diff options
| author | Jason A. Donenfeld <Jason@zx2c4.com> | 2022-07-13 01:12:21 +0200 |
|---|---|---|
| committer | Jason A. Donenfeld <Jason@zx2c4.com> | 2022-07-18 15:04:04 +0200 |
| commit | 0b9ba6135d7f18b82f3d8bebb55ded725ba88e0e (patch) | |
| tree | 66de7e09bef6d6693e35e8f50446ae8e2ed01267 /arch/um/kernel | |
| parent | b7a68f67ff4911e8a842d03f6f97fa91a8d483f5 (diff) | |
um: seed rng using host OS rng
UML generally does not provide access to special CPU instructions like
RDRAND, and execution tends to be rather deterministic, with no real
hardware interrupts, making good randomness really very hard, if not
all together impossible. Not only is this a security eyebrow raiser, but
it's also quite annoying when trying to do various pieces of UML-based
automation that takes a long time to boot, if ever.
Fix this by trivially calling getrandom() in the host and using that
seed as "bootloader randomness", which initializes the rng immediately
at UML boot.
The old behavior can be restored the same way as on any other arch, by
way of CONFIG_TRUST_BOOTLOADER_RANDOMNESS=n or
random.trust_bootloader=0. So seen from that perspective, this just
makes UML act like other archs, which is positive in its own right.
Additionally, wire up arch_get_random_{int,long}() in the same way, so
that reseeds can also make use of the host RNG, controllable by
CONFIG_TRUST_CPU_RANDOMNESS and random.trust_cpu, per usual.
Cc: stable@vger.kernel.org
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Acked-By: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Diffstat (limited to 'arch/um/kernel')
| -rw-r--r-- | arch/um/kernel/um_arch.c | 8 |
1 files changed, 8 insertions, 0 deletions
diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c index 0760e24f2eba..74f3efd96bd4 100644 --- a/arch/um/kernel/um_arch.c +++ b/arch/um/kernel/um_arch.c @@ -16,6 +16,7 @@ #include <linux/sched/task.h> #include <linux/kmsg_dump.h> #include <linux/suspend.h> +#include <linux/random.h> #include <asm/processor.h> #include <asm/cpufeature.h> @@ -406,6 +407,8 @@ int __init __weak read_initrd(void) void __init setup_arch(char **cmdline_p) { + u8 rng_seed[32]; + stack_protections((unsigned long) &init_thread_info); setup_physmem(uml_physmem, uml_reserved, physmem_size, highmem); mem_total_pages(physmem_size, iomem_size, highmem); @@ -416,6 +419,11 @@ void __init setup_arch(char **cmdline_p) strlcpy(boot_command_line, command_line, COMMAND_LINE_SIZE); *cmdline_p = command_line; setup_hostinfo(host_info, sizeof host_info); + + if (os_getrandom(rng_seed, sizeof(rng_seed), 0) == sizeof(rng_seed)) { + add_bootloader_randomness(rng_seed, sizeof(rng_seed)); + memzero_explicit(rng_seed, sizeof(rng_seed)); + } } void __init check_bugs(void) |