crypto/fipsmodule/rand/urandom_test.cc - boringssl - Git at Google

 /* Copyright (c) 2019, Google Inc.
  *
  * Permission to use, copy, modify, and/or distribute this software for any
  * purpose with or without fee is hereby granted, provided that the above
  * copyright notice and this permission notice appear in all copies.
  *
  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

 #include <gtest/gtest.h>
 #include <stdlib.h>

 #include <openssl/rand.h>

 #include "internal.h"
 #include "getrandom_fillin.h"

 #if defined(OPENSSL_X86_64) && !defined(BORINGSSL_SHARED_LIBRARY) && \
     !defined(BORINGSSL_UNSAFE_DETERMINISTIC_MODE) && defined(USE_NR_getrandom)

 #include <linux/random.h>
 #include <sys/ptrace.h>
 #include <sys/syscall.h>
 #include <sys/user.h>

 #if !defined(PTRACE_O_EXITKILL)
 #define PTRACE_O_EXITKILL (1 << 20)
 #endif

 #if defined(OPENSSL_NO_ASM)
 static int have_rdrand() { return 0; }
 #endif

 // This test can be run with $OPENSSL_ia32cap=~0x4000000000000000 in order to
 // simulate the absence of RDRAND of machines that have it.

 // Event represents a system call from urandom.c that is observed by the ptrace
 // code in |GetTrace|.
 struct Event {
   enum class Syscall {
     kGetRandom,
     kOpen,
     kUrandomRead,
     kUrandomIoctl,
     kAbort,
   };

   explicit Event(Syscall syscall) : type(syscall) {}

   bool operator==(const Event &other) const {
     return type == other.type && length == other.length &&
            flags == other.flags &&
            ((filename == nullptr && other.filename == nullptr) ||
             strcmp(filename, other.filename) == 0);
   }

   static Event GetRandom(size_t length, unsigned flags) {
     Event e(Syscall::kGetRandom);
     e.length = length;
     e.flags = flags;
     return e;
   }

   static Event Open(const char *filename) {
     Event e(Syscall::kOpen);
     e.filename = filename;
     return e;
   }

   static Event UrandomRead(size_t length) {
     Event e(Syscall::kUrandomRead);
     e.length = length;
     return e;
   }

   static Event UrandomIoctl() {
     Event e(Syscall::kUrandomIoctl);
     return e;
   }

   static Event Abort() {
     Event e(Syscall::kAbort);
     return e;
   }

   std::string String() const {
     char buf[256];

     switch (type) {
       case Syscall::kGetRandom:
         snprintf(buf, sizeof(buf), "getrandom(_, %zu, %d)", length, flags);
         break;

       case Syscall::kOpen:
         snprintf(buf, sizeof(buf), "open(%s, _)", filename);
         break;

       case Syscall::kUrandomRead:
         snprintf(buf, sizeof(buf), "read(urandom_fd, _, %zu)", length);
         break;

       case Syscall::kUrandomIoctl:
         return "ioctl(urandom_fd, RNDGETENTCNT, _)";

       case Syscall::kAbort:
         return "abort()";
     }

     return std::string(buf);
   }

   const Syscall type;
   size_t length = 0;
   unsigned flags = 0;
   const char *filename = nullptr;
 };

 static std::string ToString(const std::vector<Event> &trace) {
   std::string ret;
   for (const auto &event : trace) {
     if (!ret.empty()) {
       ret += ", ";
     }
     ret += event.String();
   }
   return ret;
 }

 // The following are flags to tell |GetTrace| to inject faults, using ptrace,
 // into the entropy-related system calls.

