Add madvise12 test

Verify that MADV_GUARD_INSTALL is causing SIGSEGV when someone is
trying to access memory advised with it.

Closes: #1210
Reviewed-by: Petr Vorel <[email protected]>
Signed-off-by: Andrea Cervesato <[email protected]>

runtest/syscalls

@@ -1000,6 +1000,7 @@ madvise08 madvise08
 madvise09 madvise09
 madvise10 madvise10
 madvise11 madvise11
+madvise12 madvise12
 
 newuname01 newuname01
 

testcases/kernel/syscalls/madvise/.gitignore

@@ -8,3 +8,4 @@
 /madvise09
 /madvise10
 /madvise11
+/madvise12

testcases/kernel/syscalls/madvise/madvise12.c

@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (c) 2024 Andrea Cervesato <[email protected]>
+ */
+
+/*\
+ * [Description]
+ *
+ * Verify that MADV_GUARD_INSTALL is causing SIGSEGV when someone is accessing
+ * memory advised with it.
+ *
+ * This is a test for feature implemented in
+ * 662df3e5c376 ("mm: madvise: implement lightweight guard page mechanism")
+ *
+ * [Algorithm]
+ *
+ * - allocate a certain amount of memory
+ * - advise memory with MADV_GUARD_INSTALL
+ * - access to memory from within a child and verify it gets killed by SIGSEGV
+ * - release memory with MADV_GUARD_REMOVE
+ * - verify that memory has not been modified before child got killed
+ * - modify memory within a new child
+ * - verify that memory is accessable and child was not killed by SIGSEGV
+ */
+
+#include "tst_test.h"
+#include "lapi/mmap.h"
+
+#define MAP_SIZE (8 * TST_KB)
+
+static char *addr;
+
+static void run(void)
+{
+	pid_t pid;
+	int status;
+
+	memset(addr, 0, MAP_SIZE);
+
+	TST_EXP_PASS(madvise(addr, MAP_SIZE, MADV_GUARD_INSTALL));
+
+	pid = SAFE_FORK();
+	if (!pid) {
+		tst_res(TINFO, "Modifying memory content");
+
+		memset(addr, 'a', MAP_SIZE);
+		exit(0);
+	}
+
+	SAFE_WAITPID(pid, &status, 0);
+
+	if (WIFSIGNALED(status) && WTERMSIG(status) == SIGSEGV)
+		tst_res(TPASS, "Child ended by SIGSEGV as expected");
+	else
+		tst_res(TFAIL, "Child: %s", tst_strstatus(status));
+
+	TST_EXP_PASS(madvise(addr, MAP_SIZE, MADV_GUARD_REMOVE));
+
+	for (int i = 0; i < MAP_SIZE; i++) {
+		if (addr[i] == 'a') {
+			tst_res(TFAIL, "Memory content has been modified");
+			return;
+		}
+	}
+
+	tst_res(TPASS, "Memory content didn't change");
+
+	pid = SAFE_FORK();
+	if (!pid) {
+		tst_res(TINFO, "Modifying memory content");
+
+		memset(addr, 'b', MAP_SIZE);
+		exit(0);
+	}
+
+	SAFE_WAITPID(pid, &status, 0);
+
+	if (!WIFSIGNALED(status))
+		tst_res(TPASS, "Child ended without being signaled");
+	else
+		tst_res(TFAIL, "Child ended with %s", tst_strstatus(status));
+}
+
+static void setup(void)
+{
+	addr = SAFE_MMAP(NULL, MAP_SIZE,
+			PROT_READ | PROT_WRITE,
+			MAP_PRIVATE | MAP_ANONYMOUS,
+			-1, 0);
+}
+
+static void cleanup(void)
+{
+	if (addr)
+		SAFE_MUNMAP(addr, MAP_SIZE);
+}
+
+static struct tst_test test = {
+	.test_all = run,
+	.setup = setup,
+	.cleanup = cleanup,
+	.needs_root = 1,
+	.forks_child = 1,
+	.min_kver = "6.13",
+};