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Message-ID: <20240905173220.2243959-1-Jason@zx2c4.com>
Date: Thu, 5 Sep 2024 19:31:39 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: linux-kernel@...r.kernel.org,
christophe.leroy@...roup.eu,
adhemerval.zanella@...aro.org,
xry111@...111.site
Cc: "Jason A. Donenfeld" <Jason@...c4.com>
Subject: [PATCH] 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 implies that the RNG appears initialized, 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 vgetrandom
doesn't get called. If it doesn't get called, then the test succeeds.
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
.../selftests/vDSO/vdso_test_getrandom.c | 41 ++++++++++++++++++-
1 file changed, 40 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/vDSO/vdso_test_getrandom.c b/tools/testing/selftests/vDSO/vdso_test_getrandom.c
index 8866b65a4605..dfda5061f454 100644
--- a/tools/testing/selftests/vDSO/vdso_test_getrandom.c
+++ b/tools/testing/selftests/vDSO/vdso_test_getrandom.c
@@ -16,8 +16,11 @@
#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/ptrace.h>
#include "../kselftest.h"
#include "parse_vdso.h"
@@ -239,9 +242,10 @@ 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 +254,41 @@ static void kselftest(void)
}
ksft_test_result_pass("getrandom: PASS\n");
+
+ assert(unshare(CLONE_NEWUSER) == 0 && 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.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);
}
--
2.46.0
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