 // getrandom gives |ENOSYS|.
 static const unsigned NO_GETRANDOM = 1;
 // opening /dev/urandom fails.
 static const unsigned NO_URANDOM = 2;
 // getrandom always returns |EAGAIN| if given |GRNG_NONBLOCK|.
 static const unsigned GETRANDOM_NOT_READY = 4;
 // The ioctl on urandom returns only 255 bits of entropy the first time that
 // it's called.
 static const unsigned URANDOM_NOT_READY = 8;
 // getrandom gives |EINVAL| unless |NO_GETRANDOM| is set.
 static const unsigned GETRANDOM_ERROR = 16;
 // Reading from /dev/urandom gives |EINVAL|.
 static const unsigned URANDOM_ERROR = 32;
 static const unsigned NEXT_FLAG = 64;

 // GetTrace runs |thunk| in a forked process and observes the resulting system
 // calls using ptrace. It simulates a variety of failures based on the contents
 // of |flags| and records the observed events by appending to |out_trace|.
 static void GetTrace(std::vector<Event> *out_trace, unsigned flags,
                      std::function<void()> thunk) {
   const int child_pid = fork();
   ASSERT_NE(-1, child_pid);

   if (child_pid == 0) {
     // Child process
     if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0) {
       perror("PTRACE_TRACEME");
       _exit(1);
     }
     raise(SIGSTOP);
     thunk();
     _exit(0);
   }

   // Parent process
   int status;
   ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
   ASSERT_TRUE(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);

   // Set options so that:
   //   a) the child process is killed once this process dies.
   //   b) System calls result in a WSTOPSIG value of (SIGTRAP | 0x80) rather
   //      than just SIGTRAP. (This doesn't matter here, but it's recommended
   //      practice so that it's distinct from the signal itself.)
   ASSERT_EQ(0, ptrace(PTRACE_SETOPTIONS, child_pid, nullptr,
                       PTRACE_O_EXITKILL | PTRACE_O_TRACESYSGOOD))
       << strerror(errno);

   // urandom_fd tracks the file descriptor number for /dev/urandom in the child
   // process, if it opens it.
   int urandom_fd = -1;

   for (;;) {
     // Advance the child to the next system call.
     ASSERT_EQ(0, ptrace(PTRACE_SYSCALL, child_pid, 0, 0));
     ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));

     // The child may have aborted rather than made a system call.
     if (WIFSTOPPED(status) && WSTOPSIG(status) == SIGABRT) {
       out_trace->push_back(Event::Abort());
       break;
     }

     // Otherwise the only valid ptrace event is a system call stop.
     ASSERT_TRUE(WIFSTOPPED(status) && WSTOPSIG(status) == (SIGTRAP | 0x80));

     struct user_regs_struct regs;
     ASSERT_EQ(0, ptrace(PTRACE_GETREGS, child_pid, nullptr, &regs));
     const auto syscall_number = regs.orig_rax;

     bool is_opening_urandom = false;
     bool is_urandom_ioctl = false;
     uintptr_t ioctl_output_addr = 0;
     // inject_error is zero to indicate that the system call should run
     // normally. Otherwise it's, e.g. -EINVAL, to indicate that the system call
     // should not run and that error should be injected on return.
     int inject_error = 0;

     switch (syscall_number) {
       case __NR_getrandom:
         if (flags & NO_GETRANDOM) {
           inject_error = -ENOSYS;
         } else if (flags & GETRANDOM_ERROR) {
           inject_error = -EINVAL;
         } else if (flags & GETRANDOM_NOT_READY) {
           if (regs.rdx & GRND_NONBLOCK) {
             inject_error = -EAGAIN;
           }
         }
         out_trace->push_back(
             Event::GetRandom(/*length=*/regs.rsi, /*flags=*/regs.rdx));
         break;

       case __NR_openat:
       case __NR_open: {
         // It's assumed that any arguments to open(2) are constants in read-only
         // memory and thus the pointer in the child's context will also be a
         // valid pointer in our address space.
         const char *filename = reinterpret_cast<const char *>(
             (syscall_number == __NR_openat) ? regs.rsi : regs.rdi);
         out_trace->push_back(Event::Open(filename));
         is_opening_urandom = strcmp(filename, "/dev/urandom") == 0;
         if (is_opening_urandom && (flags & NO_URANDOM)) {
           inject_error = -ENOENT;
         }
         break;
       }

       case __NR_read: {
         const int read_fd = regs.rdi;
         if (urandom_fd >= 0 && urandom_fd == read_fd) {
           out_trace->push_back(Event::UrandomRead(/*length=*/regs.rdx));
           if (flags & URANDOM_ERROR) {
             inject_error = -EINVAL;
           }
         }
         break;
       }

