From 19f4f86bfed21c5326ed2acebe1163f3a83e832b Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 04:25:50 +0200 Subject: Adding upstream version 241. Signed-off-by: Daniel Baumann --- src/basic/random-util.c | 265 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 265 insertions(+) create mode 100644 src/basic/random-util.c (limited to 'src/basic/random-util.c') diff --git a/src/basic/random-util.c b/src/basic/random-util.c new file mode 100644 index 0000000..f7decf6 --- /dev/null +++ b/src/basic/random-util.c @@ -0,0 +1,265 @@ +/* SPDX-License-Identifier: LGPL-2.1+ */ + +#if defined(__i386__) || defined(__x86_64__) +#include +#endif + +#include +#include +#include +#include +#include +#include +#include +#include + +#if HAVE_SYS_AUXV_H +# include +#endif + +#if USE_SYS_RANDOM_H +# include +#else +# include +#endif + +#include "fd-util.h" +#include "io-util.h" +#include "missing.h" +#include "random-util.h" +#include "time-util.h" + +#if HAS_FEATURE_MEMORY_SANITIZER +#include +#endif + +int rdrand(unsigned long *ret) { + +#if defined(__i386__) || defined(__x86_64__) + static int have_rdrand = -1; + unsigned char err; + + if (have_rdrand < 0) { + uint32_t eax, ebx, ecx, edx; + + /* Check if RDRAND is supported by the CPU */ + if (__get_cpuid(1, &eax, &ebx, &ecx, &edx) == 0) { + have_rdrand = false; + return -EOPNOTSUPP; + } + + have_rdrand = !!(ecx & (1U << 30)); + } + + if (have_rdrand == 0) + return -EOPNOTSUPP; + + asm volatile("rdrand %0;" + "setc %1" + : "=r" (*ret), + "=qm" (err)); + +#if HAS_FEATURE_MEMORY_SANITIZER + __msan_unpoison(&err, sizeof(err)); +#endif + + if (!err) + return -EAGAIN; + + return 0; +#else + return -EOPNOTSUPP; +#endif +} + +int genuine_random_bytes(void *p, size_t n, RandomFlags flags) { + static int have_syscall = -1; + _cleanup_close_ int fd = -1; + bool got_some = false; + int r; + + /* Gathers some randomness from the kernel (or the CPU if the RANDOM_ALLOW_RDRAND flag is set). This call won't + * block, unless the RANDOM_BLOCK flag is set. If RANDOM_DONT_DRAIN is set, an error is returned if the random + * pool is not initialized. Otherwise it will always return some data from the kernel, regardless of whether + * the random pool is fully initialized or not. */ + + if (n == 0) + return 0; + + if (FLAGS_SET(flags, RANDOM_ALLOW_RDRAND)) + /* Try x86-64' RDRAND intrinsic if we have it. We only use it if high quality randomness is not + * required, as we don't trust it (who does?). Note that we only do a single iteration of RDRAND here, + * even though the Intel docs suggest calling this in a tight loop of 10 invocations or so. That's + * because we don't really care about the quality here. We generally prefer using RDRAND if the caller + * allows us too, since this way we won't drain the kernel randomness pool if we don't need it, as the + * pool's entropy is scarce. */ + for (;;) { + unsigned long u; + size_t m; + + if (rdrand(&u) < 0) { + if (got_some && FLAGS_SET(flags, RANDOM_EXTEND_WITH_PSEUDO)) { + /* Fill in the remaining bytes using pseudo-random values */ + pseudo_random_bytes(p, n); + return 0; + } + + /* OK, this didn't work, let's go to getrandom() + /dev/urandom instead */ + break; + } + + m = MIN(sizeof(u), n); + memcpy(p, &u, m); + + p = (uint8_t*) p + m; + n -= m; + + if (n == 0) + return 0; /* Yay, success! */ + + got_some = true; + } + + /* Use the getrandom() syscall unless we know we don't have it. */ + if (have_syscall != 0 && !HAS_FEATURE_MEMORY_SANITIZER) { + + for (;;) { + r = getrandom(p, n, FLAGS_SET(flags, RANDOM_BLOCK) ? 