[PATCH v2] kunit/usercopy: Disable testing on !CONFIG_MMU

[Kees Cook <kees@kernel.org>]

Since arch_pick_mmap_layout() is an inline for non-MMU systems, disable
this test there.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202406160505.uBge6TMY-lkp@intel.com/
Signed-off-by: Kees Cook <kees@kernel.org>
---
Resending as v2 with Shuah in To:
---
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Brendan Higgins <brendan.higgins@linux.dev>
Cc: David Gow <davidgow@google.com>
Cc: Rae Moar <rmoar@google.com>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kselftest@vger.kernel.org
Cc: kunit-dev@googlegroups.com
Cc: linux-hardening@vger.kernel.org
Cc: linux-mm@kvack.org
---
 lib/kunit/user_alloc.c | 4 ++++
 lib/usercopy_kunit.c   | 5 +++++
 mm/util.c              | 2 ++
 3 files changed, 11 insertions(+)

diff --git a/lib/kunit/user_alloc.c b/lib/kunit/user_alloc.c
index 76d3d1345ed7..ae935df09a5e 100644
--- a/lib/kunit/user_alloc.c
+++ b/lib/kunit/user_alloc.c
@@ -30,6 +30,10 @@ static int kunit_attach_mm(void)
 	if (current->mm)
 		return 0;
 
+	/* arch_pick_mmap_layout() is only sane with MMU systems. */
+	if (!IS_ENABLED(CONFIG_MMU))
+		return -EINVAL;
+
 	mm = mm_alloc();
 	if (!mm)
 		return -ENOMEM;
diff --git a/lib/usercopy_kunit.c b/lib/usercopy_kunit.c
index 45f1e558c464..e819561a540d 100644
--- a/lib/usercopy_kunit.c
+++ b/lib/usercopy_kunit.c
@@ -290,6 +290,11 @@ static int usercopy_test_init(struct kunit *test)
 	struct usercopy_test_priv *priv;
 	unsigned long user_addr;
 
+	if (!IS_ENABLED(CONFIG_MMU)) {
+		kunit_skip(test, "Userspace allocation testing not available on non-MMU systems");
+		return 0;
+	}
+
 	priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL);
 	KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv);
 	test->priv = priv;
diff --git a/mm/util.c b/mm/util.c
index df37c47d9374..e70e8e439258 100644
--- a/mm/util.c
+++ b/mm/util.c
@@ -484,7 +484,9 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 	clear_bit(MMF_TOPDOWN, &mm->flags);
 }
 #endif
+#ifdef CONFIG_MMU
 EXPORT_SYMBOL_IF_KUNIT(arch_pick_mmap_layout);
+#endif
 
 /**
  * __account_locked_vm - account locked pages to an mm's locked_vm
-- 
2.34.1