       case __NR_ioctl: {
         const int ioctl_fd = regs.rdi;
         if (urandom_fd >= 0 && ioctl_fd == urandom_fd &&
             regs.rsi == RNDGETENTCNT) {
           out_trace->push_back(Event::UrandomIoctl());
           is_urandom_ioctl = true;
           ioctl_output_addr = regs.rdx;
         }
       }
     }

     if (inject_error) {
       // Replace the system call number with -1 to cause the kernel to ignore
       // the call. The -ENOSYS will be replaced later with the value of
       // |inject_error|.
       regs.orig_rax = -1;
       ASSERT_EQ(0, ptrace(PTRACE_SETREGS, child_pid, nullptr, &regs));
     }

     ASSERT_EQ(0, ptrace(PTRACE_SYSCALL, child_pid, 0, 0));
     ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
     // If the system call was exit/exit_group, the process may be terminated
     // rather than have exited the system call.
     if (WIFEXITED(status)) {
       ASSERT_EQ(0, WEXITSTATUS(status));
       return;
     }

     // Otherwise the next state must be a system call exit stop. This is
     // indistinguishable from a system call entry, we just have to keep track
     // and know that these events happen in pairs.
     ASSERT_TRUE(WIFSTOPPED(status) && WSTOPSIG(status) == (SIGTRAP | 0x80));

     if (inject_error) {
       if (inject_error != -ENOSYS) {
         ASSERT_EQ(0, ptrace(PTRACE_GETREGS, child_pid, nullptr, &regs));
         regs.rax = inject_error;
         ASSERT_EQ(0, ptrace(PTRACE_SETREGS, child_pid, nullptr, &regs));
       }
     } else if (is_opening_urandom) {
       ASSERT_EQ(0, ptrace(PTRACE_GETREGS, child_pid, nullptr, &regs));
       urandom_fd = regs.rax;
     } else if (is_urandom_ioctl) {
       // The result is the number of bits of entropy that the kernel currently
       // believes that it has. urandom.c waits until 256 bits are ready.
       int result = 256;

       // If we are simulating urandom not being ready then we have the ioctl
       // indicate one too few bits of entropy the first time it's queried.
       if (flags & URANDOM_NOT_READY) {
         result--;
         flags &= ~URANDOM_NOT_READY;
       }

       // ptrace always works with ill-defined "words", which appear to be 64-bit
       // on x86-64. Since the ioctl result is a 32-bit int, do a
       // read-modify-write to inject the answer.
       const uintptr_t aligned_addr = ioctl_output_addr & ~7;
       const uintptr_t offset = ioctl_output_addr - aligned_addr;
       union {
         uint64_t word;
         uint8_t bytes[8];
       } u;
       u.word = ptrace(PTRACE_PEEKDATA, child_pid,
                       reinterpret_cast<void *>(aligned_addr), nullptr);
       memcpy(&u.bytes[offset], &result, sizeof(result));
       ASSERT_EQ(0, ptrace(PTRACE_POKEDATA, child_pid,
                           reinterpret_cast<void *>(aligned_addr),
                           reinterpret_cast<void *>(u.word)));
     }
   }
 }

 // TestFunction is the function that |GetTrace| is asked to trace.
 static void TestFunction() {
   uint8_t byte;
   RAND_bytes(&byte, sizeof(byte));
   RAND_bytes(&byte, sizeof(byte));
 }

 // TestFunctionPRNGModel is a model of how the urandom.c code will behave when
 // |TestFunction| is run. It should return the same trace of events that
 // |GetTrace| will observe the real code making.
 static std::vector<Event> TestFunctionPRNGModel(unsigned flags) {
 #if defined(BORINGSSL_FIPS)
   static const bool is_fips = true;
 #else
   static const bool is_fips = false;
 #endif

   std::vector<Event> ret;
   bool urandom_probed = false;
   bool getrandom_ready = false;

   // Probe for getrandom support
   ret.push_back(Event::GetRandom(1, GRND_NONBLOCK));
   std::function<void()> wait_for_entropy;
   std::function<bool(bool, size_t)> sysrand;

   if (flags & NO_GETRANDOM) {
     ret.push_back(Event::Open("/dev/urandom"));
     if (flags & NO_URANDOM) {
       ret.push_back(Event::Abort());
       return ret;
     }

     wait_for_entropy = [&ret, &urandom_probed, flags] {
       if (!is_fips || urandom_probed) {
         return;
       }

