lkdtm: Add CONFIG hints in errors where possible

For various failure conditions, try to include some details about where
to look for reasons about the failure.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20210623203936.3151093-8-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/lkdtm/bugs.c

@@ -303,8 +303,10 @@ void lkdtm_CORRUPT_LIST_ADD(void)
 
 	if (target[0] == NULL && target[1] == NULL)
 		pr_err("Overwrite did not happen, but no BUG?!\n");
-	else
+	else {
 		pr_err("list_add() corruption not detected!\n");
+		pr_expected_config(CONFIG_DEBUG_LIST);
+	}
 }
 
 void lkdtm_CORRUPT_LIST_DEL(void)
@@ -328,8 +330,10 @@ void lkdtm_CORRUPT_LIST_DEL(void)
 
 	if (target[0] == NULL && target[1] == NULL)
 		pr_err("Overwrite did not happen, but no BUG?!\n");
-	else
+	else {
 		pr_err("list_del() corruption not detected!\n");
+		pr_expected_config(CONFIG_DEBUG_LIST);
+	}
 }
 
 /* Test that VMAP_STACK is actually allocating with a leading guard page */

drivers/misc/lkdtm/cfi.c

@@ -38,5 +38,6 @@ void lkdtm_CFI_FORWARD_PROTO(void)
 	func = (void *)lkdtm_increment_int;
 	func(&called_count);
 
-	pr_info("Fail: survived mismatched prototype function call!\n");
+	pr_err("FAIL: survived mismatched prototype function call!\n");
+	pr_expected_config(CONFIG_CFI_CLANG);
 }

drivers/misc/lkdtm/core.c

@@ -26,6 +26,7 @@
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/debugfs.h>
+#include <linux/init.h>
 
 #define DEFAULT_COUNT 10
 
@@ -398,6 +399,56 @@ static ssize_t direct_entry(struct file *f, const char __user *user_buf,
 	return count;
 }
 
+#ifndef MODULE
+/*
+ * To avoid needing to export parse_args(), just don't use this code
+ * when LKDTM is built as a module.
+ */
+struct check_cmdline_args {
+	const char *param;
+	int value;
+};
+
+static int lkdtm_parse_one(char *param, char *val,
+			   const char *unused, void *arg)
+{
+	struct check_cmdline_args *args = arg;
+
+	/* short circuit if we already found a value. */
+	if (args->value != -ESRCH)
+		return 0;
+	if (strncmp(param, args->param, strlen(args->param)) == 0) {
+		bool bool_result;
+		int ret;
+
+		ret = kstrtobool(val, &bool_result);
+		if (ret == 0)
+			args->value = bool_result;
+	}
+	return 0;
+}
+
+int lkdtm_check_bool_cmdline(const char *param)
+{
+	char *command_line;
+	struct check_cmdline_args args = {
+		.param = param,
+		.value = -ESRCH,
+	};
+
+	command_line = kstrdup(saved_command_line, GFP_KERNEL);
+	if (!command_line)
+		return -ENOMEM;
+
+	parse_args("Setting sysctl args", command_line,
+		   NULL, 0, -1, -1, &args, lkdtm_parse_one);
+
+	kfree(command_line);
+
+	return args.value;
+}
+#endif
+
 static struct dentry *lkdtm_debugfs_root;
 
 static int __init lkdtm_module_init(void)

drivers/misc/lkdtm/fortify.c

@@ -76,7 +76,8 @@ void lkdtm_FORTIFIED_STRSCPY(void)
 	 */
 	strscpy(dst, src, strlen(src));
 
-	pr_warn("FAIL: No overflow in above strscpy()\n");
+	pr_err("FAIL: strscpy() overflow not detected!\n");
+	pr_expected_config(CONFIG_FORTIFY_SOURCE);
 
 	kfree(src);
 }

drivers/misc/lkdtm/heap.c

@@ -109,9 +109,10 @@ void lkdtm_READ_AFTER_FREE(void)
 	if (saw != *val) {
 		/* Good! Poisoning happened, so declare a win. */
 		pr_info("Memory correctly poisoned (%x)\n", saw);
-		BUG();
+	} else {
+		pr_err("FAIL: Memory was not poisoned!\n");
+		pr_expected_config_param(CONFIG_INIT_ON_FREE_DEFAULT_ON, "init_on_free");
 	}
-	pr_info("Memory was not poisoned\n");
 
