd.random_seed=` may be used to pass in a
base64 encoded seed to initialize the kernel's entropy pool from during
early service manager initialization. This option is only safe in testing

19
man/loader.conf.xml
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@ -309,25 +309,6 @@ sign-efi-sig-list -c KEK.crt -k KEK.key db db.esl db.auth
encrypted drive to change. If PCR 4 is not measured, this setting can be disabled to speed
up booting into Windows.</para></listitem>
</varlistentry>
<varlistentry>
<term>random-seed-mode</term>
<listitem><para>Takes one of <literal>off</literal>, <literal>with-system-token</literal> and
<literal>always</literal>. If <literal>off</literal> no random seed data is read off the ESP, nor
passed to the OS. If <literal>with-system-token</literal> (the default)
<command>systemd-boot</command> will read a random seed from the ESP (from the file
<filename>/loader/random-seed</filename>) only if the <varname>LoaderSystemToken</varname> EFI
variable is set, and then derive the random seed to pass to the OS from the combination. If
<literal>always</literal> the boot loader will do so even if <varname>LoaderSystemToken</varname> is
not set. This mode is useful in environments where protection against OS image reuse is not a
concern, and the random seed shall be used even with no further setup in place. Use <command>bootctl
random-seed</command> to initialize both the random seed file in the ESP and the system token EFI
variable.</para>
<para>See <ulink url="https://systemd.io/RANDOM_SEEDS">Random Seeds</ulink> for further
information.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>

26
src/boot/efi/boot.c
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@ -97,7 +97,6 @@ typedef struct {
bool beep;
int64_t console_mode;
int64_t console_mode_efivar;
RandomSeedMode random_seed_mode;
} Config;
/* These values have been chosen so that the transitions the user sees could
@ -529,7 +528,6 @@ static void print_status(Config *config, char16_t *loaded_image_path) {
ps_bool(L" auto-firmware: %s\n", config->auto_firmware);
ps_bool(L" beep: %s\n", config->beep);
ps_bool(L" reboot-for-bitlocker: %s\n", config->reboot_for_bitlocker);
ps_string(L" random-seed-mode: %s\n", random_seed_modes_table[config->random_seed_mode]);
switch (config->secure_boot_enroll) {
case ENROLL_OFF:
@ -1273,27 +1271,6 @@ static void config_defaults_load_from_file(Config *config, char *content) {
}
continue;
}
if (streq8(key, "random-seed-mode")) {
if (streq8(value, "off"))
config->random_seed_mode = RANDOM_SEED_OFF;
else if (streq8(value, "with-system-token"))
config->random_seed_mode = RANDOM_SEED_WITH_SYSTEM_TOKEN;
else if (streq8(value, "always"))
config->random_seed_mode = RANDOM_SEED_ALWAYS;
else {
bool on;
err = parse_boolean(value, &on);
if (err != EFI_SUCCESS) {
log_error_stall(L"Error parsing 'random-seed-mode' config option: %a", value);
continue;
}
config->random_seed_mode = on ? RANDOM_SEED_ALWAYS : RANDOM_SEED_OFF;
}
continue;
}
}
}
@ -1584,7 +1561,6 @@ static void config_load_defaults(Config *config, EFI_FILE *root_dir) {
.auto_firmware = true,
.reboot_for_bitlocker = false,
.secure_boot_enroll = ENROLL_MANUAL,
.random_seed_mode = RANDOM_SEED_WITH_SYSTEM_TOKEN,
.idx_default_efivar = IDX_INVALID,
.console_mode = CONSOLE_MODE_KEEP,
.console_mode_efivar = CONSOLE_MODE_KEEP,
@ -2743,7 +2719,7 @@ EFI_STATUS efi_main(EFI_HANDLE image, EFI_SYSTEM_TABLE *sys_table) {
save_selected_entry(&config, entry);
/* Optionally, read a random seed off the ESP and pass it to the OS */
(void) process_random_seed(root_dir, config.random_seed_mode);
(void) process_random_seed(root_dir);
err = image_start(image, entry);
if (err != EFI_SUCCESS)

7
src/boot/efi/random-seed.c
View File

@ -116,7 +116,7 @@ static void validate_sha256(void) {
#endif
}
EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode) {
EFI_STATUS process_random_seed(EFI_FILE *root_dir) {
_cleanup_erase_ uint8_t random_bytes[DESIRED_SEED_SIZE], hash_key[HASH_VALUE_SIZE];
_cleanup_free_ struct linux_efi_random_seed *new_seed_table = NULL;
struct linux_efi_random_seed *previous_seed_table = NULL;
@ -135,9 +135,6 @@ EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode) {
validate_sha256();
if (mode == RANDOM_SEED_OFF)
return EFI_NOT_FOUND;
/* hash = LABEL || sizeof(input1) || input1 || ... || sizeof(inputN) || inputN */
sha256_init_ctx(&hash);
@ -188,7 +185,7 @@ EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode) {
* system, even when disk images are duplicated or swapped out. */
size = 0;
err = acquire_system_token(&system_token, &size);
if (mode != RANDOM_SEED_ALWAYS && (err != EFI_SUCCESS || size < DESIRED_SEED_SIZE) && !seeded_by_efi)
if ((err != EFI_SUCCESS || size < DESIRED_SEED_SIZE) && !seeded_by_efi)
return err;
sha256_process_bytes(&size, sizeof(size), &hash);
if (system_token) {

18
src/boot/efi/random-seed.h
View File

@ -2,21 +2,5 @@
#pragma once
#include <efi.h>
#include <errno.h>
#include <uchar.h>
typedef enum RandomSeedMode {
RANDOM_SEED_OFF,
RANDOM_SEED_WITH_SYSTEM_TOKEN,
RANDOM_SEED_ALWAYS,
_RANDOM_SEED_MODE_MAX,
_RANDOM_SEED_MODE_INVALID = -EINVAL,
} RandomSeedMode;
static const char16_t * const random_seed_modes_table[_RANDOM_SEED_MODE_MAX] = {
[RANDOM_SEED_OFF] = L"off",
[RANDOM_SEED_WITH_SYSTEM_TOKEN] = L"with-system-token",
[RANDOM_SEED_ALWAYS] = L"always",
};
EFI_STATUS process_random_seed(EFI_FILE *root_dir, RandomSeedMode mode);
EFI_STATUS process_random_seed(EFI_FILE *root_dir);

3
src/shared/bootspec.c
View File

@ -419,7 +419,6 @@ void boot_config_free(BootConfig *config) {
free(config->auto_entries);
free(config->auto_firmware);
free(config->console_mode);
free(config->random_seed_mode);
free(config->beep);
free(config->entry_oneshot);
@ -486,7 +485,7 @@ int boot_loader_read_conf(BootConfig *config, FILE *file, const char *path) {
else if (streq(field, "console-mode"))
r = free_and_strdup(&config->console_mode, p);
else if (streq(field, "random-seed-mode"))
r = free_and_strdup(&config->random_seed_mode, p);
log_syntax(NULL, LOG_WARNING, path, line, 0, "'random-seed-mode' has been deprecated, ignoring.");
else if (streq(field, "beep"))
r = free_and_strdup(&config->beep, p);
else {

1
src/shared/bootspec.h
View File

@ -57,7 +57,6 @@ typedef struct BootConfig {
char *auto_entries;
char *auto_firmware;
char *console_mode;
char *random_seed_mode;
char *beep;
char *entry_oneshot;