       // Probe urandom for entropy.
       ret.push_back(Event::UrandomIoctl());
       if (flags & URANDOM_NOT_READY) {
         // If the first attempt doesn't report enough entropy, probe
         // repeatedly until it does, which will happen with the second attempt.
         ret.push_back(Event::UrandomIoctl());
       }

       urandom_probed = true;
     };

     sysrand = [&ret, &wait_for_entropy, flags](bool block, size_t len) {
       if (block) {
         wait_for_entropy();
       }
       ret.push_back(Event::UrandomRead(len));
       if (flags & URANDOM_ERROR) {
         ret.push_back(Event::Abort());
         return false;
       }
       return true;
     };
   } else {
     if (flags & GETRANDOM_ERROR) {
       ret.push_back(Event::Abort());
       return ret;
     }

     getrandom_ready = (flags & GETRANDOM_NOT_READY) == 0;
     wait_for_entropy = [&ret, &getrandom_ready] {
       if (getrandom_ready) {
         return;
       }

       ret.push_back(Event::GetRandom(1, GRND_NONBLOCK));
       ret.push_back(Event::GetRandom(1, 0));
       getrandom_ready = true;
     };
     sysrand = [&ret, &wait_for_entropy](bool block, size_t len) {
       if (block) {
         wait_for_entropy();
       }
       ret.push_back(Event::GetRandom(len, block ? 0 : GRND_NONBLOCK));
       return true;
     };
   }

   const size_t kSeedLength = CTR_DRBG_ENTROPY_LEN * (is_fips ? 10 : 1);
   const size_t kAdditionalDataLength = 32;

   if (!have_rdrand()) {
     if (!sysrand(true, kAdditionalDataLength) ||
         // Initialise CRNGT.
         (is_fips && !sysrand(true, 16)) ||
         !sysrand(true, kSeedLength) ||
         // Second entropy draw.
         !sysrand(true, kAdditionalDataLength)) {
       return ret;
     }
   } else {
     // Opportuntistic entropy draw in FIPS mode because RDRAND was used.
     // In non-FIPS mode it's just drawn from |CRYPTO_sysrand| in a blocking
     // way.
     if (!sysrand(!is_fips, CTR_DRBG_ENTROPY_LEN)) {
       return ret;
     }
   }

   return ret;
 }

 // Tests that |TestFunctionPRNGModel| is a correct model for the code in
 // urandom.c, at least to the limits of the the |Event| type.
 TEST(URandomTest, Test) {
   char buf[256];

 #define TRACE_FLAG(flag)                                         \
   snprintf(buf, sizeof(buf), #flag ": %d", (flags & flag) != 0); \
   SCOPED_TRACE(buf);

   for (unsigned flags = 0; flags < NEXT_FLAG; flags++) {
     TRACE_FLAG(NO_GETRANDOM);
     TRACE_FLAG(NO_URANDOM);
     TRACE_FLAG(GETRANDOM_NOT_READY);
     TRACE_FLAG(URANDOM_NOT_READY);
     TRACE_FLAG(GETRANDOM_ERROR);
     TRACE_FLAG(URANDOM_ERROR);

     const std::vector<Event> expected_trace = TestFunctionPRNGModel(flags);
     std::vector<Event> actual_trace;
     GetTrace(&actual_trace, flags, TestFunction);

     if (expected_trace != actual_trace) {
       ADD_FAILURE() << "Expected: " << ToString(expected_trace)
                     << "\nFound:    " << ToString(actual_trace);
     }
   }
 }

 int main(int argc, char **argv) {
   ::testing::InitGoogleTest(&argc, argv);
   return RUN_ALL_TESTS();
 }

 #else

 int main(int argc, char **argv) {
   printf("PASS\n");
   return 0;
 }

 #endif  // X86_64 && !SHARED_LIBRARY && !UNSAFE_DETERMINISTIC_MODE &&
         // USE_NR_getrandom
	/* Copyright (c) 2019, Google Inc.
	*
	* Permission to use, copy, modify, and/or distribute this software for any
	* purpose with or without fee is hereby granted, provided that the above
	* copyright notice and this permission notice appear in all copies.
	*
	* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
	* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
	* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
	* SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
	* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
	* OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
	* CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. */

