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selftests: vDSO: ensure vgetrandom works in a time namespace

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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: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2024-09-05 19:17:24 +02:00
parent 33ffa2dd0d
commit 2aec90036d
1 changed files with 42 additions and 1 deletions
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43
tools/testing/selftests/vDSO/vdso_test_getrandom.c
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@ -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);
}