Commit 2aec9003 authored by Jason A. Donenfeld's avatar Jason A. Donenfeld
Browse files

selftests: vDSO: ensure vgetrandom works in a time namespace 



After verifying that vDSO getrandom does work, which ensures that the
RNG is initialized, test to see if it also works inside of a time
namespace. This is important to test, because the vvar pages get
swizzled around there. If the arch code isn't careful, the RNG will
appear uninitialized inside of a time namespace.

Because broken code makes the RNG appear uninitialized, test that
everything works by issuing a call to vgetrandom from a fork in a time
namespace, and use ptrace to ensure that the actual syscall getrandom
doesn't get called. If it doesn't get called, then the test succeeds.

Signed-off-by: default avatarJason A. Donenfeld <Jason@zx2c4.com>
parent 33ffa2dd

tools/testing/selftests/vDSO/vdso_test_getrandom.c

+42 −1
Original line number Diff line number Diff line
@@ -16,8 +16,12 @@ 
#include <sys/mman.h>

#include <sys/random.h>

#include <sys/syscall.h>

#include <sys/ptrace.h>

#include <sys/wait.h>

#include <sys/types.h>

#include <linux/random.h>

#include <linux/compiler.h>

#include <linux/ptrace.h>



#include "../kselftest.h"

#include "parse_vdso.h"
@@ -239,9 +243,10 @@ static void fill(void) 
static void kselftest(void)

{

	uint8_t weird_size[1263];

	pid_t child;



	ksft_print_header();

	ksft_set_plan(1);

	ksft_set_plan(2);



	for (size_t i = 0; i < 1000; ++i) {

		ssize_t ret = vgetrandom(weird_size, sizeof(weird_size), 0);
@@ -250,6 +255,42 @@ static void kselftest(void) 
	}



	ksft_test_result_pass("getrandom: PASS\n");



	unshare(CLONE_NEWUSER);

	assert(unshare(CLONE_NEWTIME) == 0);

	child = fork();

	assert(child >= 0);

	if (!child) {

		vgetrandom_init();

		child = getpid();

		assert(ptrace(PTRACE_TRACEME, 0, NULL, NULL) == 0);

		assert(kill(child, SIGSTOP) == 0);

		assert(vgetrandom(weird_size, sizeof(weird_size), 0) == sizeof(weird_size));

		_exit(0);

	}

	for (;;) {

		struct ptrace_syscall_info info = { 0 };

		int status, ret;

		assert(waitpid(child, &status, 0) >= 0);

		if (WIFEXITED(status)) {

			if (WEXITSTATUS(status) != 0)

				exit(KSFT_FAIL);

			break;

		}

		assert(WIFSTOPPED(status));

		if (WSTOPSIG(status) == SIGSTOP)

			assert(ptrace(PTRACE_SETOPTIONS, child, 0, PTRACE_O_TRACESYSGOOD) == 0);

		else if (WSTOPSIG(status) == (SIGTRAP | 0x80)) {

			assert(ptrace(PTRACE_GET_SYSCALL_INFO, child, sizeof(info), &info) > 0);

			if (info.op == PTRACE_SYSCALL_INFO_ENTRY && info.entry.nr == __NR_getrandom &&

			    info.entry.args[0] == (uintptr_t)weird_size && info.entry.args[1] == sizeof(weird_size))

				exit(KSFT_FAIL);

		}

		assert(ptrace(PTRACE_SYSCALL, child, 0, 0) == 0);

	}



	ksft_test_result_pass("getrandom timens: PASS\n");



	exit(KSFT_PASS);

}