	#include <gtest/gtest.h>
	#include <stdlib.h>

	#include <openssl/rand.h>

	#include "internal.h"
	#include "getrandom_fillin.h"

	#if defined(OPENSSL_X86_64) && !defined(BORINGSSL_SHARED_LIBRARY) && \
	!defined(BORINGSSL_UNSAFE_DETERMINISTIC_MODE) && defined(USE_NR_getrandom)

	#include <linux/random.h>
	#include <sys/ptrace.h>
	#include <sys/syscall.h>
	#include <sys/user.h>

	#if !defined(PTRACE_O_EXITKILL)
	#define PTRACE_O_EXITKILL (1 << 20)
	#endif

	#if defined(OPENSSL_NO_ASM)
	static int have_rdrand() { return 0; }
	#endif

	// This test can be run with $OPENSSL_ia32cap=~0x4000000000000000 in order to
	// simulate the absence of RDRAND of machines that have it.

	// Event represents a system call from urandom.c that is observed by the ptrace
	// code in \|GetTrace\|.
	struct Event {
	enum class Syscall {
	kGetRandom,
	kOpen,
	kUrandomRead,
	kUrandomIoctl,
	kAbort,
	};

	explicit Event(Syscall syscall) : type(syscall) {}

	bool operator==(const Event &other) const {
	return type == other.type && length == other.length &&
	flags == other.flags &&
	((filename == nullptr && other.filename == nullptr) \|\|
	strcmp(filename, other.filename) == 0);
	}

	static Event GetRandom(size_t length, unsigned flags) {
	Event e(Syscall::kGetRandom);
	e.length = length;
	e.flags = flags;
	return e;
	}

	static Event Open(const char *filename) {
	Event e(Syscall::kOpen);
	e.filename = filename;
	return e;
	}

	static Event UrandomRead(size_t length) {
	Event e(Syscall::kUrandomRead);
	e.length = length;
	return e;
	}

	static Event UrandomIoctl() {
	Event e(Syscall::kUrandomIoctl);
	return e;
	}

	static Event Abort() {
	Event e(Syscall::kAbort);
	return e;
	}

	std::string String() const {
	char buf[256];

	switch (type) {
	case Syscall::kGetRandom:
	snprintf(buf, sizeof(buf), "getrandom(_, %zu, %d)", length, flags);
	break;

	case Syscall::kOpen:
	snprintf(buf, sizeof(buf), "open(%s, _)", filename);
	break;

	case Syscall::kUrandomRead:
	snprintf(buf, sizeof(buf), "read(urandom_fd, _, %zu)", length);
	break;

	case Syscall::kUrandomIoctl:
	return "ioctl(urandom_fd, RNDGETENTCNT, _)";

	case Syscall::kAbort:
	return "abort()";
	}

	return std::string(buf);
	}

	const Syscall type;
	size_t length = 0;
	unsigned flags = 0;
	const char *filename = nullptr;
	};

	static std::string ToString(const std::vector<Event> &trace) {
	std::string ret;
	for (const auto &event : trace) {
	if (!ret.empty()) {
	ret += ", ";
	}
	ret += event.String();
	}
	return ret;
	}

	// The following are flags to tell \|GetTrace\| to inject faults, using ptrace,
	// into the entropy-related system calls.

	// getrandom gives \|ENOSYS\|.
	static const unsigned NO_GETRANDOM = 1;
	// opening /dev/urandom fails.
	static const unsigned NO_URANDOM = 2;
	// getrandom always returns \|EAGAIN\| if given \|GRNG_NONBLOCK\|.
	static const unsigned GETRANDOM_NOT_READY = 4;
	// The ioctl on urandom returns only 255 bits of entropy the first time that
	// it's called.
	static const unsigned URANDOM_NOT_READY = 8;
	// getrandom gives \|EINVAL\| unless \|NO_GETRANDOM\| is set.
	static const unsigned GETRANDOM_ERROR = 16;
	// Reading from /dev/urandom gives \|EINVAL\|.
	static const unsigned URANDOM_ERROR = 32;
	static const unsigned NEXT_FLAG = 64;

