diff options
| -rw-r--r-- | src/basic/random-util.c | 15 |
1 files changed, 14 insertions, 1 deletions
diff --git a/src/basic/random-util.c b/src/basic/random-util.c index b8bbf2d418..0561f0cb22 100644 --- a/src/basic/random-util.c +++ b/src/basic/random-util.c @@ -35,6 +35,7 @@ int rdrand(unsigned long *ret) { #if defined(__i386__) || defined(__x86_64__) static int have_rdrand = -1; + unsigned long v; uint8_t success; if (have_rdrand < 0) { @@ -59,12 +60,24 @@ int rdrand(unsigned long *ret) { asm volatile("rdrand %0;" "setc %1" - : "=r" (*ret), + : "=r" (v), "=qm" (success)); msan_unpoison(&success, sizeof(success)); if (!success) return -EAGAIN; + /* Apparently on some AMD CPUs RDRAND will sometimes (after a suspend/resume cycle?) report success + * via the carry flag but nonetheless return the same fixed value -1 in all cases. This appears to be + * a bad bug in the CPU or firmware. Let's deal with that and work-around this by explicitly checking + * for this special value (and also 0, just to be sure) and filtering it out. This is a work-around + * only however and something AMD really should fix properly. The Linux kernel should probably work + * around this issue by turning off RDRAND altogether on those CPUs. See: + * https://github.com/systemd/systemd/issues/11810 */ + if (v == 0 || v == ULONG_MAX) + return log_debug_errno(SYNTHETIC_ERRNO(EUCLEAN), + "RDRAND returned suspicious value %lx, assuming bad hardware RNG, not using value.", v); + + *ret = v; return 0; #else return -EOPNOTSUPP; |