 	kfree(val);
 }
@@ -165,9 +166,10 @@ void lkdtm_READ_BUDDY_AFTER_FREE(void)
 	if (saw != *val) {
 		/* Good! Poisoning happened, so declare a win. */
 		pr_info("Memory correctly poisoned (%x)\n", saw);
-		BUG();
+	} else {
+		pr_err("FAIL: Buddy page was not poisoned!\n");
+		pr_expected_config_param(CONFIG_INIT_ON_FREE_DEFAULT_ON, "init_on_free");
 	}
-	pr_info("Buddy page was not poisoned\n");
 
 	kfree(val);
 }

drivers/misc/lkdtm/lkdtm.h

@@ -6,6 +6,47 @@
 
 #include <linux/kernel.h>
 
+#define pr_expected_config(kconfig)				\
+{								\
+	if (IS_ENABLED(kconfig)) 				\
+		pr_err("Unexpected! This kernel was built with " #kconfig "=y\n"); \
+	else							\
+		pr_warn("This is probably expected, since this kernel was built *without* " #kconfig "=y\n"); \
+}
+
+#ifndef MODULE
+int lkdtm_check_bool_cmdline(const char *param);
+#define pr_expected_config_param(kconfig, param)		\
+{								\
+	if (IS_ENABLED(kconfig)) {				\
+		switch (lkdtm_check_bool_cmdline(param)) {	\
+		case 0:						\
+			pr_warn("This is probably expected, since this kernel was built with " #kconfig "=y but booted with '" param "=N'\n"); \
+			break;					\
+		case 1:						\
+			pr_err("Unexpected! This kernel was built with " #kconfig "=y and booted with '" param "=Y'\n"); \
+			break;					\
+		default:					\
+			pr_err("Unexpected! This kernel was built with " #kconfig "=y (and booted without '" param "' specified)\n"); \
+		}						\
+	} else {						\
+		switch (lkdtm_check_bool_cmdline(param)) {	\
+		case 0:						\
+			pr_warn("This is probably expected, as kernel was built *without* " #kconfig "=y and booted with '" param "=N'\n"); \
+			break;					\
+		case 1:						\
+			pr_err("Unexpected! This kernel was built *without* " #kconfig "=y but booted with '" param "=Y'\n"); \
+			break;					\
+		default:					\
+			pr_err("This is probably expected, since this kernel was built *without* " #kconfig "=y (and booted without '" param "' specified)\n"); \
+			break;					\
+		}						\
+	}							\
+}
+#else
+#define pr_expected_config_param(kconfig, param) pr_expected_config(kconfig)
+#endif
+
 /* bugs.c */
 void __init lkdtm_bugs_init(int *recur_param);
 void lkdtm_PANIC(void);

drivers/misc/lkdtm/stackleak.c

@@ -74,8 +74,8 @@ void lkdtm_STACKLEAK_ERASING(void)
 
 end:
 	if (test_failed) {
-		pr_err("FAIL: the thread stack is NOT properly erased\n");
+		pr_err("FAIL: the thread stack is NOT properly erased!\n");
-		dump_stack();
+		pr_expected_config(CONFIG_GCC_PLUGIN_STACKLEAK);
 	} else {
 		pr_info("OK: the rest of the thread stack is properly erased\n");
 	}

drivers/misc/lkdtm/usercopy.c

@@ -173,6 +173,8 @@ static void do_usercopy_heap_size(bool to_user)
 			goto free_user;
 		}
 	}
+	pr_err("FAIL: bad usercopy not detected!\n");
+	pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
 
 free_user:
 	vm_munmap(user_addr, PAGE_SIZE);
@@ -248,6 +250,8 @@ static void do_usercopy_heap_whitelist(bool to_user)
 			goto free_user;
 		}
 	}
+	pr_err("FAIL: bad usercopy not detected!\n");
+	pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
 
 free_user:
 	vm_munmap(user_alloc, PAGE_SIZE);
@@ -319,7 +323,8 @@ void lkdtm_USERCOPY_KERNEL(void)
 		pr_warn("copy_to_user failed, but lacked Oops\n");
 		goto free_user;
 	}
-	pr_err("FAIL: survived bad copy_to_user()\n");
+	pr_err("FAIL: bad copy_to_user() not detected!\n");
+	pr_expected_config_param(CONFIG_HARDENED_USERCOPY, "hardened_usercopy");
 
 free_user:
 	vm_munmap(user_addr, PAGE_SIZE);

tools/testing/selftests/lkdtm/stack-entropy.sh

@@ -30,6 +30,7 @@ rm -f "$log"
 
 # We would expect any functional stack randomization to be at least 5 bits.
 if [ "$bits" -lt 5 ]; then
+	echo "Stack entropy is low! Booted without 'randomize_kstack_offset=y'?"
 	exit 1
 else
 	exit 0