diff options
Diffstat (limited to 'drivers/hv/hv_common.c')
| -rw-r--r-- | drivers/hv/hv_common.c | 69 |
1 files changed, 69 insertions, 0 deletions
diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c index 5d64cb0a709d..dde3f9b6871a 100644 --- a/drivers/hv/hv_common.c +++ b/drivers/hv/hv_common.c @@ -20,8 +20,11 @@ #include <linux/sched/task_stack.h> #include <linux/panic_notifier.h> #include <linux/ptrace.h> +#include <linux/random.h> +#include <linux/efi.h> #include <linux/kdebug.h> #include <linux/kmsg_dump.h> +#include <linux/sizes.h> #include <linux/slab.h> #include <linux/dma-map-ops.h> #include <linux/set_memory.h> @@ -355,6 +358,72 @@ int __init hv_common_init(void) return 0; } +void __init ms_hyperv_late_init(void) +{ + struct acpi_table_header *header; + acpi_status status; + u8 *randomdata; + u32 length, i; + + /* + * Seed the Linux random number generator with entropy provided by + * the Hyper-V host in ACPI table OEM0. + */ + if (!IS_ENABLED(CONFIG_ACPI)) + return; + + status = acpi_get_table("OEM0", 0, &header); + if (ACPI_FAILURE(status) || !header) + return; + + /* + * Since the "OEM0" table name is for OEM specific usage, verify + * that what we're seeing purports to be from Microsoft. + */ + if (strncmp(header->oem_table_id, "MICROSFT", 8)) + goto error; + + /* + * Ensure the length is reasonable. Requiring at least 8 bytes and + * no more than 4K bytes is somewhat arbitrary and just protects + * against a malformed table. Hyper-V currently provides 64 bytes, + * but allow for a change in a later version. + */ + if (header->length < sizeof(*header) + 8 || + header->length > sizeof(*header) + SZ_4K) + goto error; + + length = header->length - sizeof(*header); + randomdata = (u8 *)(header + 1); + + pr_debug("Hyper-V: Seeding rng with %d random bytes from ACPI table OEM0\n", + length); + + add_bootloader_randomness(randomdata, length); + + /* + * To prevent the seed data from being visible in /sys/firmware/acpi, + * zero out the random data in the ACPI table and fixup the checksum. + * The zero'ing is done out of an abundance of caution in avoiding + * potential security risks to the rng. Similarly, reset the table + * length to just the header size so that a subsequent kexec doesn't + * try to use the zero'ed out random data. + */ + for (i = 0; i < length; i++) { + header->checksum += randomdata[i]; + randomdata[i] = 0; + } + + for (i = 0; i < sizeof(header->length); i++) + header->checksum += ((u8 *)&header->length)[i]; + header->length = sizeof(*header); + for (i = 0; i < sizeof(header->length); i++) + header->checksum -= ((u8 *)&header->length)[i]; + +error: + acpi_put_table(header); +} + /* * Hyper-V specific initialization and die code for * individual CPUs that is common across all architectures. |