[Devel] [PATCH hci-8.1 7/7] selftests/mm: check MADV_DOEXEC on /dev/zero and exec permission

[Konstantin Khorenko <khorenko@virtuozzo.com>]

Add two cases to doexec:

- A private /dev/zero mapping is marked and preserved across exec. The
  mapping is anonymous but holds a reference to the file; a copy that
  does not take its own shows up as an fput() underflow at teardown.
- A marked range cannot be made executable until MADV_DONTEXEC, and
  MADV_DONTEXEC does not make a /dev/zero mapping from a noexec tmpfs
  executable. The noexec part needs a private mount namespace, a tmpfs
  mount and a /dev/zero node on it; the case is reported as skipped
  when it cannot get them.

https://virtuozzo.atlassian.net/browse/VSTOR-150232

Feature: oracle/mm: MADV_DOEXEC madvise() flag
Assisted-by: LLM
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 tools/testing/selftests/mm/doexec.c | 94 ++++++++++++++++++++++++++++++++++++-
 1 file changed, 92 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/mm/doexec.c b/tools/testing/selftests/mm/doexec.c
index dfa3da2c43934..97e045ba678e8 100644
--- a/tools/testing/selftests/mm/doexec.c
+++ b/tools/testing/selftests/mm/doexec.c
@@ -17,10 +17,12 @@
 #include <string.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
+#include <sys/mount.h>
 #include <sys/resource.h>
 #include <sys/sendfile.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
+#include <sys/sysmacros.h>
 #include <sys/wait.h>
 #include <unistd.h>
 
@@ -501,6 +503,88 @@ static int setuid_exec(void)
 	return ret;
 }
 
+/* A private /dev/zero mapping is anonymous but holds a file reference. */
+static int devzero_exec(void)
+{
+	size_t size = 16 * sysconf(_SC_PAGESIZE);
+	int fd = open("/dev/zero", O_RDWR);
+	char *ram;
+
+	if (fd < 0)
+		return KSFT_SKIP;
+	ram = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	close(fd);
+	if (ram == MAP_FAILED)
+		return KSFT_FAIL;
+	memset(ram, 0x31, size);
+	if (madvise(ram, size, MADV_DOEXEC))
+		return errno == EINVAL ? KSFT_SKIP : KSFT_FAIL;
+	check_exec(ram, size, 1, false);
+	return KSFT_FAIL;
+}
+
+static bool exec_refused(char *ram, size_t size)
+{
+	return mprotect(ram, size, PROT_READ | PROT_EXEC) && errno == EACCES;
+}
+
+/* MADV_DONTEXEC must not grant more than mmap() did on a noexec mount. */
+static int noexec_dontexec(void)
+{
+	size_t size = sysconf(_SC_PAGESIZE);
+	char dir[] = "/tmp/doexec-noexec.XXXXXX", node[64];
+	int fd, ret = KSFT_FAIL;
+	char *ram;
+
+	if (unshare(CLONE_NEWNS) || mount(NULL, "/", NULL, MS_REC | MS_PRIVATE, NULL) ||
+	    !mkdtemp(dir))
+		return KSFT_SKIP;
+	if (mount("tmpfs", dir, "tmpfs", MS_NOEXEC, NULL)) {
+		rmdir(dir);
+		return KSFT_SKIP;
+	}
+	snprintf(node, sizeof(node), "%s/zero", dir);
+	fd = mknod(node, S_IFCHR | 0600, makedev(1, 5)) ? -1 : open(node, O_RDWR);
+	if (fd < 0) {
+		ret = KSFT_SKIP;
+		goto out;
+	}
+	ram = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	close(fd);
+	if (ram == MAP_FAILED || !exec_refused(ram, size)) {
+		ret = KSFT_SKIP;
+		goto out;
+	}
+	if (madvise(ram, size, MADV_DOEXEC)) {
+		ret = errno == EINVAL ? KSFT_SKIP : KSFT_FAIL;
+		goto out;
+	}
+	if (!madvise(ram, size, MADV_DONTEXEC) && exec_refused(ram, size))
+		ret = KSFT_PASS;
+out:
+	umount2(dir, MNT_DETACH);
+	rmdir(dir);
+	return ret;
+}
+
+/* A marked range cannot become executable until it is unmarked. */
+static int doexec_noexec(void)
+{
+	size_t size = sysconf(_SC_PAGESIZE);
+	char *ram = preserved_ram(size);
+	int ret;
+
+	if (!ram)
+		return errno == EINVAL ? KSFT_SKIP : KSFT_FAIL;
+	if (!exec_refused(ram, size) || madvise(ram, size, MADV_DONTEXEC) ||
+	    mprotect(ram, size, PROT_READ | PROT_EXEC))
+		return KSFT_FAIL;
+	ret = noexec_dontexec();
+	if (ret == KSFT_SKIP)
+		ksft_print_msg("noexec mount part skipped\n");
+	return ret;
+}
+
 static void *exec_thread(void *arg)
 {
 	check_exec(arg, sysconf(_SC_PAGESIZE), 1, false);
@@ -861,7 +945,7 @@ int main(int argc, char **argv)
 		return KSFT_PASS;
 	}
 	ksft_print_header();
-	ksft_set_plan(NR_TESTS + 9);
+	ksft_set_plan(NR_TESTS + 11);
 	for (kind = 0; kind < NR_TESTS; kind++) {
 		fflush(stdout);
 		pid = fork();
@@ -884,7 +968,7 @@ int main(int argc, char **argv)
 		ksft_test_result_skip("pre-existing COW: DOEXEC unavailable\n");
 	else
 		ksft_test_result(ret == KSFT_PASS, "pre-existing COW preserved\n");
-	for (kind = 0; kind < 8; kind++) {
+	for (kind = 0; kind < 10; kind++) {
 		static const char * const extra_names[] = {
 			"CLONE_VM: recoverable EBUSY and retry",
 			"own threads: preserving exec allowed",
@@ -894,6 +978,8 @@ int main(int argc, char **argv)
 			"proc readers: repeated preserving exec allowed",
 			"concurrent CLONE_VM: shared memory is not stolen",
 			"setuid exec: preserving exec refused",
+			"private /dev/zero mapping: preserved across exec",
+			"marked range: not executable until unmarked",
 		};
 
 		fflush(stdout);
@@ -915,6 +1001,10 @@ int main(int argc, char **argv)
 				_exit(clone_exec_race());
 			case 7:
 				_exit(setuid_exec());
+			case 8:
+				_exit(devzero_exec());
+			case 9:
+				_exit(doexec_noexec());
 			}
 		}
 		ret = pid < 0 ? KSFT_FAIL : wait_child(pid);

-- 
2.43.0

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