	// GetTrace runs \|thunk\| in a forked process and observes the resulting system
	// calls using ptrace. It simulates a variety of failures based on the contents
	// of \|flags\| and records the observed events by appending to \|out_trace\|.
	static void GetTrace(std::vector<Event> *out_trace, unsigned flags,
	std::function<void()> thunk) {
	const int child_pid = fork();
	ASSERT_NE(-1, child_pid);

	if (child_pid == 0) {
	// Child process
	if (ptrace(PTRACE_TRACEME, 0, 0, 0) != 0) {
	perror("PTRACE_TRACEME");
	_exit(1);
	}
	raise(SIGSTOP);
	thunk();
	_exit(0);
	}

	// Parent process
	int status;
	ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
	ASSERT_TRUE(WIFSTOPPED(status) && WSTOPSIG(status) == SIGSTOP);

	// Set options so that:
	// a) the child process is killed once this process dies.
	// b) System calls result in a WSTOPSIG value of (SIGTRAP \| 0x80) rather
	// than just SIGTRAP. (This doesn't matter here, but it's recommended
	// practice so that it's distinct from the signal itself.)
	ASSERT_EQ(0, ptrace(PTRACE_SETOPTIONS, child_pid, nullptr,
	PTRACE_O_EXITKILL \| PTRACE_O_TRACESYSGOOD))
	<< strerror(errno);

	// urandom_fd tracks the file descriptor number for /dev/urandom in the child
	// process, if it opens it.
	int urandom_fd = -1;

	for (;;) {
	// Advance the child to the next system call.
	ASSERT_EQ(0, ptrace(PTRACE_SYSCALL, child_pid, 0, 0));
	ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));

	// The child may have aborted rather than made a system call.
	if (WIFSTOPPED(status) && WSTOPSIG(status) == SIGABRT) {
	out_trace->push_back(Event::Abort());
	break;
	}

	// Otherwise the only valid ptrace event is a system call stop.
	ASSERT_TRUE(WIFSTOPPED(status) && WSTOPSIG(status) == (SIGTRAP \| 0x80));

	struct user_regs_struct regs;
	ASSERT_EQ(0, ptrace(PTRACE_GETREGS, child_pid, nullptr, &regs));
	const auto syscall_number = regs.orig_rax;

	bool is_opening_urandom = false;
	bool is_urandom_ioctl = false;
	uintptr_t ioctl_output_addr = 0;
	// inject_error is zero to indicate that the system call should run
	// normally. Otherwise it's, e.g. -EINVAL, to indicate that the system call
	// should not run and that error should be injected on return.
	int inject_error = 0;

	switch (syscall_number) {
	case __NR_getrandom:
	if (flags & NO_GETRANDOM) {
	inject_error = -ENOSYS;
	} else if (flags & GETRANDOM_ERROR) {
	inject_error = -EINVAL;
	} else if (flags & GETRANDOM_NOT_READY) {
	if (regs.rdx & GRND_NONBLOCK) {
	inject_error = -EAGAIN;
	}
	}
	out_trace->push_back(
	Event::GetRandom(/length=/regs.rsi, /flags=/regs.rdx));
	break;

	case __NR_openat:
	case __NR_open: {
	// It's assumed that any arguments to open(2) are constants in read-only
	// memory and thus the pointer in the child's context will also be a
	// valid pointer in our address space.
	const char filename = reinterpret_cast<const char >(
	(syscall_number == __NR_openat) ? regs.rsi : regs.rdi);
	out_trace->push_back(Event::Open(filename));
	is_opening_urandom = strcmp(filename, "/dev/urandom") == 0;
	if (is_opening_urandom && (flags & NO_URANDOM)) {
	inject_error = -ENOENT;
	}
	break;
	}

	case __NR_read: {
	const int read_fd = regs.rdi;
	if (urandom_fd >= 0 && urandom_fd == read_fd) {
	out_trace->push_back(Event::UrandomRead(/length=/regs.rdx));
	if (flags & URANDOM_ERROR) {
	inject_error = -EINVAL;
	}
	}
	break;
	}

