kunit: test: Add vm_mmap() allocation resource manager

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].

Normally alloc_mm() and arch_pick_mmap_layout() aren't exported for
modules, so export these only for KUnit testing.

Link: https://lore.kernel.org/lkml/20230321122514.1743889-2-mark.rutland@arm.com/ [1]
Co-developed-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Kees Cook <kees@kernel.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

include/kunit/test.h

@@ -480,6 +480,23 @@ 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, ...);

kernel/fork.c

@@ -115,6 +115,8 @@
 #define CREATE_TRACE_POINTS
 #include <trace/events/task.h>
 
+#include <kunit/visibility.h>
+
 /*
  * Minimum number of threads to boot the kernel
  */
@@ -1334,6 +1336,7 @@ struct mm_struct *mm_alloc(void)
 	memset(mm, 0, sizeof(*mm));
 	return mm_init(mm, current, current_user_ns());
 }
+EXPORT_SYMBOL_IF_KUNIT(mm_alloc);
 
 static inline void __mmput(struct mm_struct *mm)
 {

lib/kunit/Makefile

@@ -2,6 +2,7 @@ obj-$(CONFIG_KUNIT) +=			kunit.o
 
 kunit-objs +=				test.o \
 					resource.o \
+					user_alloc.o \
 					static_stub.o \
 					string-stream.o \
 					assert.o \

lib/kunit/user_alloc.c

@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * KUnit userspace memory allocation resource management.
+ */
+#include <kunit/resource.h>
+#include <kunit/test.h>
+#include <linux/kthread.h>
+#include <linux/mm.h>
+
+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;
+};
+
+/* Create and attach a new mm if it doesn't already exist. */
+static int kunit_attach_mm(void)
+{
+	struct mm_struct *mm;
+
+	if (current->mm)
+		return 0;
+
+	mm = mm_alloc();
+	if (!mm)
+		return -ENOMEM;
+
+	/* Define the task size. */
+	mm->task_size = TASK_SIZE;
+
+	/* 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;
+}
+
+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);
+
+MODULE_IMPORT_NS(EXPORTED_FOR_KUNIT_TESTING);

mm/util.c

@@ -26,6 +26,8 @@
 
 #include <linux/uaccess.h>
 
+#include <kunit/visibility.h>
+
 #include "internal.h"
 #include "swap.h"
 
@@ -482,6 +484,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
 	clear_bit(MMF_TOPDOWN, &mm->flags);
 }
 #endif
+EXPORT_SYMBOL_IF_KUNIT(arch_pick_mmap_layout);
 
 /**
  * __account_locked_vm - account locked pages to an mm's locked_vm