0 : GRND_NONBLOCK); + if (r > 0) { + have_syscall = true; + + if ((size_t) r == n) + return 0; /* Yay, success! */ + + assert((size_t) r < n); + p = (uint8_t*) p + r; + n -= r; + + if (FLAGS_SET(flags, RANDOM_EXTEND_WITH_PSEUDO)) { + /* Fill in the remaining bytes using pseudo-random values */ + pseudo_random_bytes(p, n); + return 0; + } + + got_some = true; + + /* Hmm, we didn't get enough good data but the caller insists on good data? Then try again */ + if (FLAGS_SET(flags, RANDOM_BLOCK)) + continue; + + /* Fill in the rest with /dev/urandom */ + break; + + } else if (r == 0) { + have_syscall = true; + return -EIO; + + } else if (errno == ENOSYS) { + /* We lack the syscall, continue with reading from /dev/urandom. */ + have_syscall = false; + break; + + } else if (errno == EAGAIN) { + /* The kernel has no entropy whatsoever. Let's remember to use the syscall the next + * time again though. + * + * If RANDOM_DONT_DRAIN is set, return an error so that random_bytes() can produce some + * pseudo-random bytes instead. Otherwise, fall back to /dev/urandom, which we know is empty, + * but the kernel will produce some bytes for us on a best-effort basis. */ + have_syscall = true; + + if (got_some && FLAGS_SET(flags, RANDOM_EXTEND_WITH_PSEUDO)) { + /* Fill in the remaining bytes using pseudorandom values */ + pseudo_random_bytes(p, n); + return 0; + } + + if (FLAGS_SET(flags, RANDOM_DONT_DRAIN)) + return -ENODATA; + + /* Use /dev/urandom instead */ + break; + } else + return -errno; + } + } + + fd = open("/dev/urandom", O_RDONLY|O_CLOEXEC|O_NOCTTY); + if (fd < 0) + return errno == ENOENT ? -ENOSYS : -errno; + + return loop_read_exact(fd, p, n, true); +} + +void initialize_srand(void) { + static bool srand_called = false; + unsigned x; +#if HAVE_SYS_AUXV_H + const void *auxv; +#endif + unsigned long k; + + if (srand_called) + return; + +#if HAVE_SYS_AUXV_H + /* The kernel provides us with 16 bytes of entropy in auxv, so let's + * try to make use of that to seed the pseudo-random generator. It's + * better than nothing... */ + + auxv = (const void*) getauxval(AT_RANDOM); + if (auxv) { + assert_cc(sizeof(x) <= 16); + memcpy(&x, auxv, sizeof(x)); + } else +#endif + x = 0; + + x ^= (unsigned) now(CLOCK_REALTIME); + x ^= (unsigned) gettid(); + + if (rdrand(&k) >= 0) + x ^= (unsigned) k; + + srand(x); + srand_called = true; +} + +/* INT_MAX gives us only 31 bits, so use 24 out of that. */ +#if RAND_MAX >= INT_MAX +# define RAND_STEP 3 +#else +/* SHORT_INT_MAX or lower gives at most 15 bits, we just just 8 out of that. */ +# define RAND_STEP 1 +#endif + +void pseudo_random_bytes(void *p, size_t n) { + uint8_t *q; + + initialize_srand(); + + for (q = p; q < (uint8_t*) p + n; q += RAND_STEP) { + unsigned rr; + + rr = (unsigned) rand(); + +#if RAND_STEP >= 3 + if ((size_t) (q - (uint8_t*) p + 2) < n) + q[2] = rr >> 16; +#endif +#if RAND_STEP >= 2 + if ((size_t) (q - (uint8_t*) p + 1) < n) + q[1] = rr >> 8; +#endif + q[0] = rr; + } +} + +void random_bytes(void *p, size_t n) { + + if (genuine_random_bytes(p, n, RANDOM_EXTEND_WITH_PSEUDO|RANDOM_DONT_DRAIN|RANDOM_ALLOW_RDRAND) >= 0) + return; + + /* If for some reason some user made /dev/urandom unavailable to us, or the kernel has no entropy, use a PRNG instead. */ + pseudo_random_bytes(p, n); +} -- cgit v1.2.3