	case __NR_ioctl: {
	const int ioctl_fd = regs.rdi;
	if (urandom_fd >= 0 && ioctl_fd == urandom_fd &&
	regs.rsi == RNDGETENTCNT) {
	out_trace->push_back(Event::UrandomIoctl());
	is_urandom_ioctl = true;
	ioctl_output_addr = regs.rdx;
	}
	}
	}

	if (inject_error) {
	// Replace the system call number with -1 to cause the kernel to ignore
	// the call. The -ENOSYS will be replaced later with the value of
	// \|inject_error\|.
	regs.orig_rax = -1;
	ASSERT_EQ(0, ptrace(PTRACE_SETREGS, child_pid, nullptr, &regs));
	}

	ASSERT_EQ(0, ptrace(PTRACE_SYSCALL, child_pid, 0, 0));
	ASSERT_EQ(child_pid, waitpid(child_pid, &status, 0));
	// If the system call was exit/exit_group, the process may be terminated
	// rather than have exited the system call.
	if (WIFEXITED(status)) {
	ASSERT_EQ(0, WEXITSTATUS(status));
	return;
	}

	// Otherwise the next state must be a system call exit stop. This is
	// indistinguishable from a system call entry, we just have to keep track
	// and know that these events happen in pairs.
	ASSERT_TRUE(WIFSTOPPED(status) && WSTOPSIG(status) == (SIGTRAP \| 0x80));

	if (inject_error) {
	if (inject_error != -ENOSYS) {
	ASSERT_EQ(0, ptrace(PTRACE_GETREGS, child_pid, nullptr, &regs));
	regs.rax = inject_error;
	ASSERT_EQ(0, ptrace(PTRACE_SETREGS, child_pid, nullptr, &regs));
	}
	} else if (is_opening_urandom) {
	ASSERT_EQ(0, ptrace(PTRACE_GETREGS, child_pid, nullptr, &regs));
	urandom_fd = regs.rax;
	} else if (is_urandom_ioctl) {
	// The result is the number of bits of entropy that the kernel currently
	// believes that it has. urandom.c waits until 256 bits are ready.
	int result = 256;

	// If we are simulating urandom not being ready then we have the ioctl
	// indicate one too few bits of entropy the first time it's queried.
	if (flags & URANDOM_NOT_READY) {
	result--;
	flags &= ~URANDOM_NOT_READY;
	}

	// ptrace always works with ill-defined "words", which appear to be 64-bit
	// on x86-64. Since the ioctl result is a 32-bit int, do a
	// read-modify-write to inject the answer.
	const uintptr_t aligned_addr = ioctl_output_addr & ~7;
	const uintptr_t offset = ioctl_output_addr - aligned_addr;
	union {
	uint64_t word;
	uint8_t bytes[8];
	} u;
	u.word = ptrace(PTRACE_PEEKDATA, child_pid,
	reinterpret_cast<void *>(aligned_addr), nullptr);
	memcpy(&u.bytes[offset], &result, sizeof(result));
	ASSERT_EQ(0, ptrace(PTRACE_POKEDATA, child_pid,
	reinterpret_cast<void *>(aligned_addr),
	reinterpret_cast<void *>(u.word)));
	}
	}
	}

	// TestFunction is the function that \|GetTrace\| is asked to trace.
	static void TestFunction() {
	uint8_t byte;
	RAND_bytes(&byte, sizeof(byte));
	RAND_bytes(&byte, sizeof(byte));
	}

	// TestFunctionPRNGModel is a model of how the urandom.c code will behave when
	// \|TestFunction\| is run. It should return the same trace of events that
	// \|GetTrace\| will observe the real code making.
	static std::vector<Event> TestFunctionPRNGModel(unsigned flags) {
	#if defined(BORINGSSL_FIPS)
	static const bool is_fips = true;
	#else
	static const bool is_fips = false;
	#endif

	std::vector<Event> ret;
	bool urandom_probed = false;
	bool getrandom_ready = false;

	// Probe for getrandom support
	ret.push_back(Event::GetRandom(1, GRND_NONBLOCK));
	std::function<void()> wait_for_entropy;
	std::function<bool(bool, size_t)> sysrand;

	if (flags & NO_GETRANDOM) {
	ret.push_back(Event::Open("/dev/urandom"));
	if (flags & NO_URANDOM) {
	ret.push_back(Event::Abort());
	return ret;
	}

	wait_for_entropy = [&ret, &urandom_probed, flags] {
	if (!is_fips \|\| urandom_probed) {
	return;
	}

