[PATCH 1/2] kunit: test: Add vm_mmap() allocation resource manager

[Kees Cook]

For tests that need to allocate using vm_mmap() (e.g. usercopy and
execve), provide the interface to have the allocation tracked by KUnit
itself. This requires bringing up a placeholder userspace mm.

This combines my earlier attempt at this with Mark Rutland's version[1].

Link: https://lore.kernel.org/lkml/20230321122514.1743889-2-mark.rutland@xxxxxxx/ [1]
Co-developed-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 include/kunit/test.h |  17 ++++++
 lib/kunit/test.c     | 139 ++++++++++++++++++++++++++++++++++++++++++-
 2 files changed, 155 insertions(+), 1 deletion(-)

diff --git a/include/kunit/test.h b/include/kunit/test.h
index 61637ef32302..8c3835a6f282 100644
--- a/include/kunit/test.h
+++ b/include/kunit/test.h
@@ -478,6 +478,23 @@ static inline void *kunit_kcalloc(struct kunit *test, size_t n, size_t size, gfp
 	return kunit_kmalloc_array(test, n, size, gfp | __GFP_ZERO);
 }
 
+/**
+ * kunit_vm_mmap() - Allocate KUnit-tracked vm_mmap() area
+ * @test: The test context object.
+ * @file: struct file pointer to map from, if any
+ * @addr: desired address, if any
+ * @len: how many bytes to allocate
+ * @prot: mmap PROT_* bits
+ * @flag: mmap flags
+ * @offset: offset into @file to start mapping from.
+ *
+ * See vm_mmap() for more information.
+ */
+unsigned long kunit_vm_mmap(struct kunit *test, struct file *file,
+			    unsigned long addr, unsigned long len,
+			    unsigned long prot, unsigned long flag,
+			    unsigned long offset);
+
 void kunit_cleanup(struct kunit *test);
 
 void __printf(2, 3) kunit_log_append(struct string_stream *log, const char *fmt, ...);
diff --git a/lib/kunit/test.c b/lib/kunit/test.c
index 1d1475578515..09194dbffb63 100644
--- a/lib/kunit/test.c
+++ b/lib/kunit/test.c
@@ -11,13 +11,14 @@
 #include <kunit/test-bug.h>
 #include <kunit/attributes.h>
 #include <linux/kernel.h>
+#include <linux/kthread.h>
+#include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
 #include <linux/mutex.h>
 #include <linux/panic.h>
 #include <linux/sched/debug.h>
 #include <linux/sched.h>
-#include <linux/mm.h>
 
 #include "debugfs.h"
 #include "device-impl.h"
@@ -871,6 +872,142 @@ void kunit_kfree(struct kunit *test, const void *ptr)
 }
 EXPORT_SYMBOL_GPL(kunit_kfree);
 
+struct kunit_vm_mmap_resource {
+	unsigned long addr;
+	size_t size;
+};
+
+/* vm_mmap() arguments */
+struct kunit_vm_mmap_params {
+	struct file *file;
+	unsigned long addr;
+	unsigned long len;
+	unsigned long prot;
+	unsigned long flag;
+	unsigned long offset;
+};
+
+/*
+ * Arbitrarily chosen user address for the base allocation.
+ */
+#define UBUF_ADDR_BASE	SZ_2M
+
+/* Create and attach a new mm if it doesn't already exist. */
+static int kunit_attach_mm(void)
+{
+	struct vm_area_struct *vma;
+	struct mm_struct *mm;
+
+	if (current->mm)
+		return 0;
+
+	mm = mm_alloc();
+	if (!mm)
+		return -ENOMEM;
+
+	if (mmap_write_lock_killable(mm))
+		goto out_free;
+
+	/* Define the task size. */
+	mm->task_size = TASK_SIZE;
+
+	/* Prepare the base VMA. */
+	vma = vm_area_alloc(mm);
+	if (!vma)
+		goto out_unlock;
+
+	vma_set_anonymous(vma);
+	vma->vm_start = UBUF_ADDR_BASE;
+	vma->vm_end = UBUF_ADDR_BASE + PAGE_SIZE;
+	vm_flags_init(vma, VM_READ | VM_MAYREAD | VM_WRITE | VM_MAYWRITE);
+	vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
+
+	if (insert_vm_struct(mm, vma))
+		goto out_free_vma;
+
+	mmap_write_unlock(mm);
+
+	/* Make sure we can allocate new VMAs. */
+	arch_pick_mmap_layout(mm, &current->signal->rlim[RLIMIT_STACK]);
+
+	/* Attach the mm. It will be cleaned up when the process dies. */
+	kthread_use_mm(mm);
+
+	return 0;
+
+out_free_vma:
+	vm_area_free(vma);
+out_unlock:
+	mmap_write_unlock(mm);
+out_free:
+	mmput(mm);
+	return -ENOMEM;
+}
+
+static int kunit_vm_mmap_init(struct kunit_resource *res, void *context)
+{
+	struct kunit_vm_mmap_params *p = context;
+	struct kunit_vm_mmap_resource vres;
+	int ret;
+
+	ret = kunit_attach_mm();
+	if (ret)
+		return ret;
+
+	vres.size = p->len;
+	vres.addr = vm_mmap(p->file, p->addr, p->len, p->prot, p->flag, p->offset);
+	if (!vres.addr)
+		return -ENOMEM;
+	res->data = kmemdup(&vres, sizeof(vres), GFP_KERNEL);
+	if (!res->data) {
+		vm_munmap(vres.addr, vres.size);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+static void kunit_vm_mmap_free(struct kunit_resource *res)
+{
+	struct kunit_vm_mmap_resource *vres = res->data;
+
+	/*
+	 * Since this is executed from the test monitoring process,
+	 * the test's mm has already been torn down. We don't need
+	 * to run vm_munmap(vres->addr, vres->size), only clean up
+	 * the vres.
+	 */
+
+	kfree(vres);
+	res->data = NULL;
+}
+
+unsigned long kunit_vm_mmap(struct kunit *test, struct file *file,
+			    unsigned long addr, unsigned long len,
+			    unsigned long prot, unsigned long flag,
+			    unsigned long offset)
+{
+	struct kunit_vm_mmap_params params = {
+		.file = file,
+		.addr = addr,
+		.len = len,
+		.prot = prot,
+		.flag = flag,
+		.offset = offset,
+	};
+	struct kunit_vm_mmap_resource *vres;
+
+	vres = kunit_alloc_resource(test,
+				    kunit_vm_mmap_init,
+				    kunit_vm_mmap_free,
+				    GFP_KERNEL,
+				    &params);
+	if (vres)
+		return vres->addr;
+	return 0;
+}
+EXPORT_SYMBOL_GPL(kunit_vm_mmap);
+
 void kunit_cleanup(struct kunit *test)
 {
 	struct kunit_resource *res;
-- 
2.34.1