	// Probe urandom for entropy.
	ret.push_back(Event::UrandomIoctl());
	if (flags & URANDOM_NOT_READY) {
	// If the first attempt doesn't report enough entropy, probe
	// repeatedly until it does, which will happen with the second attempt.
	ret.push_back(Event::UrandomIoctl());
	}

	urandom_probed = true;
	};

	sysrand = [&ret, &wait_for_entropy, flags](bool block, size_t len) {
	if (block) {
	wait_for_entropy();
	}
	ret.push_back(Event::UrandomRead(len));
	if (flags & URANDOM_ERROR) {
	ret.push_back(Event::Abort());
	return false;
	}
	return true;
	};
	} else {
	if (flags & GETRANDOM_ERROR) {
	ret.push_back(Event::Abort());
	return ret;
	}

	getrandom_ready = (flags & GETRANDOM_NOT_READY) == 0;
	wait_for_entropy = [&ret, &getrandom_ready] {
	if (getrandom_ready) {
	return;
	}

	ret.push_back(Event::GetRandom(1, GRND_NONBLOCK));
	ret.push_back(Event::GetRandom(1, 0));
	getrandom_ready = true;
	};
	sysrand = [&ret, &wait_for_entropy](bool block, size_t len) {
	if (block) {
	wait_for_entropy();
	}
	ret.push_back(Event::GetRandom(len, block ? 0 : GRND_NONBLOCK));
	return true;
	};
	}

	const size_t kSeedLength = CTR_DRBG_ENTROPY_LEN * (is_fips ? 10 : 1);
	const size_t kAdditionalDataLength = 32;

	if (!have_rdrand()) {
	if (!sysrand(true, kAdditionalDataLength) \|\|
	// Initialise CRNGT.
	(is_fips && !sysrand(true, 16)) \|\|
	!sysrand(true, kSeedLength) \|\|
	// Second entropy draw.
	!sysrand(true, kAdditionalDataLength)) {
	return ret;
	}
	} else {
	// Opportuntistic entropy draw in FIPS mode because RDRAND was used.
	// In non-FIPS mode it's just drawn from \|CRYPTO_sysrand\| in a blocking
	// way.
	if (!sysrand(!is_fips, CTR_DRBG_ENTROPY_LEN)) {
	return ret;
	}
	}

	return ret;
	}

	// Tests that \|TestFunctionPRNGModel\| is a correct model for the code in
	// urandom.c, at least to the limits of the the \|Event\| type.
	TEST(URandomTest, Test) {
	char buf[256];

	#define TRACE_FLAG(flag) \
	snprintf(buf, sizeof(buf), #flag ": %d", (flags & flag) != 0); \
	SCOPED_TRACE(buf);

	for (unsigned flags = 0; flags < NEXT_FLAG; flags++) {
	TRACE_FLAG(NO_GETRANDOM);
	TRACE_FLAG(NO_URANDOM);
	TRACE_FLAG(GETRANDOM_NOT_READY);
	TRACE_FLAG(URANDOM_NOT_READY);
	TRACE_FLAG(GETRANDOM_ERROR);
	TRACE_FLAG(URANDOM_ERROR);

	const std::vector<Event> expected_trace = TestFunctionPRNGModel(flags);
	std::vector<Event> actual_trace;
	GetTrace(&actual_trace, flags, TestFunction);

	if (expected_trace != actual_trace) {
	ADD_FAILURE() << "Expected: " << ToString(expected_trace)
	<< "\nFound: " << ToString(actual_trace);
	}
	}
	}

	int main(int argc, char **argv) {
	::testing::InitGoogleTest(&argc, argv);
	return RUN_ALL_TESTS();
	}

	#else

	int main(int argc, char **argv) {
	printf("PASS\n");
	return 0;
	}

	#endif // X86_64 && !SHARED_LIBRARY && !UNSAFE_DETERMINISTIC_MODE &&
	// USE_NR_getrandom